CB Flashcards

Question

A patient presents with diarrhea and abdominal cramping. The organism isolated from the stool culture is identified as Shigella dysenteriae (group A). The TSI reaction would have indicated:* a. K/K b. K/NC H2S+ c. A/A d. K/A

Answer 1

A The traditional gravity displacement of steam sterilization cycle is 121˚C for 15 minutes at 15 pounds per square inch. Ethylene dioxide is an alternative sterilization method.

Answer 2

C Human blood contains substance that may inhibit microbial growth. Diluting blood in culture broth reduces the concentration of theses substances as well ass any antibiotics that may be present. The recommended bloodbroth ratio is 1:5 to 1:10. Dilutions less than this may cause blood to clot, trapping microorganisms in the clot. Greater dilutions may increase the time of detection.

Answer 3

C Most commercially available blood culture media contain sodium polyanethol sulfonate (SPS) in concentration between 0.025 and 0.050%. SPS has anticoagulant activity and inactivates neutrophils as well as some antibiotics including gentamicin and polymyxin. It also precipitates components of serum complement.

Answer 4

D Indwelling catheters are closed systems and should not be disconnected for specimen collection. Urine samples should not be collected from catheter bags, and Foley catheter tips are unsuitable for culture because they are contaminated with colonizing organisms. Urine from indwelling catheters should be collected by aseptically puncturing the tubing (collection port).

Answer 5

D Urine is an appropriate specimen for the detection of renal tuberculosis. Since feces contain anaerobic organisms as part of the indigenous flora, it is an unacceptable specimen for anaerobic culture. Foley catheter tips are also not acceptable for culture because they are contaminated with colonizing organisms. Gram stain smears of rectal swabs for N. gonorrhoeae should also not be performed, since the presence of organisms with similar morphologies may lead to over interpretation of smears.

Answer 6

C Materials collected from sites not harboring indigenous normal flora (sterile body fluids, abscesses, exudates and tissue) should be culture for anaerobic bacteria, however, since anaerobes normally inhabit the skin and mucus membrane as part of indigenous normal flora, specimens such as urine, sputum and vaginal, eye and ear swabs are not acceptable for culture.

Answer 7

C The use of swabs for collection of specimens for anaerobic culture is discouraged. Aspiration with a needle and syringe is recommended. Whenever possible cultures should be obtained before the administration of antibiotics to optimize organism recovery

Answer 8

C Enriched media such as chocolate agar has no inhibitory effects on bacterial growth and contains additional nutrients that support the growth of fastidious organisms such as H. influenzae and Neisseria.

Answer 9

C Urine, stool, viral specimens, sputa, swabs, and foreign devices such as catheters should be stored at 4°C. Serum for serologic studies may be frozen for up to 1 week at –20°C, and tissues or specimens for long-term storage should be frozen at –70°C.

Answer 10

C Variations in the concentrations of divalent cations, primarily calcium and magnesium affect the results of aminoglycoside, tetracycline and colistin test with Pseudomonas aeruginosa isolates. A cation concentration that is too high results in smaller zone sized and a concentration that is too low increase zone sizes.

Answer 11

C All Mueller Hinton Agar used for disk diffusion susceptibility testing should be poured to a depth of 4mm. If the depth of the media is <4mm, this may be associated with excessively large zones and false positive susceptibility results. Agar that is >4mm in depth may cause excessively small zone sizes.

Answer 12

B * Daily disk diffusion quality control can be converted to weekly testing when 30 days of consecutive testing demonstrated no more than 3 antibiotic/ organism combinations outside the acceptable limits.

Answer 13

B * The amount of antibiotic used in disk diffusion susceptibility testing is standardized and constant. Once the disk is placed on the inoculated plate and makes contact with the agar, the antibiotic in the disk begins to diffuse out. As it diffuses into the media, the concentration of antibiotic gets lower the further it diffuses from the disk.

Answer 14

C A delay of more than 15 minutes between placing the disks on an inoculated plate and incubation permits excess prediffusion of the antimicrobial agent from the disk. This would result in a larger than expected zone diameter.

Answer 15

B To ensure the reproducibility of disk diffusion testing, the inoculum must be standardized. If the inoculum is too dense (too many organisms) zone sizes would be smaller than expected and appear falsely resistant.

Answer 16

A A thin film of growth appearing in the zone area of inhibition around the susceptibility disk should be ignored when swarming Proteus or other organisms are encountered. Discontinuous, poor growth or tiny colonies near the end of the zone should also be ignored.

Answer 17

B Penicillin inhibits penicillin-binding proteins that are essential to peptidoglycan (cell wall) synthesis. Chloramphenicol inhibits protein synthesis, colistin increases cell membrane permeability and sulfamethoxazole inhibits folate metabolism.

Answer 18

A * The gram stain and culture growth describe a Staphylococcus species. Catalase production confirms that the organism belong to the genus Staphylococcus and coagulase is used to differentiate S. aureus from coagulase negative staphylococci

Answer 19

A Slide coagulase - cell-bound coagulase or clumping factor * Tube coagulase - free coagulase

Answer 20

B The organism in this urine culture is a Staphylococcus species. Coagulase will differentiate S. aureus from coagulase negative staphylococci (CoNS) and novobiocin susceptibility will differentiate S. saprophyticus from other CoNS. S. saprophyticus is a common cause of urinary tract infections in young females

Answer 21

A S. intermedius infects mammals and certain birds but not usually humans. Cases involving humans result from animal bites and are most often seen in persons who work closely with animals.

Answer 22

A The production of acetoin by S. aureus from glucose or pyruvate differentiates it from S. intermedius, which is also coagulase positive. * This test is also called the VP test. Acetoin production is detected by addition of 40% KOH and 1% α-naphthol to the VP test broth after 48 hours of incubation. A distinct pink color within 10 minutes denotes a positive test.

Answer 23

B S. epidermidis produces an extracellular slime that enhances the adhesion of these organisms to indwelling plastic catheters. The slime production is considered a virulence factor and is associated with infections from prostheses.

Answer 24

B Coagulase-negative staphylococci are commonly associated with contaminated blood cultures; however, they are also increasing as a cause of true bacteremia. Significant bacteremia in a patient with endocarditis is usually continuous and low grade. In most cases, all blood cultures drawn will yield positive results. The facts that only 1 bottle of 1 set was positive, and that the bottle did not become positive until day 5 of incubation indicate that this isolate is most likely a contaminant.

Answer 25

B By using a 15-μg erythromycin disk adjacent to a 2-μg clindamycin disk in a disk diffusion procedure, a flattening of the clindamycin zone occurs in inducible clindamycin resistance, causing the zone to look like the letter D. This is referred to as being D-zone positive. CLSI recommends that inducible clindamycin resistant strains be reported as resistant with a comment that clindamycin may still be effective in some patients

Answer 26

B Streptococcus pyogenes, Not considered normal flora * Inhabits skin and upper respiratory tract of humans, carried on nasal, pharyngeal, and, sometimes, anal mucosa; presence in specimens is almost always considered clinically significant

Answer 27

A Bile esculin, PYR, bacitracin and hippurate are biochemical test for the presumptive or definitive identification of beta hemolytic streptococci. Such as S. pyogenes, S. aggalactiae and Enterococcus.

Answer 28

B Detection of group B streptococcus (GBS) in the genital and gastrointestinal tracts of pregnant women can identify infants at risk for GBS infection. The CDC recommends the collection of vaginal and rectal swab or a single swab inserted first into the vagina and then the rectum at 35 to 37 weeks of gestation. The swab(s) should be inoculated into a selective broth medium such as LIM broth (ToddHewitt broth with colistin and nalidixic acid). The use of vaginal/rectal swabs and selective broth medium greatly increases the recovery of GBS.

Answer 29

D Bile solubility testing of alpha hemolytic streptococci differentiates S. pneumoniae (soluble) from other alphahemolytic streptococci such as viridans streptococci (insoluble)

Answer 30

C Optochin susceptibility is used to differentiate S. pneumoniae, which are susceptible from other alpha hemolytic streptococci which are resistant.

Answer 31

B Non-infectious sequelae associated with infection with Streptococcus pyogenes are glomerulonephritis and rheumatic fever

Answer 32

B Streptolysin O - subsurface hemolysis * Streptolysin S - surface hemolysis

Answer 33

B The bile solubility test can be performed directly by dropping 2% sodium deoxycholate onto a few well-isolated colonies of S. pneumoniae. The bile salts speed up the autolysis observed in pneumococcal cultures. The colonies lyse and disappear when incubated at 35°C for 30 min, leaving a partially hemolyzed area on the plate.

Answer 34

B Approximately 80% of group B streptococci are capable of growing in 6.5% salt broth; however, they do not hydrolyze esculin or grow in media containing 4% bile salts.

Answer 35

A The PYR hydrolysis test is highly specific for group A streptococci and group D enterococci. The test detects the pyrrolidonylarylamidase enzyme, which hydrolyzes PYR.

Answer 36

D MTM, New York City, and Martin–Lewis agars contain blood factors needed to support the growth of N. gonorrhoeae as well as antibiotics that prevent growth of normal genital flora. Cultures must be incubated in 3%– 7% CO2 at 35°C. Cultures should be held a minimum of 48 hours before being considered negative.

Answer 37

A Specimens for culture of N. gonorrhoeae are best if plated immediately or transported in a medium containing activated charcoal to absorb inhibitory substances that hinder their recovery

Answer 38

B Antimicrobial resistance in Neisseria gonorrhea is widespread. The production of beta-lactamase (penicillinase) breaks open the beta lactam ring of penicillin, destroying its activity. Thus, N. gonorrhoeae that produces beta lactamase are resistant to penicillin.

Answer 39

B Neisseria gonorrhoeae is oxidase positive and ferments glucose but not maltose

Answer 40

C XLD agar is selective for gram-negative coliforms because of a high concentration (0.25%) of deoxycholate, which inhibits gram-positive bacteria. * In addition, XLD is differential for Shigella and Salmonella spp. The medium contains xylose, lactose, and sucrose, which are fermented by most normal intestinal coliforms producing yellow colonies. * Shigella does not ferment the sugars and produces red (or clear) colonies. Salmonella spp. ferment xylose; however, they also decarboxylate lysine in the medium, causing production of ammonia. Therefore, Salmonella first appear yellow but become red. Some Salmonella produce hydrogen sulfide (H2S) from sodium thiosulfate and therefore appear as red colonies with black centers.

Answer 41

C E. coli 0157:H7 ferments lactose, and therefore, appears as dark pink colonies on MacConkey agar. To differentiate E. coli 0157:H7 from normal fecal flora, MacConkey agar with sorbitol is used. E. coli 0157:H7 does not ferment sorbitol, and usually are colorless colonies.

