Clinical Study Questions (Bacteriology) Flashcards
1
Q
What are the four different sterilizatioin methods commonly used in the lab, including their applications?
A
- moist heat - destroys at least the vegetative forms of bacteria; 2. dry heat - sterilizes inoculating loops and needles, and destroys discarded patient samples; 3. ionizing radiation - sterilizes disposable supplies; 4. disinfectants/chemical agents - destroys microorganisms via membrane damage, protein denaturation, and RNA/DNA damage
2
Q
What is the primary stain used in the Gram stain procedure?
A
crystal violet
3
Q
What is the mordant in a Gram stain?
A
Gram’s iodine
4
Q
What is the decolorizer in a Gram stain?
A
95% ethyl alcohol
5
Q
What is the counterstain in a Gram stain?
A
safranin
6
Q
At the end of the Gram staining procedure, what is the appearance of Gram positive and negative cells, respectively?
A
purple (+), red (=)
7
Q
What is the reason for the different staining properties of Gram+ and Gram= cells?
A
Gram= cells have more lipid in their cell walls than Gram+ cells do; this allows the decolorizing agent to penetrate the cell wall of Gram= cells more easily, which decolorizes them and in turn allows them to take up the counterstain
8
Q
How is a smear from solid media prepared for Gram stain?
A
bacterial specimen is picked up with a sterile inoculating loop and suspended in a drop of sterile water on a glass slide, which is then spread over a small area of the slide; this is allowed to air dry, and then the specimen is heat fixed by passing the slide quickly through a flame 2-3 times; the slide is then ready for staining
9
Q
What is the streak plate method for obtaining a pure culture?
A
An inoculum of organism is placed near the edge of an agar plate and streaked over the first quadrant with an inoculating loop. The second quadrant is then streaked with the same loop, passing into the first quadrant once or twice. Continue in this way through the third and fourth quadrants, but be sure NOT to pass back into the first quadrant when completing the fourth.
10
Q
What is the pour plate method and how is it used?
A
method of creating agar plates by inoculating melted agar in a serial dilution before pouring it into a series of Petri plates. It is used to estimate the number of organisms in water, milk, or food, and is generally used by public health labs.
11
Q
What is the significance of a colony count in urine?
A
urine is a normally sterile fluid, so the presence of bacteria not attributed to contamination is indicative of infection
12
Q
How is a colony count determined?
A
the number of organisms present are graded as few, moderate, or many on the basis of Gram stains and plate growth
13
Q
What is the significance of Gram stains in terms of colony counts?
A
differences in the amount of growth of different organisms may be related to their fastidiousness
14
Q
What is the process for culturing tissue samples sent from the operating room?
A
using aseptic technique, the tissue is finely minced with scissors into a mortar and pestle, or ground with a tissue grinder, with a small amount of water; the resulting liquid suspension is then placed on the appropriate media for routine, fungal, or AFB culture
15
Q
What visible signs are suggestive of growth in a blood culture bottle being read manually?
A
hemolysis; turbidity; gel-like appearance (due to coagulase or Staphylococcus); “stuff” floating on top (yeast or strict aerobe); gas bubbles (especially with Clostridium); color change (green may indicate S. pneumoniae, brown may be beta-Strep); colonies on top of RBCs
16
Q
What is done with blood cultures that are read manually and do not display any visible signs of growth?
A
automatically subculture after 24 and 48 hours, and then again before reporting out as negative; if the physician suspects fungi, bottles must be held for 4 weeks; Brucella, 3 weeks; tuberculosis, 8 weeks
17
Q
What might explain the frequent isolation of low grade or opportunistic pathogens from blood culture bottles?
A
contaminated samples
18
Q
When might sterility testing be done on blood for transfusion?
A
As per the WHO, all donated blood units are tested mandatorily for HIV, viral hepatitis, syphilis, and malaria. Once units are received, if any hemolysis, discoloration, or turbidity is seen, units are quarantined and tested before use.
19
Q
What is the appearance of alpha hemolysis on SBA?
A
partial hemolysis, often with green-appearing area arounf the colonies
20
Q
What is the appearance of beta hemolysis on SBA?
A
complete hemolysis, appearing as a clear zone around the colonies
21
Q
What is the appearance of alpha prime hemolysis on SBA?
A
small zone of alpha hemolysis surrounding the colony, with a wide zone of beta hemolysis extending into the media
22
Q
What is the appearance of gamma hemolysis on SBA?
A
no hemolysis
23
Q
What is wide-zone alpha hemolysis?
A
another name for alpha prime hemolysis
24
Q
Why is it clinically useful to group beta-hemolytic streptococci?
A
Group A causes severe, life-threatening illnesses such as pneumonia, septicemia, and meningitis; they are also the only kind resistant to bacitracin. While Group B can also cause septicemia and neonatal meningitis, they can sometimes be normal flora as well.
25
What important test method can confirm Group A beta-hemolytic streptococci?
bacitracin differentiation
26
What advantage does the pour plate method have over surface inoculation of SBA for detecting beta hemolysis?
two types of beta-hemolysins are released from this kind of streptococci - streptolysin S, and streptolysin O; the latter is destroyed by atmospheric oxygen and is therefore only demonstrable in deep colonies, which are more readily obtained using the pour plate method
27
How can S. pneumoniae be distinguished from alpha hemolytic streptococcus?
performing the optochin sensitivity, bile solubility, and/or an inulin fermentation test; S. pneumoniae is + for all, while alpha hemolytic streptococci are =
28
What test can be used in the lab to differentiate between streptococcus and staphylococcus?
catalase; strep is =, staph is +
29
What is coagulase?
enzyme produced by 97% of S. aureus; the exact chemical structure and mechanism are unknown, but the enzyme is known to clot human and rabbit plasma
30
What special safety precautions must be taken when culturing an organism suspected to be diptheria?
wear a lab coat and gloves while working with the specimen (or any specimen); conduct all procedures under a hood to avoid aerosols and splashes; limit the use of needles, syringes, and other sharp objects; decontaminate all wastes that contain or have come in contact with the organism via autoclave, chemical means, irradiation, or incineration
31
What cellular portion of S. pneumoniae is associated with virulence?
bacterial capsule
32
How would a cloudy spinal fluid be handled in the microbiology laboratory?
CSF is always considered STAT due to the instability of any cells and/or organisms contained in it; Gram stain should be performed immediately to provide the physician with a starting point for treatment, and also to determine the best media to culture the fluid with for confirmative identification of any organisms present
33
What is the proper collection and examination of sputum?
must be from a deep cough, uncontaminated with saliva or nasal secretions, and preferable an early morning specimen; if it cannot be cultured immediately, it should be refrigerated to prevent the overgrowth of normal flora
34
What is the best method for examining sputum?
culture
35
What is the significance of many squamous epithelial cells in a smear from a sputum sample?
squamous epithelial cells line the mouth, so this would suggest that the sample has been contaminated with saliva
36
With reference to the Enterobacteriaceae, what is the difference between the terms "coliform" and "enteric"?
coliforms are organisms considered to be part of the normal flora of the colon; enterics, or enteric pathogens, are the organisms considered to be intestinal pathogens
37
What two genera are the more common enterics isolated from diarrhetic stools?