Answer 42

A All Enterobacteriaceae ferment glucose and are oxidase negative and nonsporulating. Most Enterobacteriaceae are motile, but the genera Shigella and Klebsiella are not.

Answer 43

A Acetoin or acetylcarbinol, an end product of glucose fermentation, is converted to diacetyl after the addition of the VP reagents (α-naphthol and 40% potassium hydroxide [KOH]). Diacetyl is seen as a red- to pinkcolored complex

Answer 44

D Both MR and VP tests detect acid production from the fermentation of glucose. However, a positive MR test denotes a more complete catabolism of glucose to highly acidic end products such as formate and acetate than occurs with organisms that are VP positive only (e.g., Klebsiella pneumoniae).

Answer 45

A The Simmons citrate test determines if an organism can utilize citrate as the sole source of carbon. The medium turns blue, indicating the presence of alkaline products such as carbonate. Tubes are incubated a minimum of 24 hours at 35°C with a loose cap before reading.

Answer 46

A The indole test detects the conversion of tryptophan (present in the media) to indole by the enzyme tryptophanase. Indole is detected by the reaction with the aldehyde group of p-dimethylaminobenzaldehyde (the active reagent in Kovac’s and Ehrlich’s reagents) in acid, forming a red complex.

Answer 47

C Putrescine is the amine product of the decarboxylation of ornithine.

Answer 48

B Phenylalanine deaminase oxidatively deaminates phenylalanine, forming phenylpyruvic acid. When a solution of ferric chloride is added, the iron reacts with phenylpyruvic acid, forming a green-colored complex. Phenylalanine deaminase is found in the genera Morganella, Providencia, and Proteus and is an excellent test to determine if an organism belongs to this group. Rarely, isolates of Enterobacter may be phenylalanine deaminase positive as well.

Answer 49

B Escherichia, Salmonella, Shigella, and Yersinia are responsible for the majority of enteric diarrhea cases attributable to the Enterobacteriaceae family.

Answer 50

A Shigella spp. and Klebsiella spp. are for the most part nonmotile. Yersinia can be motile at 22°C but is nonmotile at 36°C

Answer 51

A Shigella spp. and Campylobacter spp. are both causes of diarrhea, abdominal pain, fever, and sometimes vomiting. Blood is present in the stools of patients infected with Shigella as a result of invasion and penetration of the bowel. Young children may also exhibit bloody stools when infected with Campylobacter.

Answer 52

B Campylobacter continues to be the most common enteric pathogen isolated from patients with diarrhea. Routinely fecal specimens should be cultured for Salmonella, Shigella and Campylobacter. Fecal specimens are not routinely cultured for enterotoxaemia E. coli or C. outline. E. Hartman is a non-pathogenic parasite and does not cause diarrhea.

Answer 53

D Cold enrichment is especially useful when specimens contain large numbers of normal flora that are sensitive to prolonged exposure to near-freezing temperature. In addition to Yersinia, the technique has been used to enhance recovery of Listeria monocytogenes from specimens containing other bacteria.

Answer 54

B More than 80% of uncomplicated UTIs are caused by Escherichia coli.

Answer 55

D Shigella is lactose negative, most species do not produce gas, are VP, urea, lysine decarboxylase and citrate negative, and they are non motile.

Answer 56

B E. coli can produce several different types of toxins that result in different gastroenteritis and manifestations.

Answer 57

D Yersinia pestis is classically described as having a “safety pin” appearance on Wayson’s stain. This patient’s presentation is classic for bubonic plague.

Answer 58

A E. sakazakii is called a yellow-pigmented E. cloacae and is best differentiated from E. cloacae by sorbitol fermentation (95% positive for E. cloacae and 0% for E. sakazakii). In addition, E. cloacae is usually positive for urease and malonate (65% and 75%, respectively) and E. sakazakii is usually negative (1% and < 20%, respectively). Both species are usually motile and arginine dihydrolase positive.

Answer 59

D K. oxytoca and K. pneumoniae are almost identical biochemically except for the ability to produce indole. Both organisms are usually positive for urease, sucrose, and citrate. However, K. oxytoca is indole positive and K. pneumoniae is indole negative.

Answer 60

B Strains of E. coli that produce one or both of the Shiga-like toxins (SLT I and SLT II) can cause bloody diarrhea (hemorrhagic colitis). In the United States, E. coli strain O157:H7 is the serotype most often associated with hemorrhagic colitis.

Answer 61

B S. marcescens has been implicated in numerous nosocomial infections and is recognized as an important pathogen with invasive properties. Gelatin hydrolysis and DNase are positive for both the Proteus spp. and Serratia, but the negative urease and phenylalanine deaminase are differential.

Answer 62

A Although P. mirabilis is more frequently recovered from patients with urinary tract infections, P. vulgaris is commonly recovered from immunosuppressed patients. P. mirabilis is indole negative and ornithine decarboxylase positive but otherwise is very similar to P. vulgaris.

Answer 63

A Enterobacteriaceae ferments glucose and are oxidase negative. Pleisomonas was a member of the Vibrio family in part because it is oxidase positive. However it was moved to the Enterobacteriaceae despite its positive oxidase reaction.

Answer 64

D Pseudomonas aeruginosa: Positive for mannitol, nitrate reduction and growth at 42C Pseudomonas putida: Negative for mannitol, nitrate reduction and growth at 42C

Answer 65

B P. aeruginosa is often recovered from the respiratory secretions of cystic fibrosis patients. If the patient is chronically infected with the mucoid strain of P. aeruginosa, the biochemical identification is very difficult. The mucoid strain results from production of large amounts of alginate, a polysaccharide that surrounds the cell

Answer 66

D P. aeruginosa is highly resistant to many antimicrobial drugs as well as being one of the most often cultured opportunistic organisms. This virulence factor allows for many nosocomial infections such as those of the urinary tract, wounds (burn patients), bacteremia, respiratory tract, and CNS.

Answer 67

D B. pseudomallei produces wrinkled colonies resembling P. stutzeri. Infections are usually asymptomatic and can be diagnosed only by serological methods. The organism exists in soil and water in an area of latitude 20° north and south of the equator (mainly in Thailand and Vietnam). Thousands of U.S. military personnel were infected with these bacteria during the 1960s and 1970s. The disease may reactivate many years after exposure and has been called the “Vietnamese time bomb.”

Answer 68

B Cetrimide (acetyl trimethyl ammonium bromide) agar is used for the isolation and identification of P. aeruginosa. With the exception of P. fluorescens, the other pseudomonads are inhibited along with related nonfermentative bacteria.

Answer 69

D Thiosulfate citrate bile salts agar is a selective media for Vibrio and it also differentiates sucrose fermenting species such as V. cholerae and V. alginolyticus.

Answer 70

A Campylobacter are gram negative, curved bacilli that require microaerophilic conditions for growth.

Answer 71

A Helicobacter pylori produce large amounts of extracellular urease and are positive for urea within 2 hours.

Answer 72

D * H. pylori: positive for urease; negative for nitrate reduction and hippurate hydrolysis * C. jejuni: negative for urease; positive for nitrate reduction and hippurate hydrolysis

Answer 73

B Pasteurella multocida (P. canis) is part of the normal mouth flora of cats and dogs and is frequently recovered from wounds inflicted by them. It produces large amounts of indole and therefore an odor resembling colonies of E. coli. Pseudomonas spp. are also catalase and oxidase positive but can be ruled out because they grow on MacConkey agar and do not produce indole.

Answer 74

C F. tularensis is a fastidious gram-negative rod that is best recovered from lymph node aspirates and tissue biopsies. It is oxidase negative, nonmotile, and inert biochemically. Cysteine blood agar is the medium of choice, but F. tularensis will grow on commercially prepared chocolate agar because it contains X factor and is supplemented with a growth enrichment (IsoVitaleX) that contains cysteine. F. tularensis may not grow well on MacConkey agar

Answer 75

B Production of β-hemolysis is used to distinguish these two species from other Haemophilus with the same X and V requirements. Horse blood agar furnishes X factor and, when supplemented with yeast extract, supports the growth of Haemophilus spp. Sheep blood agar is not used because it contains growth inhibitors for some Haemophilus spp.

Answer 76

B H. ducreyi requires exogenous X factor and causes genital lesions referred to as “soft chancres.”

Answer 77

A L. pneumophila is the cause of pneumonia and can occur as part of an epidemic sporadically or nosocomially, or may be community acquired. The appearance of mottled, cut-glass colonies on buffered CYE agar under low power and the use of a direct immunofluorescence technique on sputum samples determine the presence of L. pneumophila. * The most common environmental sites for recovery are shower heads, faucets, water tanks, and air-conditioning systems

Answer 78

B The only spore former listed is the Bacillus spp., which grow as large, spreading colonies on blood agar plates. Pseudomonas spp. are gram-negative rods; Corynebacterium spp. appear as small, very dry colonies on BAP; Listeria spp. appear as very small β-hemolytic colonies on BAP, resembling Streptococcus species.

Answer 79

A Both species of Bacillus are catalase and lecithinase positive and produce acid from glucose. B. cereus is βhemolytic and motile, but B. anthracis is neither.

Answer 80

A The best differentiating test to perform on a suspected B. anthracis culture is the 10-unit penicillin disk test. B. anthracis is susceptible but other Bacillus spp. are not

Answer 81

D The best specimen is the suspected food itself. Stool cultures are not useful because B. cereus is part of the normal fecal flora. The suspected food can be the source of food poisoning by B. cereus if 100,000 or greater organisms per gram of infected food are demonstrated.

Answer 82

D Wounds infected with clostridia are characterized by invasion and liquefactive necrosis of muscle tissue with gas formation. The most frequent isolate is C. perfringens followed by C. novyi and C. septicum.

Answer 83

C C. perfringens produces a double zone of β-hemolysis on blood agar, which makes identification relatively easy. The inner zone of complete hemolysis is caused by a θ-toxin and the outer zone of incomplete hemolysis is caused by an α-toxin (lecithinase activity). * The Bacteroides spp. are gram-negative bacilli, and C. difficile is lecithinase negative and does not produce a double zone of β-hemolysis.

Answer 84

A Egg yolk agar (modified McClung’s or neomycin egg yolk agar) is used to determine the presence of lecithinase activity, which causes an insoluble, opaque, whitish precipitate within the agar. * Lipase activity is indicated by an iridescent sheen or pearly layer on the surface of the agar

Answer 85

D LIPASE + C. botulinum, C. sporogenes and C. novyi. * Lipase is produced by some Clostridium spp. and is seen as an iridescent pearly layer on the surface of the colonies that extends onto the surface of the egg yolk agar medium surrounding them. C. perfringens, the most frequently isolated Clostridium species, is negative for lipase production.