Salmonella and Shigella
38
What tests are involved in the IMViC panel?
indole, methyl red, Voges-Proskauer, and citrate
39
What is ONPG and what is it used for?
o-nitrophenyl-B-D-galactopyranoside agar; organisms that lack permease that are grown on lactose-containing media can acquire permease, and the colony will exhibit delayed lactose fermentation - ONPG demonstrates this phenomenon. This agar is used primarily to differentiate between Salmonella (=) and Citrobacter (+)
40
What enzyme is produced by an indole + organism and how is it detected?
tryptophanase, which splits tryptophan into indole and alpha-aminoproprionic acid; presence can be demonstrated by adding Ehrlich's or Kovac's reagents (p-dimethylaminobenzaldehyde), which produces a red color soluble in ether, chloroform, and alcohol
41
What is the clinical significance of Pseudomonas aeruginosa?
may be considered normal flora in the URT or GI tract, though it is extremelt opportunistic and can "take over", especially in debilitated/immunocompromised patients; infections commonly occur at any site where moisture accumulates, especially the ear ("swimmer's ear") and weeping wounds; can cause severe to life-threatening infection, especially in the eyes (keratitis, corneal ulcer, opthalmitis); it is resistant to many antibiotics and disinfectants - intravenous treatment is required
42
How is TSI media interpreted when culturing enteric organisms?
A/A: tube is entirely yellow, organism ferments glucose and lactose, and/or sucrose; K/A - yellow butt with purple top, organism ferments glucose only, peptone is catabolized; K/K - tube is entirely purple, organism does not ferment sugars, peptone is catabolized
43
What are three general characteristics of the Clostridium genus?
anaerobic, capable of forming spores, typically large Gram+ rods
44
What is important to remember about Clostridium species when it comes to Gram staining?
some species will appear Gram variable, while some routinely stain Gram=; special potency antimicrobial discs should always be used to determine the true Gram reaction of a pink-staining anaerobic bacillus
45
What are the three major species of Clostridium and what diseases do they cause?
C. tetani (tetanus/"lock jaw"), C. botulinum (botulism), C. perfringens (gas gangrene)
46
What are the general characteristics of Haemophilus species?
tiny, pale-staining, pleomorphic Gram= rods; non-motile; aerobic or facultatively anaerobic; ferment carbohydrates; generally oxidase and catalast +; reduce nitrates to nitrites; obligate parasites on the mucus membranes of humans and animals
47
What are the growth factor requirements of Haemophilus species, and where are they found?
requires preformed factors in blood, designated X and V, which are found specifically in red cells; however, sheep red cells (used in most labs for blood agars) only contain X in the usable form (though chocolate agar contains X and V in usable forms); V can also be found in yeast and vegetable extracts, and can be produced by various microorganisms
48
What are the X and V growth factors?
hemin/hematin (X) and NAD-nicotinamide-adenine-dinucelotide (V)
49
What is the appearance of Haemophilus species on chocolate agar?
moist, wet-grey colonies with a "mousy" odor
50
What are the commonly encountered bacteria in spinal fluid, including their respective age groups?
Newborns - Group B streptococcus, E.coli, Listeria monocytogenes; Infants and Children - S. pneumoniae, N. meningitidis, H. influenzae type B; Adolescents and Young Adults - N. meningitidis, S. pneumoniae; Older Adults - S. pneumoniae, N. meningitidis, Listeria monocytogenes
51
How do endotoxins differ from exotoxins?
Endotoxins are part of the outer portion of the cell wall of Gram= bacteria and are released only when the cell dies. They are heat-stable, non-antigenic, and do not promote the formation of effective anti-toxins. Exotoxins are released while the cell is still alive. They form toxoids which can be used for vaccines; they are heat labile and antigenic; and usually associated with Gram+ organisms.
52
What would a positive smear for gonorrhea look like?
On blood agar - may be small and opaque (like Staph); may be wet and shiny, or dry and "heaped up"; or they may be white, grey, or yellow; colonies can be so membranous that they may "scoot" across the media in one piece; they may be alpha, gamma, or beta hemolytic (usually gamma). On chocolate agar (most common) - most colonies appear moist grey, possible cream-colored or yellow.
53
Why is it not a good idea to diagnose gonorrhea from a cervical or vaginal smear?
the vagina's normal flora can include saprophytic species of Neisseria; disease process is also different in females - it travels up to the fallopian tubes rather than to the outside of the body
54
What does PPLO stand for?
pleuropneumonia-like organisms
55
What is the clinical significance of PPLO?
term originally applied to Mycoplasma species; Mycoplasma pneumoniae is the causative agent of primary atypical pneumonia or Eaton's agent pneumonia ("walking pneumonia")
56
What is the causative agent of tuberculosis?
Mycobacterium tuberculosis
57
What is the process for concentrating a sputum for a tuberculosis culture?
N-acetyl-L-cysteine method is preferred for the concentration of all upper respiratory specimens; 4% NaOH is used as a decontaminating and digesting agent; N-acetyl-L-cysteine acts as a mycolytic agent which breaks up the specimen, allowing for enhanced recovery of the organism
58
What are the characteristics and pathogenic Mycobacteria species belonging to Runyon Group I?
photochromogens - produce a yellow pigment when exposed to light but have no pigment when grown in the dark; M. marinum, M. kansasii, M. simiae
59
What are the characteristics and pathogenic Mycobacteria species belonging to Runyon Group II?
scotochromogens - produce a yellow or orange pigment regardless of lighting conditions (many are slow growers); M. scrofulaceum, M. szulgai, M. xenopi
60
What are the characteristics and pathogenic Mycobacteria species belonging to Runyon Group III?
nonphotochromogens - organisms are nonchromogenic and nonphotoreactive, appearing as white to tan/buff colored; M. tuberculosis, M. bovis, M. avium-intracellulare (also known as M. avium complex or MAC), M. paratuberculosis
61
What are the characteristics and pathogenic Mycobacteria species belonging to Runyon Group IV?
rapid growers - produce visible colonies in less than 7 days (average 3-5 days), colonial morphology is variable: M. fortuitum, M. chelonei
62
What organisms cannot be tested for antibiotic susceptibility by the Kirby-Bauer disc diffusion method?
Gram= rods, Enterococcus, Staphylococcus, Streptococcus, Listeria, Bacillus, Corynebacterium, pathogenic Neisseria, and Haemophilus
63
Explain the Kirby-Bauer method for antimicrobial susceptibility testing.