Answer 86

B Foodborne botulism in adults and children is caused by ingestion of the preformed toxin (botulinum toxins A, B, E, and F) in food. * The neurotoxins of C. botulinum are protoplastic proteins made during the growing phase and released during lysis of the organisms. Confirmation of botulism is made by demonstration of the toxin in serum, gastric, or stool specimens

Answer 87

A Epidemiological studies have demonstrated that infant botulism results from the ingestion of spores via breastfeeding or exposure to honey. Preformed toxin has not been detected in food or liquids taken by the infants. C. botulinum multiplies in the gut of the infant and produces the neurotoxin in situ.

Answer 88

A Definitive identification of C. botulinum is made by the toxin neutralization test for its neurotoxins in serum or feces.

Answer 89

A Spore appearance and location, along with Gram stain morphology, aids in distinguishing the Clostridium spp. * Round, terminal spores are demonstrated when C. tetani is grown in chopped meat with glucose broth. Recognition of spores is particularly important because C. tetani sometimes appears as gram negative

Answer 90

D The culture and Gram stain of the puncture wound site usually does not produce any evidence of C. tetani. The diagnosis is usually based upon clinical findings, which are characterized by spastic muscle contractions, lockjaw, and backward arching of the back caused by muscle contraction.

Answer 91

B C. difficile is also implicated in hospital acquired diarrhea and colitis. Clinical testing for C. difficile includes culture and cytotoxin testing. Because culture takes 3 days and will detect nontoxigenic strains that do not cause diarrheal disease, immunoassays using antibodies against either the A toxin or both the A and B toxins are most frequently employed.

Answer 92

D CCFA is used for recovery of C. difficile from stool cultures. Cycloserine and cefoxitin inhibit growth of gram-negative coliforms in the stool specimen. C. difficile ferments fructose, forming acid that, in the presence of neutral red, causes the colonies to become yellow.

Answer 93

B Anaerobic bacteria can be identified by analysis of metabolic products using gas–liquid chromatography. Results are evaluated along with Gram staining characteristics, spore formation, and cellular morphology in order to make the identification

Answer 94

C C. diphtheriae must be recovered from the deep layers of the pseudomembrane that forms in the nasopharyngeal area. A flexible calcium alginate nasopharyngeal swab is the best choice for collecting a specimen from the posterior nares and pharynx.

Answer 95

A Corynebacterium spp. are part of the normal upper respiratory tract flora. Organisms display typical pleomorphic shapes often resembling letters such as Y or L, and metachromatic granules. Identification of C. diphtheriae, however, requires selective culture media and biochemical testing.

Answer 96

C Corynebacterium will grow on blood and chocolate agars, but Tinsdale agar is the preferred culture medium because the potassium tellurite in the agar causes C. diphtheriae to produce brown colonies surrounded by a brown halo. The halo effect is seen with C. diphtheriae, C. ulcerans, and C. pseudotuberculosis but not with other Corynebacterium or with other pigmented colonies growing on Tinsdale agar.

Answer 97

C In order to determine if an isolate of Corynebacterium diphtheriae produces toxin, testing for the presence of diphtheria toxin must be performed using methods such as Elek test or PCR.

Answer 98

A *Streptococci 1. Gram positive cocci in chains 2. Nonmotile 3. Catalase negative *Listeria 1. Gram positive bacilli 2. Motile 3. Catalase positive

Answer 99

C E. rhusiopathiae is catalase negative, whereas the other three organisms are catalase positive. E. rhusiopathiae is seen primarily as a skin infection on the fingers of meat and poultry workers. Colonies growing on blood agar are small and transparent, may be either smooth or rough, and are often surrounded by a green tinge. E. rhusiopathiae is characterized by H2S production in the butt of a TSI slant, which differentiates it from other catalase-negative, gram-positive rods.

Answer 100

A Lactobacillus spp. produce both long, slender rods or short coccobacilli that form chains. Lactobacillus spp. are part of the normal flora of the vagina (are not considered a pathogen) and are sometimes confused with the streptococci.

Answer 101

A A. israelii is part of the normal flora of the mouth and tonsils but may cause upper or lower respiratory tract infections. The sulfur granules are granular microcolonies with a purulent exudate.

Answer 102

B Nocardia spp. should be suspected if colonies that are partially acid fast by the traditional method are positive with the modified acid-fast method using Kinyoun stain and 1% sulfuric acid as the decolorizing agent. The other organisms listed are negative for acid-fast stain.

Answer 103

D All of the listed organisms produce mycelium (aerial or substrate), causing them to appear branched when Gram stained, but only the Nocardia spp. are positive for modified acid-fast stain. Nocardia is an opportunistic pathogen, and cultures typically have a musty basement odor

Answer 104

D Nocarida asteroides are partially acid fast and do not hydrolyze the substrates casein, tyrosine or xanthine.

Answer 105

A The carbolfuchsin (fuchsin with phenol) stains the mycobacteria red and does not decolorize after the acid– alcohol is added. The background and any other bacterial elements will decolorize and are counterstained blue by the methylene blue.

Answer 106

C All four media contain malachite green as an inhibitory agent of nonmycobacteria, but Petragnani’s medium contains a higher concentration (0.052 g/dL) than Löwenstein–Jensen (0.025 g/dL), Middlebrook 7H10 (0.0025 g/dL), or American Thoracic Society medium (0.02 g/dL). The last is used for normally sterile specimens, such as from CSF and bone marrow.

Answer 107

B Specimens submitted for culture and recovery of any bacteria should be submitted without fixatives.

Answer 108

B Niacin production is common to all mycobacteria. However, the niacin accumulates as a water-soluble metabolite in the culture medium when the organism cannot form niacin ribonucleotide. M. tuberculosis, M. simiae, and some strains of M. marinum, M. chelonae, and M. bovis lack the enzyme and therefore are called niacin positive because of the accumulation of niacin detected in the test medium.

Answer 109

A M. tuberculosis is positive for niacin accumulation, while the other three species are niacin negative. A serpentine pattern of growth indicates production of cording factor, a virulence factor for M. tuberculosis

Answer 110

D M. bovis is also called the bovine tubercle bacillus. A nonvirulent strain, bacillus Calmette–Guérin (BCG), is used as a tuberculosis vaccine throughout the world. Infections with M. bovis resemble infections caused by M. tuberculosis and are seen in circumstances where there is close contact between humans and cattle.

Answer 111

A M. bovis and M. tuberculosis are very similar biochemically, and some strains of M. bovis also accumulate niacin. The T2H test differentiates M. tuberculosis from M. bovis. * M. tuberculosis is not inhibited by T2H

Answer 112

C M. kansasii hydrolyses Tween 80 more rapidly than the other species (within 3–6 hours).

Answer 113

A More than 90% of MAC organisms that are isolated from AIDS patients are M. avium. These are distinguished from M. intraceulluare by NATs.

Answer 114

D M. gordonae is a nonpathogen, scotochromogen, and rapid grower (7 days at 37°C). Rarely, it is implicated in opportunistic infections in patients with shunts, prosthetic heart values, or hepatoperitoneal disease. The other three species are pathogenic mycobacteria

Answer 115

B M. paratuberculosis is known to cause an ulcerative intestinal disease with chronic diarrhea in cattle known as Johne’s disease. While M. paratuberculosis has been isolated from the intestines of humans with Crohn’s disease, the organism has not yet been proven to cause ileitis in humans.

Answer 116

A M. leprae and M. microti are different from all other mycobacteria because they cannot be cultured in vitro. * Biopsies from nodules and plaques of skin that show numerous AFB are presumptively diagnosed as positive for M. leprae. Confirmatory identification is made by nucleic acid testing (NAT) using PCR.

Answer 117

A Mycobacteria growing on MacConkey agar are usually nonpathogens. M. chelonae and M. fortuitum are both nonpathogenic rapid growers that will grow on MacConkey agar (with no crystal violet) within 5 days.

Answer 118

A Borrelia spp. are often seen on Wright’s-stained smears of peripheral blood as helical bacteria with 3–10 loose coils. They are gram negative but stain well with Giemsa’s stain

Answer 119

D Lyme disease may result in acute arthritis and meningitis and is caused by B. burgdorfer

Answer 120

A Serological analysis using immunofluorescence or an enzyme immunoassay is the method of choice for diagnosis of Lyme disease.

Answer 121

B Serological tests of the patient’s serum for evidence of syphilis are routinely performed, but culturing is not because research animals must be used for inoculation of the suspected spirochete. T. pallidum does not stain by either the Gram or acid-fast technique

Answer 122

A Chlamydiae are strict intracellular organisms and must be cultured using living cells. Direct smears can also be made at the time of culture. Staining cells with iodine may reveal the characteristic reddish-brown inclusions sometimes seen in Chlamydia infections. Fluorescein-conjugated monoclonal antibodies may be used to identify the organisms in infected cells.

Answer 123

B PCR is both sensitive and specific and may be performed on urine.

Answer 124

B A common cause of respiratory tract illness, M. pneumoniae, generally causes a self-limited infection (3– 10 days) and usually does not require antibiotic therapy. M. pneumoniae can be cultured from the upper and lower respiratory tracts onto specially enriched (diphasic) media, but is most frequently diagnosed by the change in antibody titer from acute to convalescent serum using enzyme immunoassay or other serological methods.

Answer 125

A Genital mycoplasmas (M. hominis and Ureaplasma urealyticum) are grown on specific agars. M. hominis is grown on “M” agar containing arginine and phenol red. Colonies of mycoplasma are 50–300 μm in diameter and display a “fried-egg” appearance with red holes.

Answer 126

A Correct answer: EIA testing and direct antigen testing * Adults may fail to produce an IgM response especially in recurrent infections, so the best confirmatory approach is a combination of EIA and direct antigen testing.

Answer 127

B U. urealyticum is the only human mycoplasma that hydrolyzes urea. The manganous chloride–urea test utilizes manganous chloride (MnCl2) in the presence of urea. Urease produced by the organism hydrolyzes the urea to ammonia. This reacts with MnCl2 forming manganese oxide, which is insoluble and forms a dark brown precipitate around the colonies. The reaction is observed under a dissecting microscope and is a rapid test for the identification of U. urealyticum.

Answer 128

D Ehrlichia and Anaplasma spp. are intracellular bacteria and are the causative agents of human monocytotropic ehrlichiosis (HME) and human granulocytotropic anaplasmosis (HGA). The organisms infect humans, dogs, and cattle through the bite of an infected Ixodes tick which also transmits Borrelia spp., causing Lyme disease.