A pure culture of the organism is inoculated into a suitable broth and incubated in air at 37*C for 2-4 hours. A lawn plate is prepared using a large Mueller-Hinton agar plate and allowed to set for a few minutes. Diffusion discs containing antibiotics are placed into the agar at evenly spaced intervals using aseptic technique. Plates are incubated at 37*C for 12-18 hours; following incubation, zones of inhibition are measured in mm and graded as sensitive (S), intermediate (I), or resistant (R).
64
What is differential media?
media that allows grouping of microorganisms on the basis of different characteristics displayed on the media; grows organisms in such a way that different forms can be distinguished due to additives to which different organisms have different responses
65
What is enriched media?
also called "supportive" media; media to which nutrients have been added to enhance the growth of fastidious organisms such as H. influenzae and N. gonorrhea
66
What is selective media?
media that will support the growth of one type of microorganism over another; may contain inhibitory substances to nonselective media
67
What is the purpose of modified Thayer-Martin (MTM) media and how does it work?
inhibits the growth of swarming Proteus through the addition of trimethoprim
68
What three organisms will grow readily on MTM agar?
N. gonorrhoea, N. meningitidis, N. lactamica
69
What is the concentration of sheep blood in an SBA plate?
5-10%
70
What is the concentration of sheep blood in Bordet-Gengou media?
15%
71
What are the five major components of most media and what does each component supply to the organisms?
peptone (partially digested protein that supplies nitrogen in a form usable by bacteria, also contains carbon); indicators (indicate pH changes due to carbohydrate metabolism, amino acid utilization, or urea breakdown); reducing agents (promote anaerobic conditions through the reduction of molecular oxygen to water); selective agents (substances that will inhibit or prevent the growth of certain microorganisms so that others may flourish); solidifying agents (growing organisms on solid media allows individual colonies to be isolated an indentified)
72
What specimens are cultured for the isolation of enteric pathogens?
most common specimen is stool, but they can also be isolated from sputum or wound cultures
73
Which enteric pathogen is the causative agent of bronchial pneumonia?
Klebsiella pneumoniae
74
What incubation environment should be used for enteric pathogens?
air or anaerobic (depending on specimen source), 37*C for 24-48 hours
75
How is MacConkey agar used for the culturing of enteric pathogens?
differential and selective media, used for primary plating and subculturing of enteric Gram= organisms
76
How is Levine's Eosin-Methylene Blue agar used for the culturing of enteric pathogens?
may be used in preference to MacConkey for the detection of enteric bacilli
77
How is Deoxycholate Citrate agar (DCA) used for the culturing of enteric pathogens?
differential media designed for the isolation of Gram= bacilli
78
How is Bismuth Sulfite agar used for the culturing of enteric pathogens?
highly selective for the isolation of Salmonella from feces and other pathologic material
79
How is Salmonella-Shigella (SS) agar used for the culturing of enteric pathogens?
used for the isolation of Salmonella and Shigella
80
How is Selenite-F broth used for the culturing of enteric pathogens?
enrichment media for Salmonella and some Shigella (isolation success is greater with Salmonella)
81
How is Hajna's Gram-Negative (GN) broth used for the culturing of enteric pathogens?
selective enrichment media devised for the cultivation of Salmonella and Shigella (coliforms are inhibited only up to 6 hours)
82
How is Xylose-Lysine-Deoxycholate (XLD) agar used for the culturing of enteric pathogens?
selective and differential media recommended for the isolation of enteric pathogens, especially Shigella
83
How is Hektoen Enteric (HE) agar used for the culturing of enteric pathogens?
isolates and differentiates Salmonella and Shigella from the normal enteric flora
84
What are enterococci and why is their identification clinically important?
group of streptococci originally named for its usual habitat in the enteric tract; frequently cause urinary tract infections, wound infections, and sub-acute bacterial endocarditis (SBE)
85
Describe a quick, 24-hour, reliable scheme to differentiate the enterococci from all other streptococci.
Enterococci can grow in the presence of 40% bile, and they can hydrolyze esculin. Streak a slant of bile-esculin agar with a suspected colony and incubate at 37*C for 18-24 hours. Growth accompanied by a jet-blackening of the media is + and suggests enterococci.
86
What organisms are cultured for primarily with a nasopharyngeal (NP) specimen?
Bordetella pertussis, N. meningitidis, S. aureus/MRSA
87
Why should a throat culture be placed on sheep blood as opposed to human blood?
human blood may be contaminated with antibiotics, antibodies, or anticoagulants
88
What is the purpose of stabbing the agar when inoculating a throat culture?
streptolysin O is demonstrable only in deep colonies as it is destroyed by atmospheric oxygen; it is produced by beta hemolytic streptococci, and its presence indicates a recent/current strep infection, especially if accompanied by a positive ASO titer
89
Which anaerobe produces a black pigment that fluoresces under UV illumination, and what is its significance?
Prevotella melaninogenicus; normal flora in the URT, GU tract, and especially in the vagina; opportunist in wounds, abscesses, etc., especially in mixed infections with aerobes; species is also resistant to kanamycin and vancomycin
90
What may suggest anaerobic infection?
specimen source is a deep wound, abscess, tissue/biopsy, trans-tracheal aspirate, blood, body fluid from normally sterile areas, suprapubic aspirate (urine), or aseptically collected uterine specimens
91
What five organisms can cause food poisoning?
Campylobacter jejuni, Salmonella, Shigella, E. coli, and Listeria
92
Does an organism need to be present in the victim for symptoms of food poisoning to be evident?
no; food poisoning is due to an exotoxin, which can be released while the organism is still alive - therefore, the organism does not have to ever be ingested to cause illness
93
How does food infection differ from food poisoning?
food infection is the result of an endotoxin, which means the organism can only release it upon death; viable organisms must be ingested to cause illness
94
What is the difference between bacteremia and true sepsis?
bacteremia is the presence of bacteria in the blood, but it is not always serious - it can occur after meals, following tooth extraction, and after prophylaxis; sepsis (septicemia) is when bacteria in the blood are multiplying and/or producing toxins in the blood, which travel to tissues and cause disease - this is a life-threatening situation
95
How can sepsis be confirmed in the laboratory?
read blood culture bottles for signs of bacterial growth (hemolysis, turbidity, coagulation, "stuff" floating on top, gas bubbles, etc.); if these signs are seen, subculture after 24-48 hours and identify the organism
96
If a patient is thought to have whopping cough, what specimen would be recommended and how would it be processed in the lab?
Bordetella pertussis is fastidious and requires media containing blood-potato-glycerol. Bordet-Gengou is a good media for this organism, on which it will appear as small, smooth colonies with a pearl-like luster after incubating at 35-37*C for 3-5 days. This media, however, does not inhibit the growth of normal flora, so any suspicious colonies need to be Gram-stained, looking for Gram= coccobaccili morphology. Specimen should be bedside cough plate.
97
What other medium can be used to culture suspected B. pertussis that does not require Gram staining to confirm?
Regan-Lowe media; it is a charcoal agar supplemented with 10% horse blood and 40mg/dL cephalexin, which does inhibit normal flora. Specimen should be a nasopharyngeal swab collected with a calcium alginate or polyester-tipped swab and transported to the lab in Regan-Lowe transport media. Incubation requirements are the same as with Bordet-Gengou.
98
What biochemical characteristics would identify a culture as B. pertussis?
oxidase =, non-motile, citrate/indole/urea =, non-utilizer
99
Because B. pertussis cultures are only 60-70% sensitive for biochemical characteristics, what is considered the best method for identity confirmation?
direct fluorescent antibody techniques, ELISA, or DNA testing
100
What is the only acceptable respiratory specimen for anaerobic culture and why?
trans-tracheal aspirate; most anaerobes are endogenous (normal flora), and any other specimen type would make it impossible to rule this out
101
A gram-stained smear from a cerebrofacial nodule reveals Gram+, branching, filamentous rods. What diagnosis would this suggest and what culture procedures should be followed?
Actinomycosis ("lumpy jaw"), caused by Actinomyces. Lesions caused by this will contain yellowish-white granules. This organism is a strict anaerobe, so the granules should be collected in and washed several times with sterile NaCl. Granules should then be aseptically crushed and placed in thioglycolate broth; if growth in the broth is observed, subculture to anaerobic SBA. Biochemical separation is determined by carbohydrate fermentation, indole production, esculin hydrolysis, and gelatin hydrolysis. All species for acetic, succinic, and lactic acid.
102
Why should all respiratory specimens be incubated in a CO2 environment?
non-Group A beta-hemolytic streptococci are isolated significantly more often when incubated in this environment
103
What does MIC stand for and what is its clinical use?
Minimum Inhibitory Concentration; the smallest concentration of a particular drug that will completely inhibit an organism
104
What is the Neufeld-Quellung reaction and to which organisms may it be applied?
a capsular swelling reaction used to demonstrate the presence of capsules on bacteria - when organisms are brought into contact with homologous anticapsular serum, they are seen to be surrounded by a sharply demarcated halo (stained with methylene blue); used on pneumococci
105
What variables might influence the zone size on a Kirby-Bauer susceptibility test?
resistance of the organism being tested; diffusion properties of the agar and antibiotic discs; pH of the media (should be 7.2-7.4); thickness of the agar (80-90mL/plate); agar having been stored in the refrigerator for more than a week; plates containing excessive condensation
106
What is the purpose of boiling a bacterial suspension when performing slide agglutination tests?
removes the capsular antigen
107
What is beta-lactamase and how is it related to bacteriology?
an enzyme produced by some bacteria that disrupts the four-membered beta-lactam ring of certain antibiotics; bacterial strains possessing this enzyme are resistant to penicillin and ampicillin
108
What is toxic shock syndrome?
multi-systemic illness characterized by a clinical syndrome that includes fever, hypotension, orthostatic dizziness, erythroderma, and varying degrees of vomiting, diarrhea, renal failure, headache, chills, sore throat, and in severe cases, death
109
What is the causative agent of toxic shock syndrome?
toxic shock syndrome toxin (TSST-1); although first observed in females and associated with improper use of hyperabsorbent tampons, it has also been observed in patients of both sexes as a complication of staphylococcal abscesses, osteomyelitis, post-surgical wounds, infections, and post-influenza pneumonia
110
If Vibrio cholera is suspected, what types of media should be employed?
stools should be transported in closed containers to preserve moisture and transferred to thiosulfate-citrate-bile-sucrose (TCBS) agar as soon as possible; if cultures cannot be set up immediately, organisms will remain viable in Cary-Blair semisolid transport media for an extended period; to enhance isolation, specimens can also be inoculated into alkaline peptone water (APW) enrichment broth, which will inhibit normal intestinal flora for 12-18 hours and allows multiplication of Vibrio organisms
111
What is one major unusual characteristic of Vibrio cholera?
it is halophilic (salt-loving)
112
A patient presents with a severe case of gastroenteritis 24 hours after ingesting large quantities of raw clams. What would be the main organism to consider and what special biochemical test can be used to confirm it?
Salmonella; suspected organism should be antigen types using a suspension of the organism in 0.85% saline; if the Vi antigen "comes down", heat the suspension to remove the K antigen and retype. If necessary, the H antigen can be sent to the state lab.
113
What is another name for optochin, and how is it used in the laboratory?
ethylhydrocuperene hydrochloride; differentiates S. pneumoniae from other alpha-hemolytic streptococci, as it is the only one susceptible to it
114
What biochemical test is used to separate the genera Morganella, Providencia, and Proteus from the rest of the Enterobacteriaceae?
all three are phenylalanine +
115
How can Morganella, Providencia, and Proteus be separated from one another?
Proteus exhibits swarming motility and produces H2S, while Morganella has neither of these traits; Providencia is urea = and Morganella is urea +
116
What two species of Corynebacterium elicit a diptheria toxin and how can they be differentiated?
C. diptheriae (urea and gelatin =) and C. ulcerans (urea and gelatin +)
117
How can Corynebacterium, Listeria, and Erysipelothrix be differentiated through biochemical means?
catalase (Erysipelothrix =, others +); sugar fermentation - Corynebacterium (glucose and maltose), Listeria (glucose and lactose), Erysipelothrix (glucose and lactose, H2S on TSI); motility (Listeria the only motile genus, more so at 25*C, showing "umbrella" shape)
118
What was the former name of Morganella morganii, and why was its name changed?
Proteus morganii; it does not exhibit swarming motility or produce H2S, and DNA homologies have now shown that it is only related to Proteus by 20%
119
A premature child is thought to have meningitis. What two organisms would be most seriously considered?
Group B Streptococcus, Listeria monocytogenes
120
What are two commonly isolated anaerobes?
Bacteroides fragilis, Prevotella-Porphyromonas group
121
What is the morphology of Bacteroides fragilis, and what are some identifying characteristics?
non-motile Gram= rods with rounded ends; tend to be pleomorphic, often with vacuoles; may be encapsulated; growth enhanced by bile; resistant to karamycin and penicillin, but sensitive to rifampin; grow well on KV agar; most are catalase +
122
What is the morphology of Prevotella-Porphyromonas group, and what are some identifying characteristics?
pale-staining Gram= coccobacilli; some may be pleomorphic; colonies are generally pigmented and may fluoresce brick-red under UV light; all are bile sensitive; Prevotella produces acetic, succinic, and lesser amounts of isobutyric, isovaleric, and lactic acids; Porphyromonas produces acetic, succinic, and butyric acid with lesser amounts of propionic, isobutyric, and isovaleric acids.