Answer 129

D. Phage typing Detection of a single strain of bacteria (+) Plaque formation/ lysis

Answer 130

1. looks like chancre; soft painful (H. ducreyi) 2. hard, painless (T. pallidum)

Answer 131

1. Capnocytophaga 2. Vibrio cholerae 3. Campylobacter 4. Helicobacter pylori

Answer 132

1. Rapid breath test 2. Gastric biopsy --> Rapid urease (+)

Answer 133

1. Bacillus anthracis 2. Corynebacterium diphtheriae C. diptheriae = ACTION STAR - GUN: gun metal black colony on CTBA - CIGARETTE: Arrangement - BABES: Babes Ernst granules (metachromatic granules) - BULL: Bull's neck appearance

Answer 134

1. Mycoplasma pneumoniae 2. Haemophilus ducreyi 3. Thiomargarita namibiensis 4. Bacillus anthacis 5. Borrelia burgdorferi (10um)

Answer 135

1. EIEC > or = 100,000 CFU/mL -- explosive stool 2. 100-200 CFU/mL -- dysentery (bloody diarrhea), scanty bloody stool

Answer 136

1. Clostridium tetani 2. Botulinum toxin

Answer 137

a. Neisseria A. Neisseria -- No exotoxin with endotoxin B. gm (+) no endotoxin C. D. gm (-) with exotoxin and endotoxin All gm (-) are endotoxins not produced but are already in the membrane (Neisseria, Escherichia, Salmonella)

Answer 138

P. aeruginosa > B. cepacia > S. maltophilia Oxidizers infect lungs

Answer 139

1. Gloves 2. 30% 3. 0.03% 4. Hand sanitizer

Answer 140

Transformation Transduction Conjugation

Answer 141

Unicellular, prokaryotic microorganisms Infectious agents Among clinically relevant organisms, bacteria are single- cell prokaryotic microorganisms. Fungi and parasites are single-cell or multicellular eukaryotic organisms, as are plants and all higher animals. Viruses are dependent on host cells for survival and therefore are not considered cellular organisms but rather infectious agents.

Answer 142

Gram-negative bacteria

Answer 143

Endotoxin Endotoxins * General toxin common to almost all gram-negative bacteria * Composed of lipopolysaccharide portion of cell envelope * Released when gram-negative bacterial cell is destroyed * Effects on host include: 1. Disruption of clotting, causing clots to form throughout the body (i.e., disseminated intravascular coagulation [DIC]) 2. Fever 3. Activation of complement and immune systems 4. Circulatory changes that lead to hypotension, shock, and death

Answer 144

Exotoxin Exotoxins * Most commonly associated with gram-positive bacteria * Produced and released by living bacteria; do not require bacterial death for release * Specific toxins target specific host cells; the type of toxin varies with the bacterial species. * Some kill host cells and help spread bacteria in tissues (e.g., enzymes that destroy key biochemical tissue components or specifically destroy host cell membranes). * Some destroy or interfere with specific intracellular activities (e.g., interruption of protein synthesis, interruption of internal cell signals, or interruption of neuromuscular system).

Answer 145

Endemic Epidemic Pandemic Endemic: A disease constantly present at some rate of occurrence in a particular location Epidemic: A larger than normal number of diseased or infected individuals in a particular location Pandemic: An epidemic that spans the world Outbreak: A larger than normal number of diseased or infected individuals that occurs over a relatively short period

Answer 146

Disease incidence Disease prevalence

Answer 147

Signs Symptoms

Answer 148

Lungs Normal flora can offer the host protection against infections by providing competition to pathogenic bacteria. The lungs are not typically colonized with bacterial flora. When diagnosing lower respiratory track infections, procedures such as bronchoscopy or percutaneous transtracheal aspirate are used to obtain a specimen that is not contaminated by upper respiratory tract flora.

Answer 149

Lactobacillus The flora of the female genital tract changes with age and the associated effects of pH and estrogen concentration in the mucosa. Lacto- bacillus spp. are the predominant flora during childbearing years. Earlier and later in life, staphylococci and corynebacteria predominate.

Answer 150

Infectious aerosols Infectious aerosols put laboratory profes- sionals at risk for acquiring many diseases. The handling of clinical specimens that require pipetting, centrifugation, or decanting may produce infectious aerosols. Bacteria frequently are present in greater numbers in aerosol droplets than in the liquid medium.

Answer 151

Incineration

Answer 152

Laboratory director and supervisor

Answer 153

Larger than 0.3 um

Answer 154

Class I Biologic Safety Cabinet Class II Biologic Safety Cabinet

Answer 155

Class IIB BSC Class IIA BSC Class III BSC

Answer 156

BSL-2 agents BSL-4 agents

Answer 157

Type ABC Combination type ABC extinguishers are found in most laboratories so that personnel need not worry about which extinguisher to reach for in case of a fire.

Answer 158

S. pyogenes (Group A Strep)

Answer 159

Urethral Swab Urine

Answer 160

B. I, II, III, IV Gastric aspirate - infants

Answer 161

d. BAP, CAP MAC - Selective Differential CNA - Selective for gm (+) cocci Thioglycollate broth - Enrichment

Answer 162

NOTE: Enrichment broth: Selenite F broth

Answer 163

b. Smart incubator

Answer 164

C. Closest to the disk

Answer 165

Molecular techniques

Answer 166

A. Centrifuge

Answer 167

Calcium alginate/ Dacron swab Plastic Dacron/ Rayon swab Flocked swab (with nylon) No inner core to trap the sample (up to 90% recovered)

Answer 168

1. SSA -- XLD 2. Campy Bap/ Skirrow 3. TCBS 4. CIN 5. Mac Sorbitol 6. Mac

Answer 169

Chlamydia trachomatis

Answer 170

CLAPS = Gonorrhea CRABS = Ectoparasite Pubic crab - Pthirus pubis Pubic lice - Pediculus humanus (Human body louse) Head lice - Pediculus humanus var capitis Pubic lice is a vector of 3 bioterrorism agents: 1. Epidemic typhus (R. prowazeckii) 2. Epidemic relapsing fever ( B. recurrentis) 3. Trench fever (B. quintana)

Answer 171

1. Chlamydia 2. Rickettsia, Viruses

Answer 172

Crystal violet

Answer 173

1. Incubator set at: 35 +/- 2 C (MRSA cannot grow beyond 35C) 2. Content of 0.5 McFarland standard = 1% H2SO4, 1.175% BaCl2 3. Inoculum sizes a. Broth dilution = 5 x 10^5 CFU/ML b. Agar dilution = 1.0 x 10^4 CFU/ML c. Agar disk = 1.5 x 10^8 CFU/ML

Answer 174

1. Vancomycin 2. K. pneumoniae, E. coli 3. Aminoglycosides

Answer 175

1. Clostridium difficile / Clostridaloides 2. Coagglutination test 3. Propionibacterium acnes

Answer 176

Molecular technique

Answer 177

1. gm (+) bacteria 2. gm (+) bacteria 3. gm (-) cocci

Answer 178

1. S. pneumoniae 2. H. influenzae 3. Franciscella

Answer 179

1. C. diphtheriae 2. Neisseria (for confirmatory) 3. B. pertussis

Answer 180

1. L. pnuemophila 2. C. trachomatis 3. Brucella spp. 4. B. pertussis

Answer 181

1. Proteus 2. B-hemolytic strep 3. B. cepacia 4. Alkaligenes fecalis 5. C. violaceum

Answer 182

1. P. multocida 2. N. animaloris 3. C. difficile 4. S. maltophilia

Answer 183

Acute phase Specimens should be collected during the acute (early) phase of an illness (or within 2 to 3 days for viral infections) and before antibiotics are administered, if possible.

Answer 184

70% alcohol Wipe area with sterile saline or 70% alcohol.

Answer 185

Less than 15 minutes

Answer 186

BAP, CAP, THIO CSF BA, CA (Routine) BA, CA, thio (Shunt)

Answer 187

Less than 1 hour at room temperature

Answer 188

Cary-Blair medium

Answer 189

3 Collect three specimens every other day at a minimum for outpatients; hospitalized patients (inpatients) should have a daily specimen collected for 3 days; specimens from inpatients hospitalized more than 3 days should be discouraged.

Answer 190

Neisseria meningitidis

Answer 191

-20C Urine, stool, viral specimens, sputa, swabs, and foreign devices such as catheters should be stored at 4° C. Serum for serologic studies may be frozen for up to 1 week at –20°C, and tissues or specimens for long-term storage should be frozen at –70°C.

Answer 192

Nutritive and differential medium Blood agar is considered both a nutritive and differential medium because it differentiates organisms based on whether they are alpha (α)-, beta (β)-, or gamma (γ)- hemolytic.

Answer 193

3+ Numbers of organisms present can subse- quently be graded as 4+ (many, heavy growth) if growth is out to the fourth quadrant, 3+ (moderate growth) if growth is out to the third quadrant, 2+ (few or light growth) if growth is in the second quadrant, and 1+ (rare) if growth is in the first quadrant.

Answer 194

5 to 10% H2, 5 to 10% CO2, 80 to 90% N2, 0% O2 Anaerobes usually cannot grow in the presence of O2, and the atmosphere in anaerobe jars, bags, or chambers is composed of 5% to 10% hydrogen (H2), 5% to 10% CO2, 80% to 90% nitrogen (N2), and 0% O2.

Answer 195

Strict anaerobes In addition to amount of growth present, the location of growth within thioglycollate broth indicates the type of organism present based on oxygen requirements. Strict anaerobes will grow at the bottom of the broth tube, whereas aerobes will grow near the surface. Microaerophilic organisms will grow slightly below the surface where oxygen concentrations are lower than atmospheric concentrations. In addition, facultative anaerobes and aerotolerant organisms will grow throughout the medium, as they are unaffected by the variation in oxygen content.

Answer 196

Strict aerobes

Answer 197

Microaerophilic organisms

Answer 198

Facultative anaerobes

Answer 199

Differential media

Answer 200

Sulfonamides

Answer 201

Inhibits cell wall synthesis

Answer 202

Chloramphenicol

Answer 203

1.5 x 10 8th CFU/mL

Answer 204

1% sulfuric acid and 1.175% barium chloride

Answer 205

High (center of plate) to low (periphery of plate) Diffusion of the drug in the agar establishes a concentration gradient from high (center of plate) to low (periphery of plate).

Answer 206

D zone test

Answer 207

Staphylococcus spp. from Micrococcus spp. Staphylococci are susceptible to furazolidone, giving zones of inhibition that are 15 mm or greater. Micrococcus spp. are resistant to furazolidone, giving zones of 6–9 mm. The test is performed as a disk susceptibility procedure using a blood agar plate.

Answer 208

All of these The slide coagulase test using rabbit plasma with EDTA detects bound coagulase or “clumping factor” on the surface of the cell wall, which reacts with the fibrinogen in the plasma. This test is not positive for all strains of S. aureus, and a negative result must be confirmed by the tube method for detecting “free coagulase” or extracellular coagulase. The tube test is usually positive within 4 hours at 35°C; however, a negative result must then be incubated at room temperature for the remainder of 18–24 hours. Some strains produce coagulase slowly or produce fibrinolysin, which dissolves the clot at 35°C. Latex agglutination procedures utilize fibrinogen and IgG-coated latex beads that detect protein A on the staphylococcal cell wall.