123
What is gas-liquid chromatography (GLC) and how can it be used in the laboratory?
method of gas chromatography in which the substances to be separated are moved by an inert gas along a tube filled with a finely divided inert solid coated with a non-volatile oil; each component migrates at a rate determined by its solubility in oil and its vapor pressure; technique can be used to identify anaerobes - for example, identifying type and quantity of acid produced by organisms such as Prevotella
124
What is the clinical importance of Nocardia species?
found worldwide in soil and on plant material; infection can occur via pulmonary or cutaneous routes and is very serious (approximately 40% of diagnoses are made at autopsy); mortality rate is high, and those that survive often suffer significant tissue damage
125
What is the clinical importance of Streptomyces species?
infrequent pathogens, though they can cause mycetoma infections; also the largest antibiotic-producing genus, producing antibacterial, antifungal, and antiparasitic drugs, as well as a wide range of other bioactive compounds, such as immunosuppressants
126
How do the growth characteristics and identification of Nocardia and Streptomyces species differ from other bacteria?
Gram stains show delicate, branching filaments that resemble the hyphae of fungi; colonial formation resembles that of fungi; and they can cause subcutaneous, lymphocutaneous, and respiratory infections similar to those caused by fungi
127
What is the difference between enrichment media and enriched media?
enrichment media are broths designed to encourage the growth of small numbers of a particular organism while suppressing the normal flora; enriched media, by contrast, does not suppress normal flora
128
What is a prime example of the use of enrichment media?
GN broth and SF broth are used to enhance the growth of intestinal pathogens; there is so much normal flora present in the intestines that any pathogens present may be overgrown on regular media
129
What are two methods that can be used to detect beta-lactamase positive (ampicillin resistant) H. influenzae?
Any Gram= coccobacilli should be cultured onto Mueller-Hinton agar with X and V factor strips, as H. influenzae requires both for growth; can also be identified through "satellite phenomenon" - SBA plate is streaked as for isolation, and a streak of S. aureus is placed across the first two quadrants; S. aureus produces the V factor lacking in SBA, and H. influenzae will grow as tiny colonies around the streak
130
What is the principle of Kliger's Iron Agar (KIA)?
used to characterize Gram= bacilli by testing for acid and gas production from glucose and lactose metabolism
131
How is KIA interpreted?
lactose fermenters appear as A/A (yellow/yellow); non-lactose fermenters appear K/A (purple/yellow); H2S production causes a black color change; bubbles indicate gas
132
What reagent is present in KIA?
phenol red (pH indicator)
133
What is the principle of Lysine-Iron Agar (LIA)?
determines if a bacterial species decarboxylates or deaminates lysine, and detects H2S production
134
How is LIA interpreted?
purple color change indicates lysine decarboxylation; purple/yellow indicates lysine is not utilized; plum or reddish-purple/yellow indicates lysine deamination; blackening indicates H2S production
135
What reagent is present in LIA?
ferric ammonium citrate
136
What is the principle of Simmons Citrate Agar (SCA)?
determines whether Gram= bacilli can utilize citrate as a carbon source
137
How is SCA interpreted?
growth on the slant with or without royal blue color change is +; no growth and no color change is =
138
What reagent is present in SCA?
bromthymol blue
139
What is the principle of the urease test?
detects organisms that produce the enzyme urease
140
How is the urease test interpreted?
urease production raises the pH of the media and causes a bright pink color change
141
What reagent is used for the urea test?
phenol red
142
What does the SIM test battery include?
detects sulfide production, indole, and motility
143
How is the SIM battery interpreted?
sulfide produces a black coloring; indole produces a pink to red color after the addition of the reagent; cloudiness of media indicates motility
144
What reagent is used in the SIM battery to indicate indole production?
Kovac's reagent (p-dimethylaminobenzaldehyde)
145
What does the MIO test battery include?
motility, indole, and ornithine utilization
146
How is the MIO battery interpreted?
purple is +; yellow is = (indicates glucose was utilized instead)
147
What reagent is used in the MIO battery?
Kovac's reagent
148
What is the principle of the Phenylalanine Deaminase (PAD) test?
illustrates the ability of Morganella, Proteus, and Providencia to break down phenylalanine
149
How is the PAD test interpreted?
green color indicates a + reaction
150
What is the reagent used in the PAD test?
10% ferric chloride; the green color is produced by ferric ions reacting with phenylpyruvic acid, the end result of phenylalanine breakdown
151
What is the principle of Moeller decarboxylase broth?
detects the presence of decarboxylases and dehydrolases that break down specific amino acids
152
How are Moeller decarboxylase reactions interpreted?
yellow color is acidic (=), purple color is alkaline (+)
153
What is the principle of the CTA sugars test?
medium that supports most fastidious organisms, though mainly used to study the fermentation reactions of Neisseria
154
How is the CTA sugar test interpreted?
in plate format, carbohydrate discs are added to the agar surface, and any yellow coloring around them represents fermentation of their respective sugar; in tube format, tubes already containing the individual sugars are stabbed with organism, and yellow color change indicates a + reaction
155
What reagent is used for the CTA sugars test?
phenol red (pH indicator)
156
What is the principle of the O-F sugars test?
distinguishes oxidative acidity from fermentive; contains one tube each of dextrose, lactose, and sucrose
157
How is the O-F sugars test interpreted?
oxidation - open tube is yellow, petrolatum tube is green; fermentation - both tubes are yellow
158
What reagent is used for the O-F sugars test?
bromthymol blue (acid indicator)
159
What is the principle of KCN broth?
encourages the growth of Klebsiella, Citrobacter, and Proteus; presence of cyanide in the agar inhibits E. coli, Salmonella, and Shigella
160
How is KCN broth interpreted?
cloudy growth at any time up to 48 hours after inoculation is considered +; minimal/no growth is considered =
161
What is the principle of Mannitol Salt Agar (MSA)?
selective media for the isolation of pathogenic (coagulase +) staphylococci from contaminated sources such as feces
162
How is MSA interpreted?
after 36 hours incubation at 35*C under increased CO2 tension, pathogenic colonies will be yellow and surrounded by yellow zones; non-pathogens will be small, white, and surrounded by red or purple zones
163
What reagent is present in MSA?
phenol red (pH indicator)
164
What is the principle of the NF screen?
used to identify pigmented strains of P. aeruginosa and P. fluorescens/putida group
165
In the NF screen, what does the GNF tube test for and how is it interpreted?
glucose fermentation and N2 gas production; fluorescent slant with yellow/green growth is +, yellow butt is glucose +, cracks and/or bubbles is N2 +; white growth, red/orange butt, medium intact - all = results
166
In the NF screen, what does the 42*P tube test for and how is it interpreted?
growth tolerance at 42*C; green slant - pyocyanin +; growth on slant - 42*C tolerance; white/no growth is =
167
What reagents are present in the NF tests?
pH indicator
168
What is the principle of sodium hippurate broth?
Group B streptococcus can be differentiated from most other beta-hemolytic streptococcus by the production of hippurase
169
How is sodium hippurate broth interpreted?
heavy white precipitate remaining longer than 10 minutes is +; no precipitate after 10 minutes is =
170
What reagent is used in sodium hippurate broth?
FeCl3 * 6H2O, 2% aqueous HCl
171
What is the principle of the Novobiocin test?
distinguishes S. saprophyticus from other coagulase = staphylococcus using Novobiocin discs
172
How is the Novobiocin test interpreted?
zone of inhibition >16mm, or tube turbidity less than that in the control tube indicates sensitivity
173
What is the principle of the gelatin liquefaction test?
certain bacterial genera are able to break down gelatin
174
How is the gelatin liquefaction test interpreted?
solid stabs of nutrient gelatin are incubated overnight, then refrigerated for 10 minutes; liquid medium indicates + results; if medium stays solid, result is =
175
What is the principle of egg yolk agar?
enriched, non-selective, differential medium used to detect lecithinase and lipase production and proteolytic activity in the presumptive ID of various Clostridium, Fusobacterium, and Prevotella species
176
How is egg yolk agar interpreted?
opaque zone of white precipitin (lecithinase +); iridescent sheen (lipase +); clear zones around colonies (proteolysis +)
177
What is the principle of the phenol red sugar test?
differentiates Gram= enteric bacteria based on sugar fermentation
178
How is the phenol red sugar test interpreted?
yellow (fermentation +), fuschia (fermentation =, peptone utilization +); bubbles in Dunham tube (gas +)
179
What reagent is used in the phenol red sugar test?
phenol red
180
What is the principle of DNase media?
detects the production of DNase by pathogenic strains of Staphylococcus
181
How is DNase media interpreted?
after overnight incubation, medium under and around inoculum turning pink/rose is +
182
What reagent is present in DNase media?
0.005% toluidine blue
183
What is the principle of the methyl red test?
broth used is a delicately buffered glucose medium in which Gram= bacilli produce a high degree of acidity
184
How is the methyl red test interpreted?
red color + (acidic), yellow color = (alkaline)
185
What reagent is used for the methyl red test?
methyl red
186
What is the principle of the Voges-Proskauer (VP) test?
some bacteria have the ability to produce acetylmethyl carbinol (acetoin) from glucose; at an alkaline pH, acetoin is oxidized to diacetyl, which reacts with the guanidine compound in the buffered deoxycholate glucose broth
187
How is the VP test interpreted?
pink to red color appearing within 5 minutes of reagent addition is +
188
What reagents are used in the VP test?
alpha-napthol (5% in 95% ethyl alcohol) and KOH (40% in distilled water)
189
What is the principle of the nitrate reduction test?
the reduction of nitrate leads to the formation of nitrite and may progress to the liberation of nitrogen
190
How is the first part of the nitrate reduction test interpreted?
observation of a gas bubble in the Dunham tube is +; if no gas is observed, add reagent - red color is +, no color is = (proceed to second part of test)
191
How is the second part of the nitrate reduction test interpreted?
add reagent - red color is NO2 =; no color change indicates possible further reduction to nitrogen
192
What reagents are used in the nitrate reduction test?
part one - sulfanilic acid, alpha-napthylamine; part two - zinc dust
193
How is the Taxo-A test performed and interpreted?
Type of differentiation disc containing bacitracin, used for sensitivity testing to distinguish Group A streptococcus from Group D. On SBA, streak and stab one quadrant with a beta-hemolytic colony; repeat with 2-3 more colonies. Place a disc in the center of each streaked quadrant and incubate the plate overnight at 35*C. Any zone of inhibition of beta-hemolytic growth around the disc indicates bacitracin sensitivity, indicative of Group A.
194
How is the Taxo-P test performed and interpreted?
Type of differentiation disc containing optochin, used for sensitivity testing to distinguish S. pneumoniae from other alpha-hemolytic streptococci. Test is performed the same way the Taxo-A test is performed. If 6mm discs are used, zone of inhibition >/= 14mm indicates S. pneumoniae; with 10mm discs, zone should be >/= 16mm.
195
How is the PYR test performed and interpreted?
PYR disc is moistened with a drop of demineralized water. "Paste" from suspected colony (from 18-24 hr. pure culture) is rubbed onto the disc with a sterile loop or wooden applicator stick. Incubate at room temperature for 2 minutes. One drop of PYR reagent is added, and up to 1 minute is allowed for color change. Pink or red color is +, yellow or no color is =. Positive results indicate Enterococcus or Group A Streptococcus.
196
How is the X/V/XV factor strip test performed and interpreted?
suspected Haemophilus colonies are streaked over a Mueller-Hinton plate. X, V, and XV factor strips are placed in three quadrants (4th is a control), and the plate is incubated at 37*C under CO2. Growth around strips indicates which factors the colony needs, thereby identifying the species.
197
How is the CAMP test performed and interpreted?
S. aureus is streaked down the center of an SBA plate. Towards the bottom, streak the suspect culture perpendicular to the S. aureus streak on both sides. At the top, repeat this step with Group A and Group B controls, one on one side and one on the other. Incubate aerobically at 35*C for 18-24 hours. An arrowhead-shaped area of increased hemolysis adjacent to the S. aureus indicates production of the CAMP factor. A bacitracin test should also be performed on the same plate - organisms that are CAMP + and bacitracin = are presumptive Group B streptococcus; CAMP + bacitracin + could be A or B and requires serological testing; CAMP and bacitracin = means that the organism is neither Group A or B.
198
How is the oxidase test performed and interpreted?
2-3 drops of reagent are placed on the center of a piece of Whatman No. 1 filter paper inside a Petri dish. Test colony is then rubbed into the reagent spot with a loop. Dark purple color change in 5-10 seconds indicates the organism is oxidase +.
199
What is the reagent used for the oxidase test?
1% solution of tetramethyl-p-phenylenediamine hydrochloride
200
How is the toxigenicity test for diptheria performed and interpreted?
Known as the Elek test (in vitro); controls and unknowns are streaked on media of low iron content in single straight lines parallel to each other and 10 mm apart. A filter paper strip impregnated with diptheria antitoxin is laid along the center of the plate perpendicular to the streaks. The plate is incubated at 35*C and examined at 18, 24, and 48 hour intervals. A toxin-producing strain will show a white precipitin line about 4-5 mm from the filter paper; if two + strains are streaked next to each other, the precipitin lines of each one will join to form the "arch of identity".
201
How is the niacin test performed and interpreted?
Reagent-impregnated strips will turn from colorless to yellow when in the presence of M. tuberculosis, which produces nicotinic acid (free niacin) instead of converting niacin to niacin ribonucelotide like most Mycobacteria do.
202
How is the catalase test performed and interpreted in the case of Mycobacteria?
Using an 18-24 hour agar slant culture, or a 24-48 hour broth or thioglycolate culture, add 1 mL of 3% hydrogen peroxide. Rapid ebullition of gas indicates a + result in most cases; however, in the case of Mycobacteria, the test is only considered + if it remains so after being heated to 68*C for 20 minutes.