Answer 209

Acetoin The production of acetoin by S. aureus from glucose or pyruvate differentiates it from S. intermedius, which is also coagulase positive. This test is also called the VP test. Acetoin production is detected by addition of 40% KOH and 1% α-naphthol to the VP test broth after 48 hours of incubation. A distinct pink color within 10 minutes denotes a positive test.

Answer 210

All of these S. epidermidis represents 50%–80% of all coagulase-negative Staphylococcus spp. recovered from numerous clinical specimens. It is of special concern in nosocomial infections because of its high resistance to antibiotics.

Answer 211

S. epidermidis

Answer 212

Novobiocin susceptibility S. epidermidis and S. saprophyticus are the two possibilities because they are both catalase positive, coagulase negative, urease positive, and ferment lactose. Novobiocin susceptibility is the test of choice for differentiating these two species. S. epidermidis is sensitive but S. saprophyticus is resistant to 5 μg of novobiocin.

Answer 213

Mannitol salt agar

Answer 214

Vancomycin MRSA isolates are usually tested for susceptibility or resistance to vancomycin, a glycopeptide.

Answer 215

Oxacillin Oxacillin is the drug used to screen staphylococci for resistance to antibiotics having the β-lactam ring. Included in this group are penicillin, cephalosporin, monobactam, and carbapenem. MRSA defines strains of staph that are resistant to all of these antibiotic groups. MRSA strains are treated with vancomycin or oxazolidinone.

Answer 216

Coagulase, glucose fermentation, DNase S. aureus is the cause of “scalded skin” syndrome in newborn infants. The production of a potent exotoxin (exfoliatin) causes the epidermis to slough off, leaving the newborn’s skin with a red, raw texture or a burned, scalded look.

Answer 217

Anti-streptolysin O

Answer 218

Bacitracin, CAMP, PYR Group B streptococci (S. agalactiae) are important pathogens and can cause serious neonatal infections. Women who are found to be heavily colonized vaginally with S. agalactiae pose a threat to the newborn, especially within the first few days after delivery. The infection acquired by the infant is associated with pneumonia.

Answer 219

Optochin, bile solubility, PYR S. pneumoniae colonies appear as α-hemolytic “donut” shaped colonies on 5% sheep blood agar. The mucoid colonies may appear “wet” or “watery” due to the capsule surrounding the organism. The Gram-stained smear reveals lancet-shaped gram-positive cocci in pairs surrounded by a clear area (the capsule). To differentiate the viridans streptococci from S. pneumoniae, the most appropriate test is the Optochin disk test. S. pneumoniae on blood agar are susceptible to Optochin but viridans streptococci are resistant.

Answer 220

Enterococcus faecalis

Answer 221

S. pneumoniae

Answer 222

Enterococcus faecalis Enterococcus (Streptococcus) faecalis is the cause of up to 20% of the bacterial endocarditis cases and is the most commonly encountered species in this condition.

Answer 223

Staphylococcal cross-streak test The staphylococcal streak, across the NVS inoculum, provides the nutrients needed. Very small colonies of NVS can be seen growing adjacent to the staphylococcal streak on the blood agar plate in a manner similar to the satellite phenomenon of Haemophilus spp. around S. aureus.

Answer 224

Hanging-drop motility (25°C) and catalase L. monocytogenes is catalase positive and displays a “tumbling” motility at room temperature. Streptococcus spp. are catalase-negative and nonmotile.

Answer 225

Culture specimens in ambient oxygens at 37C Cultures must be incubated in 3%–7% CO2 at 35°C. Cultures should be held a minimum of 48 hours before being considered negative.

Answer 226

Enterobacteriaceae from gastrointestinal specimens

Answer 227

MacConkey agar with sorbitol

Answer 228

Cefsulodin–Irgasan–Novobiocin (CIN) agar

Answer 229

Citrobacter freundii Biochemical differentiation is essential because Citrobacter isolates may give a false-positive agglutination test with Salmonella grouping sera. C. freundii strains, like Salmonella spp., are usually H2S producers and may be confused with Salmonella spp. unless the proper biochemical tests are utilized. C. freundii and Salmonella spp. are adonitol, indole, and malonate negative. However, C. freundii is KCN positive, whereas Salmonella spp. are KCN negative.

Answer 230

Campylobacter spp. Shigella spp. and Campylobacter spp. are both causes of diarrhea, abdominal pain, fever, and sometimes vomiting. Blood is present in the stools of patients infected with Shigella as a result of invasion and penetration of the bowel. Young children may also exhibit bloody stools when infected with Campylobacter.

Answer 231

Yersinia pestis

Answer 232

Inhalation of contaminated airborne droplets Bubonic plague involves an inflammatory swelling of the lymph nodes of the axilla and groin, whereas pneumonic plague is associated with an airborne route involving the lungs. Both infections are caused by the same member of the Enterobacteriaceae family, Yersinia pestis.

Answer 233

Indole, phenylalanine deaminase, and urease A swarmer on blood agar would most likely be a Proteus spp. A lactose nonfermenter and swarmer that is often isolated from urinary tract infections is P. mirabilis.

Answer 234

Acinetobacter spp. Acinetobacter spp. are plump coccobacilli that tend to resist alcohol decolorization; they may be mistaken for Neisseria spp.

Answer 235

Requirement of 5 to10% CO2 for growth The HACEK group of organisms are gram negative bacilli that require increased CO2 for growth. They are commonly associated with endocarditis and include Haemophilus species (especially H. aprophilus), Actinobacillus actinomycetemcomitans, Cardiobacterium hominis, Eikenella corrodens and Kingella species.

Answer 236

Growth at 42ºC Pseudomonas aeruginosa grows at 42˚C but this temperature is inhibitory for other Pseudomonas species.

Answer 237

Pseudomonas aeruginosa Pseudomonas aeruginosa is a major cause of nosocomial pneumonia in health-care related settings. A major portion of the P. aeruginosa associated nosocomial pneumonia occurs in immunocompromised patients in intensive care units who have undergone intubation (ventilator-associated pneumonia). Among the conditions that predispose immunocompromised patients to P. aeruginosa infection is the utilization of contaminated respiratory equipment during intubation. P. aeruginosa is a gram-negative, oxidase positive, obligate aerobe that produces numerous extracellular virulence factors including exotoxins, proteases, and rhamnolipid.

Answer 238

Pseudomonas aeruginosa P. aeruginosa is often recovered from the respiratory secretions of cystic fibrosis patients. If the patient is chronically infected with the mucoid strain of P. aeruginosa, the biochemical identification is very difficult. The mucoid strain results from production of large amounts of alginate, a polysaccharide that surrounds the cell.

Answer 239

Pseudomonas aeruginosa The oxidase test, as well as growth at 42°C, distinguish P. aeruginosa from the other pseudomonads listed, particularly B. cepacia, which is also associated with cystic fibrosis.

Answer 240

Pseudomonas aeruginosa Cetrimide (acetyl trimethyl ammonium bromide) agar is used for the isolation and identification of P. aeruginosa.

Answer 241

Pseudomonas aeruginosa Swimmer's ear is a form of external otitis common to persons who swim and fail to completely dry their ear canals when they get out of the water. The organism most commonly associated with this condition is Pseudomonas aeruginosa. It is an organism known to be an opportunistic pathogen and one that favors a watery environment.

Answer 242

Stenotrophomonas sp. Stenotrophomonas maltophilia Large, smooth, glistening colonies with uneven edges and lavender-green to light purple pigment; greenish discoloration underneath growth; ammonia smell

Answer 243

Stenotrophomonas maltophilia S. maltophilia is the third most frequently isolated nonfermentative gram-negative rod in the clinical laboratory. Cystic fibrosis patients are at greater risk for infections because of previous antimicrobial treatment and recurrent pneumonia and because some strains may be colonizers.

Answer 244

Synthesis of hemin The porphyrin test is an alternative method for detecting heme- producing species of Haemophilus. It detects whether or not the organism converts the substrate delta-aminolevulinic acid into porphyrins or porphobilinogen which are intermediates for the synthesis of X factor.

Answer 245

H. ducreyi Chancroid is the sexually transmitted disease caused by H. ducreyi. The initial symptom is the development of a painful genital ulcer and inguinal lymphadenopathy.

Answer 246

Chancroid Haemophilus ducreyi is the causative agent of chancroid, a serious sexually transmitted disease. The disease is more prevalent in the tropics than in temperate parts of the world. The bacteria produce buboes in the groin and can cause a septicemia.

Answer 247

Haemophilus influenzae Haemophilus influenzae is a gram-negative bacillus. In young children, it can cause pneumonitis, sinusitis, otitis, and meningitis. Occasionally, it produces a fulminative laryngotracheitis with such severe swelling of the epiglottis that tracheostomy becomes necessary. Clinical infections with this organism after the age of 3 years are less frequent, especially since approval of the type b vaccine.

Answer 248

Type b H. influenzae type b (Hib) is most commonly encountered in serious infections in humans.

Answer 249

Haemophilus influenzae "Satellitism" is the name given to the appearance of colonies of Haemophilus influenzae on sheep blood agar medium around colonies of organisms that provide an essential growth factor. H. influenzae requires both hemin and NAD. Colonies of some organisms, such as Staphylococcus and Neisseria, produce NAD, which diffuses into the surrounding agar and enables H. influenzae to grow.

Answer 250

Aggregatibacter Haemophilus aphrophilus and Haemophilus paraphrophilus have been reclassified as a single species based on multilocus sequence analysis. Aggregatibacter aphrophilus now includes both the hemin-dependent and hemin-independent isolates.

Answer 251

Aggregatibacter aphrophilus H. aphrophilus is the only species that does not require X or V factors. H. aphrophilus is an uncommon cause of endocarditis and is the H member of the HACEK group of bacteria associated with slowly progressive (subacute) bacterial endocarditis.

Answer 252

Thiosulfate citrate bile salts sucrose medium V. cholerae as well as other vibrios, including V. parahaemolyticus and V. alginolyticus, are isolated best on thiosulfate citrate bile salts sucrose medium, although media such as mannitol salt agar also support the growth of vibrios. Maximal growth occurs at a pH of 8.5 to 9.5 and at 37°C incubation.

Answer 253

Vibrio cholerae The toxin of V. cholerae and LT enterotoxin from E. coli are similar. Cyclic AMP is increased, as is fluid and electrolyte release from the crypt cells into the lumen of the bowel. Watery, profuse diarrhea ensues.