203
How does the nitrate test for AFB organisms differ from that of non-AFB organisms?
test is performed similarly, but the substrate is slightly different, and the test is quantitative (negative to 5+) rather than qualitative
204
What is the Tween 80 hydrolysis test for AFB organisms, and how is it interpreted?
Tween 80 is the trade name of a detergent that is used to identify Mycobacteria that have a lipase capable of splitting the reagent into oleic acid and polyoxyethylated sorbitol. The products of the reaction will alter the optical rotation of transmitted light which causes a pink color change. This test is + for M. kansasii (in 3-6 hours), and can also distinguish M. gordonae (+) from M. scrofulaceum (=).
205
What special procedures and/or conditions are required to culture Corynebacterium diptheriae?
requires selective media, such as Loeffler's serum agar, Pai's egg medium, or potassium tellurite (Tinsdale) medium
206
What special procedures and/or conditions are required to culture Listeria monocytogenes?
will grow on selective media (such as McBride's agar), appearing as blue-green colonies that resemble water droplets; also capable of growth at anywhere from 0-45*C (demonstrated through cold enrichment technique)
207
What special procedures and/or conditions are required to culture Brucella species?
Fail to grow on routine Gram = agar, although they can be grown on SBA. Blood cultures should be grown in Casteneda bottles - these contain TSB/Brucella broth and a slant of TSA. They're incubated on their sides to encourage the growth of colonies on the slant.
208
What special procedures and/or conditions are required to culture Francisella species?
requires cystine, blood, and dextrose (Francis media), but can also grow on chocolate agar or CYE; because it is so dangerous to work with, reference labs usually make the identification
209
What special procedures and/or conditions are required to culture Leptospira species?
requires special media (Fletcher's media) that contains rabbit albumin, amino acids, and various salts
210
What special procedures and/or conditions are required to culture Haemophilus ducreyii?
requires only the X factor, but does not grow well on laboratory media; grows best in clotted rabbit blood
211
What special procedures and/or conditions are required to culture Cryptococcus neoformans?
CSF should be uncentrifuged; will grow best on BHI incubated at 37*C, though it will grow at room temperature on most fungal media (excepting mycosel, as cyclohexamide inhibits it)
212
What special procedures and/or conditions are required to culture Mycobacterium tuberculosis?
although it is aerobic, growth is enhanced by CO2 on primary isolation; best media is either Lowenstein-Jensen (LJ) or Middlebrook
213
What special procedures and/or conditions are required to culture Neisseria gonorrhoeae?
will grow on chocolate agar, but modified Thayer-Martin is the best option; requires 35*C (no higher than 37-38*C), adequate but not excessive moisture, and 5-10% CO2; specimens must be transported in Trans-grow media
214
What special procedures and/or conditions are required to culture Yersinia pestis?
can be grown on MacConkey agar at 25*C, or on special selective media known as Yersinia CIN (cefsolodin irgasan novobiocin); cold enrichment technique can also be used on this organism
215
Which Enterococcus species is associated with urinary tract and wound infections?
E. faecalis
216
What conditions are Peptostreptococcus species associated with?
abscesses and wound infections
217
Which species of Staphylococcus is associated with boils, carbuncles, and osteomyelitis?
S. aureus
218
Which species of Streptococcus is associated with neonatal meningitis and sepsis?
S. agalactiae
219
Which species of Streptococcus is associated with pharyngitis and rheumatic fever?
S. pyogenes
220
What is Escherichia coli known to cause other than food poisoning?
urinary tract infections
221
What is the causative agent of bronchial pneumonia?
Klebsiella pneumoniae
222
What condition does Salmonella enteritidis cause?
gastroenteritis
223
What is the causative agent of bubonic plague?
Yersinia pestis
224
Which species of Yersinia is associated with mesenteric lymphadenitis?
Y. pseudotuberculosis
225
What are the oxidase and motility reactions of the Acinetobacter species?
oxidase =, non-motile
226
Which Aeromonas species can cause acute diarrhea when acquired through contaminated soil or H2O?
A. hydrophila
227
Which Campylobacter species would cause gastroenteritis through contaminated milk or poultry?
C. jejuni
228
Which Flavobacterium species is associated with neonatal meningitis?
F. meningosepticum
229
Which organism is a highly resistant opportunist in wounds and burns, and causes the condition known as "swimmer's ear"?
Pseudomonas aeruginosa
230
What are the oxidase and motility reactions of Stenotrophomonas maltophilia?
oxidase =, motile
231
Which Vibrio species would cause gastroenteritis through contaminated seafood?
V. parahemolyticus
232
What is Bacillus cereus associated with?
food poisoning from contaminated fried rice
233
What is the causative agent of Lyme's disease?
Borrelia burgdorferi
234
What is the causative agent of non-gonococcal urethritis (NGU)?
Chlamydia trachomatis
235
What is the causative agent of diptheria?
Corynebacterium diptheriae
236
What is the causative agent of conjunctivitism ("pink eye")?
Haemophilus aegypticus
237
Which species of Listeria is known to cause neonatal meningitis?
L. monocytogenes
238
Which Pasteurella species can cause infection following a cat or dog bite?
P. multocida
239
What is the genus of the species "acnes", associated with skin infections?
Propionibacterium
240
Compare and contrast sterilization and disinfection.
Both methods are used for the same purposes - to prevent the spread of infection, to prevent sample contamination, and to prevent the spoilage and decomposition of food. However, sterilization will completely kill or remove organisms, while disinfection merely inhibits their growth and reproduction without necessarily killing them.
241
Define bacteriostatic.
chemical or other means of inhibiting the growth or reproduction of bacteria
242
Define bacteriocidal.
substance that kills or is capable of killing bacteria
243
Define spores.
in bacteria - the protective, dehydrated, dormant state of some microorganisms that is resistant to drying, heat, chemical disinfectants, and radiation; in fungi - the microscopic biological particles that allow reproduction
244
Define thermophilic.
characteristic of some bacteria indicating their optimum growth temperature as 50-60*C, although they will tolerate much higher ranges
245
Define infection.
pathogen is able to overcome the natural defenses of the host and grow in the body of the host; obligate pathogens are always able to do this, while secondary/opportunistic pathogens may require help
246
Define colonization.
the formation of compact population groups of the same microorganism; the development of a bacterial infection on or in an individual
247
Define halophilic.
organisms requiring a salt-rich environment for their growth and survival
248
Define nosocomial.
originating or taking place in the hospital, especially in reference to infection
249
Define carrier.
individual that harbors a pathogenic organism but has no signs or symptoms of the disease, and is capable of passing it on to someone else
250
Define pyocyanin.
toxic blue crystalline pigment (C13H10N2O) that is formed in the metabolism of P. aeruginosa
251
Define pleomorphic.
the ability of some bacteria to alter their shape or size in response to the environmental conditions
252
Define resistant.
microbes that are less treatable with one or more medications normally used to do so
253
Define colicins.
a type of bacteriocin (proteinaceous toxins produced by bacteria to inhibit the growth of similar/closely related bacterial strains) produced by and toxic to some strains of E. coli
254
Define mordant.
substance, usually a salt of metal, used to give dyes an attachment point in the microbiological staining process
255
Define pathogen.
organism that causes disease; obligate pathogens will always cause disease, while opportunistic pathogens cause disease only under certain circumstances
256
Define diptheroid.
one of a group of local infections suggesting diptheria, but caused by microorganisms other than C. diptheriae; any microorganism resembling diptheria
257
Define geophilic.
soil-originating fungal species; any microorganism indigenous to soil
258
What is the use of Colistin-Naladixic Acid (CNA)?
selective medium for Gram+ organisms such as Staph and Strep, particularly useful for isolating them from material with mixed flora; permits the demonstration of hemolysis for Strep and coagulase testing of Staph.