Answer 254

Campylobacter jejuni Most Campylobacter species grow best under lower oxygen tension in an atmosphere of 5% oxygen, 10% carbon dioxide and 85% nitrogen. E. coli and Proteus mirabilis are facultative anaerobes and Pseudomonas is an aerobe.

Answer 255

Skirrow medium Skirrow medium is an enriched selective blood agar medium used for the isolation of Campylobacter from specimens with mixed flora.

Answer 256

42C Campylobacter jejuni/coli grow better at 42˚C than 37˚C and other organisms in the colon are inhibited at this high temperature.

Answer 257

Subculture the bottle, and incubate in microaerophilic conditions

Answer 258

Guillain-Barré syndrome Most recently, postinfectious complications with C. jejuni have been recognized and include reactive arthritis and Guillain-Barré syndrome, an acute demyelination (removal of the myelin sheath from a nerve) of the peripheral nerves.

Answer 259

Campylobacter jejuni

Answer 260

Helicobacter pylori Helicobacter pylori was first recognized as a possible cause of gastritis and peptic ulcer. This organism is readily isolated from gastric biopsies but not from stomach contents. It is similar to Campylobacter species and grows on chocolate agar at 37°C in the same microaerophilic environment suitable for C. jejuni (Campy-Pak or anaerobic jar [Gas Pak] without the catalyst). H. pylori, however, grows more slowly than C. jejuni, requiring 5 to 7 days incubation. C. jejuni grows optimally at 42°C, not 37°C, as does H. pylori.

Answer 261

Urea broth Helicobacter pylori produce large amounts of extracellular urease and are positive for urea within 2 hours.

Answer 262

Bordetella pertussis B. pertussis, the primary pathogen of whooping cough, uses several mechanisms to overcome the immune defenses of healthy individuals.

Answer 263

Nasopharyngeal swab Posterior nasopharyngeal cultures are recommended for the recovery of Bordetella pertussis in suspected cases of pertussis (whooping cough). Swabs of the nasopharynx are inoculated on the selective agar Regan-Lowe. Cephalexin is added to the culture medium to inhibit the growth of contaminating indigenous flora.

Answer 264

Regan-Lowe agar Regan-Lowe agar is an enriched and selective medium for the isolation of Bordetella pertussis. Cephalexin is added to inhibit nasopharyngeal flora. It provides better isolation of Bordetella pertussis than Bordet-Gengou medium.

Answer 265

Bordetella pertussis Bordetella pertussis is the etiologic agent of pertussis, or whooping cough. On Bordet-Gengou or Regan-Lowe agars, the organism forms small, round colonies that resemble mercury droplets. A nasopharyngeal swab is recommended as the optimal specimen for the recovery of this agent.

Answer 266

Rapid hydrolysis of urea Both organisms are oxidase positive; Bordetella bronchiseptica is urea positive within 4 hours.

Answer 267

Brucella melitensis Brucella are small, aerobic, Gram-negative coccobacilli. Of the four well-characterized species of Brucella, only one—B. melitensis—characteristically infects both goats and humans. Brucellosis may be associated with gastrointestinal and neurologic symptoms, lymphadenopathy, splenomegaly, hepatitis, and osteomyelitis.

Answer 268

Brucellosis Brucella infects cattle and may be transmitted to humans by the ingestion of contaminated milk or other dairy products. Milk is able to support the growth of many clinically significant microorganisms, which may often be ingested in unpasteurized dairy products.

Answer 269

Charcoal and yeast extract Buffered Charcoal yeast extract medium is as specialized enrichment medium for the isolation of Legionella. The nutritive base includes yeast extract. Charcoal is added to the medium as detoxifying agent.

Answer 270

Bronchial washings Tissue samples from the lower respiratory tract (lung biopsy) have the greatest yield of positive cultures for Legionella pneumophila. However, these specimens require invasive procedures and are not commonly performed. Cultures of lower respiratory tract specimens, such as bronchial wash and expectorated sputum, are appropriate for the isolation of L. pneumophila.

Answer 271

Cystine glucose blood agar Francisella tularensis is fastidious and not readily recovered in culture. Cysteine blood glucose agar is an enriched medium with beef heart infusion, peptones, glucose and rabbit blood. It also includes cystine, which is required by F. tularensis for growth.

Answer 272

Francisella tularensis Francisella tularensis requires cysteine or cystine for growth. Glucose-cysteine with thiamine and cystine heart media are commercially available for suspected cases of tularemia.

Answer 273

Pasteurella multocida Pasteurella (gram-negative coccobacilli) are primarily animal pathogens, but they can cause a wide range of human diseases. Pasteurella multocida occurs worldwide in domestic and wild animals. It is the most common organism in human wounds inflicted by bites of cats and dogs. It is a common cause of hemorrhagic septicemia in a variety of animals. Wounds commonly present with an acute onset (within hours) of redness, swelling, and pain.

Answer 274

Liver cirrhosis P. multocida subsp. multocida is most commonly encountered in clinical specimens. Reported virulence factors for this subspecies include lipopolysaccharide, cytotoxin, six serotypes of the antiphagocytic capsule, surface adhesins, and iron-acquisition proteins. Other manifestations of infection by P. multocida subsp. multocida can include respiratory disease and systemic disease such as endocarditis and septicemia. Liver cirrhosis is viewed as a risk factor for systemic disease.

Answer 275

Gardnerella vaginalis Clue cells: epithelial cells with Gardnerella bacteria attached

Answer 276

Haverhill fever Streptobacillus moniliformis is a gram-negative bacillus that requires media containing blood, serum, or ascites fluid as well as incubation under carbon dioxide (CO2) for isolation from clinical specimens. This organism causes rat-bite fever and Haverhill fever in humans. When S. moniliformis is acquired by ingestion, the disease is called Haverhill fever.

Answer 277

Cystine Streptobacillus moniliformis is a gram-negative bacillus that requires media containing blood, serum, or ascites fluid as well as incubation under carbon dioxide (CO2) for isolation from clinical specimens. This organism causes rat-bite fever and Haverhill fever in humans.

Answer 278

Chromobacterium violaceum Chromobacterium violaceum is a motile, gram-negative bacillus found in soil and water that can be pathogenic for humans. The production of a non-water-soluble violet pigment by these organisms aids in their identification

Answer 279

Chryseobacterium Chryseobacterium spp. are ubiquitous in the environment and are especially associated with moist soil and water. Chryseobacterium (formerly Flavobacterium) meningosepticum, a known nosocomial pathogen, has been implicated in outbreaks of meningitis in hospitals and is associated with the use of contaminated respiratory therapy equipment.

Answer 280

Capnocytophaga Capnocytophaga spp. are fermentative gram-negative bacteria that inhabit the oral cavity of humans. These organisms have been identified as a cause of disease in the oral cavity, and in compromised hosts they have been implicated in systemic disease isolated from cerebrospinal fluid, pleural fluid, and pulmonary secretions. The gliding motility is best observed during the log phase of growth and can be demonstrated by darkfield microscopy and on sheep blood agar by the production of concentrically spreading growth around primary colonies.

Answer 281

Bacillus anthracis Bacillus anthracis are large rectangular gram positive bacilli that produces colonies with an irregular edge (often described as Medusa-head appearance) on blood agar. Colonies are non hemolytic, catalase positive and non motile.

Answer 282

Nonhemolytic and nonmotile B. ANTHRACIS: NONMOTILE AND NONHEMOLYTIC B. CREAUS: MOTILE AND BETA-HEMOLYTIC

Answer 283

Woolsorters’ disease Bacillus anthracis Causative agent of anthrax, of which there are three forms: 1. Cutaneous anthrax occurs at site of spore penetration 2 to 5 days after exposure and is manifested by progressive stages from an erythematous papule to ulceration and finally to formation of a black scar (i.e., eschar); may progress to toxemia and death 2. Pulmonary anthrax, also known as woolsorters’ disease, follows inhalation of spores and progresses from malaise with mild fever and nonproductive cough to respiratory distress, massive chest edema, cyanosis, and death 3. Gastrointestinal anthrax may follow ingestion of spores and affects either the oropharyngeal or the abdominal area; most patients die from toxemia and overwhelming sepsis

Answer 284

Bacillus anthracis Bacillus anthracis infects humans by three routes: respiratory, gastrointestinal, and cutaneous. Malignant pustule is the name given to lesions seen in cutaneous anthrax in humans.

Answer 285

Food poisoning Bacillus cereus is of particular interest as an etiologic agent of human cases of food poisoning. This enterotoxin-producing microorganism is most commonly associated with cases of food poisoning following ingestion of reheated rice served at Asian restaurants.

Answer 286

Clostridium and Bacteroides spp. ETHANOL SHOCK SPORE ISOLATION Clostridium species can be recovered from mixed populations of organisms and identified using the ethanol shock spore technique. Ethanol treatment of samples should result in the killing of all vegetative microorganisms. However, clostridial endospores may be resistant to ethanol, and after ethyl alcohol treatment, the spores will germinate upon inoculation and proper incubation on anaerobic blood agar in anaerobic conditions.

Answer 287

Clostridium tetani Corynebacterium species and Propionibacterium species do not produce spores and Bacillus is an aerobic organism.

Answer 288

Clostridium perfringens The reverse CAMP test, production of lecithinase and demonstration of double zone of hemolysis are tests and characteristics used for the identification of Clostridium perfringens.

Answer 289

C. perfringens Clostridium perfringens is the species most commonly associated with clostridial myonecrosis or gas gangrene. These soil and water saprophytes most frequently gain entrance to the human body through traumatic wounds.

Answer 290

Ingestion of a neurotoxin Clostridium botulinum growing in food produces a potent neurotoxin that causes diplopia, dysphagia, respiratory paralysis, and speech difficulties when ingested by humans. The toxin is thought to act by blocking the action of acetylcholine at neuromuscular junctions. Botulism is associated with high mortality; fortunately, C. botulinum infection in humans is rare.

Answer 291

Botulinum toxin Botulinal toxin is the most potent exotoxin known. When absorbed, this exotoxin produces the paralyzing disease botulism. Toxin acts in the body by blocking the release of acetylcholine in the neuromuscular junction of the peripheral nervous system, causing muscle paralysis.

Answer 292

Clostridium difficile Patients treated with antibiotics develop diarrhea that, in most cases, is self-limiting. However, in some instances, particularly in those patients treated with ampicillin or clindamycin, a severe, life-threatening pseudomembranous enterocolitis develops. This disease has characteristic histopathology, and membranous plaques can be seen in the colon by endoscopy. Pseudomembranous enterocolitis and antibiotic-associated diarrhea are caused by an anaerobic Gram-positive rod, Clostridium difficile.

Answer 293

Assays to detect toxin in stool The most rapid and accurate diagnostic method is detecting toxins A and/or B in stool specimens. Cycloserine-cefoxitin-fructose agar (CCFA) is the recommended selective medium for C. difficile, although few laboratories attempt isolation.

Answer 294

Clostridium difficile CCFA is used for recovery of C. difficile from stool cultures. Cycloserine and cefoxitin inhibit growth of gram-negative coliforms in the stool specimen. C. difficile ferments fructose, forming acid that, in the presence of neutral red, causes the colonies to become yellow.

Answer 295

Corynebacterium diphtheriae C. diphtheriae must be recovered from the deep layers of the pseudomembrane that forms in the nasopharyngeal area. A flexible calcium alginate nasopharyngeal swab is the best choice for collecting a specimen from the posterior nares and pharynx.

Answer 296

Potassium tellurite Media containing potassium tellurite is used for the recovery of Corynebacterium diphtheriae.

Answer 297

A positive toxigenicity test In order to determine if an isolate of Corynebacterium diphtheriae produces toxin, testing for the presence of diphtheria toxin must be performed using methods such as Elek test or PCR.

Answer 298

L. monocytogenes L. monocytogenes can be presumptively identified by observation of motility by direct wet mount. The organism exhibits characteristic end-over-end tumbling motility when incubated in nutrient broth at room temperature for 1 to 2 hours. Alternatively, characteristic motility can be seen by an umbrella-shaped pattern that develops after overnight incubation at room temperature of a culture stabbed into a tube of semisolid agar.

Answer 299

Listeria monocytogenes Listeria multiplies both extra-cellularly and intracellularly, but under most circumstances, a competent immune system eliminates Listeria. As expected, listeriosis is seen in the very young and the very old, and in people with compromised immune systems. Reports of Listeria food outbreaks have implicated such foods as coleslaw and milk products, especially if not pasteurized. Early-onset-syndrome listeriosis is the result of infection in utero and characterized by sepsis and lesions in multiple organs.

Answer 300

Feta cheese The general population should always properly wash raw vegetables and thoroughly cook vegetables and meat to prevent listerosis. Patients who are immunocompromised and pregnant women should avoid eating soft cheeses (e.g., Mexican-style cheese, feta, brie, Camembert, and blue-veined cheese) to prevent food-borne listeriosis. Additionally, leftover or ready-to-eat foods such as hot dogs or cold cuts should be thoroughly heated before consumption and stored for only a short period before disposal, because L. monocytogenes is able to replicate during refrigeration at 4°C.

Answer 301

Erysipelothrix sp. Erysipelothrix sp. is the only catalase-negative, gram-positive non-spore-forming rod that produces hydrogen sulfide (H2S) when inoculated into triple sugar iron (TSI) agar.

Answer 302

C. Capnocytophaga - fusiform, gliding motility Cardiobacterium hominis - HACEK GM(-) bacillus in TEARDROP forms (singles, pairs or rosettes) Kingella spp. - Square end Aggregatibacter aphrophilus - foam loving

Answer 303

B. Gram stain

Answer 304

Shigella 'CPON'

Answer 305

Salmonella 'SPACE'

Answer 306

E. cloacae

Answer 307

S. aureus - Golden Yellow

Answer 308

Group D strep. Enterococci

Answer 309

D. P. mirabilis

Answer 310

Group A Strep Taxo A

Answer 311

B. C C. freundii = LDC - KCN + 70% urease + Salmonella = LDC + KCN - Urease -

Answer 312

C. Urease test PCR Stool antigen test (immunochromatography, EIA) Urea breath test - 13C --> CO2 using Scintillation counter/ Spectrophotometer = detect radio labelled carbon

Answer 313

A. Pseudomonas

Answer 314

B. S. pyogenes B. S. pyogenes

Answer 315

B. Xenopsylla cheopsis

Answer 316

E. rhusiopathiae

Answer 317

H. ducreyi H. influenza = Xylose +

Answer 318

N. meningitidis H. influenzae B. pertussis MRSA

Answer 319

Cholera-like toxin: ETEC Shiga/ shigella-like toxin: EHEC Shigella-like infection: EIEC

Answer 320

1. Providencia stuartii 2. Klebsiella and Salmonella typhi

Answer 321

1. Plesiomonas 2. Pantoea agglomerans 3. Serratia - DNase, Lipase, Gelatinase

Answer 322

1. Salmonella 2. S. typhi 3. M. bovis 4. Typhoid Mary Mallon

Answer 323

1. Proteus spp. 2. Clostridium septicum

Answer 324

Salmonella Proteus Arizonae C. freundii E. tarda

Answer 325

1. M. tuberculosis 2. Y. pestis

Answer 326

Burkholderia pseudomallei Aggregatibacter actinomycetemcomitans Yersinia

Answer 327

1. Y. enterolitica (children) 2. Y. enterolitica (1-6C)

Answer 328

1. V. parahaemolyticus 2. Rotavirus (children), Norwalk (adults) 3. Campylobacter, Helicobacter

Answer 329

P. aeruginosa

Answer 330

1. P. aeruginosa 2. B. cepacia 3. Stenotrophomonas

Answer 331

1. Acinetobacter baumanni 2. Acanthamoeba 3. P. aeruginosa 4. C. violaceum 5. S. maltophilia

Answer 332

1. Candida albicans 2. H. influenzae 3. S. pneumoniae 4. H. influenzae

Answer 333

1. Horse blood 2. Haemophilus 3. S. granulicatella and S. abotrophia

Answer 334

1. Cardiobacterium hominis 2. Plasmodium malariae

Answer 335

1. Klebsiella ganulomatis 2. Chlamydia trachomatis

Answer 336

1. Pasteurella multocida 2. Bartonella henselai, Alfipia felis 3. S. intermedius, S. hyicus 4. E. corrodens

Answer 337

1. Proteus 2. C. tetani, C. septicum 3. Demonstration of toxin 4. Staphylococxal enterotoxin

Answer 338

1. Beffati 2. Amycolatum

Answer 339

1. Erysipelothrix rhusiopathiae 2. Streptococcus pyogenes 3. Corynebactwerium minutissimum

Answer 340

Lactobacillus, E.coli, Listeria

Answer 341

1. G. vaginalis (Bacterial vaginosis) 2. T. vaginalis 3. Candidiasis (summer disease, vulvovaginitis)

Answer 342

PCR (GeneXpert) Sputum spx

Answer 343

1. P. aeruginosa 2. Schistosoma (Schistosomule stage) 3. Mycobacterium marinum

Answer 344

1. Vibrio 2. Aeromonas 3. Legionella (parasite of parasites), Naegleria 4. M. gordonae

Answer 345

Shigella Eikenella corrodens M. ulcerans

Answer 346

Nocardia asteroides (bacteria) Histoplasma capsulatum (fungi) Paragonimus westermani (parasite)

Answer 347

1. C. diphtheriae 2. M. leprae 3. Nocardia, Streptomyces, Nocardiopsis

Answer 348

1. Borrelia 2. Treponema 3. Leptospira interrogans, Leptospira biflexa

Answer 349

1. Motile without flagella 2. C. jejuni, C. pneumoniae, Zika virus 3. Culture

Answer 350

1. Dicks, Schultz-Charlton 2. Francis 3. Schick's 4. Lepromin 5. Mantoux 6. Frei's

Answer 351

1. To drive off oxygen 2. Colorless

Answer 352

1+ Faint 2+ Apple green 3+ Bright 4+ Brillant

Answer 353

GeneXpert MDR-TB common in HIV pxs

Answer 354

Lipids Mycobacteria characteristically possess a high lipid content, unlike gram-positive cocci and gram-negative bacteria. The high lipid content acts to protect these organisms from dehydration and the lethal effects of alkali, various germicides, alcohol, and acids. Thus, these bacteria do not stain well with the Gram stain, and an acid-fast staining technique must be used.

Answer 355

N-glycolylmuramic acid and an increase in lipid content Mycobacterium spp. have an unusual cell wall structure. The cell wall contains N-glycolylmuramic acid instead of N-acetylmuramic acid, and it has a very high lipid content, which creates a hydrophobic permeability barrier.

Answer 356

PPD test A positive tuberculin skin test reaction is an example of a hypersensitivity reaction. Tuberculin preparations are prepared from culture filtrates, which are precipitated with trichloroacetic acid and are known as purified protein derivative (PPD). A positive test demonstrates an area of induration following an intradermal injection of PPD.

Answer 357

Sputum The mycobacteria are only slightly more resistant to the decontamination procedures than other bacteria. Therefore, it is only appropriate to decontaminate specimens for mycobacteria that are contaminated with normal flora. Because sputum passes through the oral cavity, it contains a large amount of normal oral flora.

Answer 358

Löwenstein-Jensen (L-J) medium Commonly used medium; good recovery of M. tuberculosis but poor recovery of many other species; M. genovense fails to grow

Answer 359

Chocolate agar Lowenstein-Jensen, Lowenstein-Jensen-Gruft, and Middlebrook media are commonly used for the isolation of the mycobacteria. Chocolate agar will support the growth of Mycobacterium haemophilium; however, chocolate agar is not routinely used for cultures of mycobacteria.

Answer 360

Mycobacterium tuberculosis A serpentine pattern of growth indicates production of cording factor, a virulence factor for M. tuberculosis. M. tuberculosis is positive for niacin accumulation, while the other three species are niacin negative.

Answer 361

M. tuberculosis The human tubercle bacillus is Mycobacterium tuberculosis. Growth of this well-known human pathogen appears in 2 to 3 weeks when incubated at 35°C. These niacin-positive mycobacteria form dry heaping colonies that are buff colored.

Answer 362

Niacin and nitrate reduction tests M. tuberculosis: Positive for niacin and nitrate reduction M. bovis: Negative for niacin and nitrate reduction

Answer 363

Kinyoun stain Acid-fast bacilli can be demonstrated in stained smears of clinical material using the Ziehl-Neelsen or Kinyoun acid-fast stains. The Kinyoun carbol-fuchsin method uses a higher concentration of phenol in the primary stain to accelerate the staining process. Therefore, unlike the Ziehl-Neelsen stain, the Kinyoun stain does not need to be heated.

Answer 364

300 oil immersion fields Before an acid-fast smear is reported as negative, it should be examined carefully by scanning at least 300 oil immersion fields (magnification ×1000), equivalent to three full horizontal sweeps of a smear that is 2 cm long and 1 cm wide.

Answer 365

Bright red rods against a blue background The carbolfuchsin (fuchsin with phenol) stains the mycobacteria red and does not decolorize after the acid–alcohol is added. The background and any other bacterial elements will decolorize and are counterstained blue by the methylene blue.

Answer 366

Auramine-rhodamine Auramine-rhodamine is a fluorescent stain used to visualize the mycobacteria. The bacteria retain the stain and will appear bright yellow against a black background. Because it is easier to see the bacilli, this stain is more sensitive than a fuschin-based stain (e.g., Ziehl-Neelsen).

Answer 367

Kanamycin Rapid development of drug resistance is a concern in the treatment of tuberculosis. Patients are treated generally with a combination of at least two of the primary drugs, such as isoniazid, rifampin, ethambutol, and pyrazinamide. Because of the slowly growing nature of the bacteria, they are innately resistant to a number of agents.

Answer 368

Mycobacterium leprae Hansen disease (leprosy) is caused by Mycobacterium leprae. Cultures of this agent on artificial media, unlike other mycobacteria, have not been successful. Cultivation can be accomplished by injecting bacilli into the foot pads of mice or systemically into armadillos.

Answer 369

M. gordonae Mycobacterium gordonae has been recovered from water stills, faucets, and bodies of water in nature, which is why it has been called the "tap water scotochromogen." These organisms are not considered to be pathogenic for humans, but because they may be recovered as contaminants, their identification is recommended.

Answer 370

M. marinum Mycobacterium marinum is the causative agent of "swimming pool granuloma.

Answer 371

Mycobacterium avium complex Immunocompromised patients, particularly those infected with HIV, can have disseminated mycobacterial infection; most of these infections are caused by M. avium complex.

Answer 372

Mycobacterium scrofulaceum Mycobacterium scrofulaceum is defined as a scotochromogen because of its characteristic of producing pigmentation in the dark. This slowly growing Mycobacterium is a cause of cervical adenitis and other types of infections predominantly in children. Therapy may require susceptibility studies that include the secondary drugs, because the organism is known in some cases to be resistant to isoniazid and streptomycin.

Answer 373

M. chelonei The MacConkey agar used for mycobacteria identification is a different formulation than that used for enterics, in that crystal violet is omitted. A MacConkey agar plate is inoculated with a 7-day broth culture of the test organism. The inoculated plate is then incubated at 37°C. Plates are checked for growth at 5 days, and if no growth is detected, they are checked daily until day 11, at which time they are discarded as negative. M. fortuitum and M. chelonei are the only mycobacteria able to grow on MacConkey agar in 5 days.

Answer 374

M. chelonei The MacConkey agar used for mycobacteria identification is a different formulation than that used for enterics, in that crystal violet is omitted. A MacConkey agar plate is inoculated with a 7-day broth culture of the test organism. The inoculated plate is then incubated at 37°C. Plates are checked for growth at 5 days, and if no growth is detected, they are checked daily until day 11, at which time they are discarded as negative. M. fortuitum and M. chelonei are the only mycobacteria able to grow on MacConkey agar in 5 days.

Answer 375

M. paratuberculosis M. paratuberculosis is known to cause an ulcerative intestinal disease with chronic diarrhea in cattle known as Johne’s disease. While M. paratuberculosis has been isolated from the intestines of humans with Crohn’s disease, the organism has not yet been proven to cause ileitis in humans.

Answer 376

M. bovis The T2H test differentiates M. tuberculosis from M. bovis. M. tuberculosis is not inhibited by T2H.

Answer 377

M. bovis Mycobacterium bovis is susceptible to 5 ug/mL of thiophene-2-carboxylic acid hydrazide (T2H). This Mycobacterium is associated with cattle and is rarely isolated from humans in the U.S. Growth occurs only at 35°C and is differentiated from other mycobacteria by its susceptibility to T2H.

Answer 378

Nocardia spp. Nocardia spp. should be suspected if colonies that are partially acid fast by the traditional method are positive with the modified acid-fast method using Kinyoun stain and 1% sulfuric acid as the decolorizing agent.

Answer 379

All of the above If the modified acid-fast stain results are positive, the isolate is a probable partially acid-fast aerobic actinomycete (i.e., Nocardia, Rhodococcus, Tsukamurella, or Gordonia sp).

Answer 380

Mycetoma Infection caused by the non–acid-fast aerobic actinomycetes is usually associated with chronic, granulomatous lesions of the skin referred to as mycetomas. Mycetoma is an infection of subcutaneous tissues that results in tissue swelling and drainage of the sinus tracts.

Answer 381

Nocardia sp.

Answer 382

N. asteroides Infections caused by Nocardia spp. can occur in immunocompetent and immunocompromised individuals. N. asteroides, N. brasiliensis, and N. otitidiscaviarum are the major causes of these infections, with N. asteroides causing greater than 80% of infections.

Answer 383

Actinomyces spp. Direct examination and the macroscopic presence in purulent exudate of “sulfur granules,” which reveal gram-positive filaments when crushed, is diagnostic for an infection with Actinomyces spp.

Answer 384

Actinomyces israelii LOCK JAW: C. tetani LUMPY JAW: Actinomyces

Answer 385

Sodoku Spirillum minus also causes rat-bite fever in humans and is referred to as sodoku. The clinical signs and symptoms are similar to those caused by Streptobacillus moniliformis, except that arthritis is rarely seen in patients with sodoku and swollen lymph nodes are prominent; febrile episodes are also more predictable in sodoku.

Answer 386

Serological analysis Serological tests of the patient’s serum for evidence of syphilis are routinely performed, but culturing is not because research animals must be used for inoculation of the suspected spirochete. T. pallidum does not stain by either the Gram or acid-fast technique.

Answer 387

Syphilis Cardiolipin is a tissue lipid produced as a byproduct of treponemal infection. Nontreponemal tests for syphilis take advantage of antibodies made to cardiolipin. The most commonly used tests are the rapid plasma reagin (RPR) for serum and the Venereal Disease Research Laboratory (VDRL) for cerebrospinal fluid.

Answer 388

Treponema pallidum subsp. pallidum Hutchinson's triad: a triad of symptoms that comprises Hutchinson's (notched) teeth, interstitial keratitis, and deafness and occurs in children with congenital syphilis Syphilis is caused by Treponema pallidum subsp. pallidum. Congenital syphilis occurs when a pregnant woman has a septicemia, and the spirochetes cross the placenta and infect the fetus. Infection can affect fetal development and cause premature birth or fetal death, or the pregnancy may go to term. Following in utero infection, the infant is most often born with lesions characteristic of secondary syphilis; perinatal death is not an uncommon consequence of infection.

Answer 389

Culturing of blood Leptospira spp. are most reliably detected during the first week of illness by the direct culturing of a blood sample. The media of choice are Fletcher semisolid and Stuart liquid medium, both of which are supplemented with rabbit serum.

Answer 390

Lice The human body louse, Pediculus humanus, is the vector for Borrelia recurrentis. Pathogenic species not only have specific vectors but also well-defined geographical distributions.

Answer 391

Lyme disease Lyme disease was first described in 1975 following an outbreak in Lyme, Connecticut. The etiologic agent, Borrelia burgdorferi, is transmitted to humans by the tick vector Ixodes dammini. Clinically the disease peaks in the summer and produces an epidemic inflammatory condition characterized by skin lesions, erythema, headache, myalgia, malaise, and lymphadenitis.

Answer 392

Borrelia spp. Borrelia spp. are often seen on Wright’s-stained smears of peripheral blood as helical bacteria with 3–10 loose coils. They are gram negative but stain well with Giemsa’s stain.

Answer 393

Inclusion conjunctivitis

Answer 394

Inclusion conjunctivitis Chlamydia trachomatis is the causative agent of inclusion conjunctivitis, trachoma, and genital tract infections, including lymphogranuloma venereum.

Answer 395

Chlamydia trachomatis Chlamydia trachomatis, a leading cause of blindness, can be detected in corneal scrapings of suspected cases of trachoma and inclusion conjunctivitis.

Answer 396

L1 C. trachomatis serovars L1, L2, L2b, and L3 are invasive causing LGV, in contrast to C. trachomatis serovars A-K, leaving the mucosa to spread to the regional lymph nodes.

Answer 397

Chlamydia psittaci C. psittaci is an endemic pathogen of all bird species. Psittacine birds (e.g., parrots, parakeets) are a major reservoir for human disease, but outbreaks have occurred among turkey-processing workers and pigeon aficionados. The birds may show diarrheal illness or may be asymptomatic. Humans acquire the disease by inhalation of aerosols.

Answer 398

Avians Human infections with Chlamydiophila psittaci (psittacosis) occur after exposure to infected birds and their droppings. A true zoonosis, psittacosis is a disease of birds that may be contracted by humans.

Answer 399

Mycoplasma pneumoniae Mycoplasma pneumoniae causes primary atypical pneumonia. The pneumonia is atypical in that it is milder than the pneumonia caused by Streptococcus pneumoniae.

Answer 400

SP4 agar Provided that arginine is added for Mycoplasma hominis, SP4 agar or broth can be used for the growth of M. pneumoniae and M. hominis.

Answer 401

Mycoplasma hominis When grown on culture media, colonies, most notably M. hominis, are said to have a "fried egg" appearance because the central portion of the colony has grown into the agar and thus appears more dense and is slightly raised.

Answer 402

Mycoplasma pneumoniae Mycoplasma hominis, M. genitalium, and Ureaplasma urealyticum have been linked to human genital infections. These species can also be isolated from asymptomatic sexually active adults. M. pneumoniae is primarily a respiratory tract pathogen.

Answer 403

Fever, headache, and rash Rickettsias are suspected when the triad of fever, headache, and rash is the primary clinical manifestation in patients with an exposure to insect vectors. Infections caused by these organisms may be severe and are sometimes fatal.

Answer 404

Rickettsia rickettsii R. rickettsii Rocky Mountain spotted fever Vector: ticks (Dermacentor spp.)

Answer 405

Chiggers O. tsutsugamushi Scrub typhus Vector: chiggers

Answer 406

Brill-Zinsser disease Humans who have had the classic form of typhus may remain infected with the causative agent Rickettsia prowazekii. Relapses or recrudescence of disease may occur in these persons years or decades after the initial attack. The latent form of infection is known as Brill-Zinsser disease and may serve as an interepidemic reservoir for epidemic typhus.

Answer 407

Rickettsia typhi Murine typhus is transmitted to humans by fleas infected with Rickettsia typhi. Prevalent in the southern U.S., it is primarily a disease of rodents and is sometimes transmitted to humans. Control of disease outbreaks is related to rodent (rat) control and the related rat flea population.

Answer 408

Gimenez stain Direct microscopic examination for Rickettsia organisms is possible using such stains as Giemsa, Machiavello, or Gimenez. The recommended procedure is the nonspecific Gimenez stain, which colors the organisms a brilliant red against a green background.

Answer 409

Trench fever ROCHALIMEA/BARTONELLA QUINTANA: TRENCH FEVER Trench fever, caused by B. quintana, was largely considered a disease of the past. Clinical manifestations of trench fever range from a mild influenza-like headache and bone pain to splenomegaly (enlarged spleen) and a short-lived maculopapular rash.