259
What is the use of Phenylethyl Alcohol (PEA)?
suppresses the growth of Gram= organisms, allowing identification of Gram+ cocci, such as Staph and Strep, in autopsy materials and feces
260
What is the use of thioglycollate and how is it interpreted?
Very useful in the primary isolation of both aerobes and anaerobes; Reazurin acts as an indicator of oxidation-reduction potential. At the interface of media and atmosphere, media will be oxidized, resulting in a pink-colored ring; aerobes will grow in and around this ring, while anaerobes will grow further down.
261
What is the use of Levine's Eosin-Methylene Blue (EMB) and how is it interpreted?
Some labs use this instead of MacConkey for the detection of enteric bacilli; it can also be used for the isolation of Candida albicans. Lactose-fermenting organisms produce acid which reacts with the eosin and methylene blue, giving the colonies a blue-black center. Non-lactose fermenting colonies will appear colorless.
262
What is the use of MacConkey agar and how is it interpreted?
Differential and selective media used for primary plating and subculturing of enteric, Gram= organisms. Bile salts and crystal violet inhibit the growth of Gram+ organisms. Lactose fermenters (coliforms) will produce red colonies while non-fermenters will produce colorless colonies.
263
What is the use of Salmonella-Shigella (SS) media and how is it interpreted?
Used primarily for the isolation of Salmonella and Shigella. Inhibits Gram+ organisms with bile salts and crystal violet, and inhibits coliforms with brilliant green. Lactose fermenters appear red while non-fermenters are colorless. Hydrogen sulfide producers will have colonies with black centers.
264
What is the use of Hektoen Enteric (HE) agar and how is it interpreted?
Isolates and differentiates Salmonella and Shigella from normal enteric flora. H2S production yields a black precipitate and/or colonies. Lactose fermenters are yellow or orange; non-fermenters are blue-green.
265
What is the use of Xylose-Lysine-Deoxycholate (XLD) media and how is it interpreted?
Selective and differential media recommended for the isolation of enteric pathogens, especially Shigella. Salmonella and Shigella both appear as red colonies, but Salmonella will have black centers. Lysine = fermenters appear yellow, such as E. coli, Citrobacter, and Proteus.
266
What is the use of Mueller-Hinton agar and what does it consist of?
Medium devised for the primary isolation of N. gonorrhoeae and N. meningitidis. Can also be used for determination of antibiotic sensitivity, particularly with the Kirby-Bauer technique. Medium essentially consists of a beef infusion with peptone, starch, and agar.
267
What is the use and interpretation of Thiosulfate-Citrate-Bilesalt-Sucrose (TCBS) agar?
Used for selective isolation of Vibrio. V. cholerae produces yellow colonies in 18-24 hours; non-pathogenic Vibrio form colonies with blue to greenish centers. Proteus and Enterococcus may produce small translucent colonies (excepting P. mirabilis, which ferments sucrose and would appear yellow). Pseudomonas and Aeromonas appear blue.
268
What is the use of Sabouraud's agar and what does it contain?
also called SDA or Sabs; best general all-purpose medium for the primary isolation of fungi, because just about any fungus will grow on it; contains peptone and dextrose, and is good to use for the maintenance of fungal cultures
269
What is the use of Mycosel and what does it consist of?
Sabs with chloramphenicol (inhibits most bacteria) and cyclohexamide (inhibits saprophytic fungi); can be used for the primary isolation of fungal cultures and is particularly useful in the isolation of ringworm.
270
What is the use of Middlebrook 7H-10 and what does it consist of?
serum albumin agar medium containing defined salts, vitamins, cofactors, glycerol, malachite green, and enrichments (oleic acid, bovine albumin, glucose, and beef catalase); used to culture Mycobacteria
271
What is the Ziehl-Neelsen (ZN) stain used for?
staining acid-fast bacteria
272
What are the primary and counterstain used in the ZN technique?
basic carbolfuchsin (primary), methylene blue (counterstain)
273
What is the decolorizer used in the ZN technique (include formulation)?
acid alcohol (3% HCl + 95% alcohol)
274
How is a ZN stain interpreted?
acid-fast organisms appear bright red; non-acid-fast organisms, as well as the background, will appear blue
275
How does the Kinyoun method differ from the ZN method?
different formulation of carbolfuchsin is used - contains phenol, which helps the stain better penetrate the bacterial cell wall, and eliminates the need for heat during the staining process
276
What special equipment is needed for the fluorochrome staining method?
fluorescent microscope
277
What is the primary stain in the fluorochrome method?
Auramine O, or Auramine-Rhodamine
278
What is the decolorizer in the fluorochrome method (include formulation)?
acid alcohol (70% ethyl alcohol + 3% concentrated HCl)
279
What two counterstains can be used in the fluorochrome method, and what does the end result look like?
acridine-orange (yellow-green organisms against an orange background) or potassium permanganate (yellow-green organisms against a purple-black background - preferred)
280
What are the five nutritional requirements of bacteria and what are they needed for?
carbon (making cellular constituents); nitrogen (making protein); energy source (ATP for cellular functions); phosphates (nucleic acids); variety of metals and ions (enzymatic activity)
281
What is a differential stain?
stain that uses more than one dye and a decolorizer, as a means of differentiating microorganisms
282
How can E. coli be differentiated from K. pneumoniae biochemically?
E. coli is citrate =, indole +; K. pneumoniae is the opposite
283
How can S. salivarius be differentiated from S. pneumoniae biochemically?
S. salivarius is = for optochin, S. pneumoniae is susceptible
284
How can P. vulgaris be differentiated from P. mirabilis biochemically?
P. vulgaris is citrate =, indole +; P. mirabilis is the opposite
285
How can Aeromonas species be differentiated from Vibrio species biochemically?
Aeromonas is usually surrounded by beta-hemolysis on SBA; Vibrio is not
286
How can Bacillus species be differentiated from Staphylococcus species?
Bacillus are large, Gram+ rods that form endospores; Staph are Gram+, non-motile cocci that typically appear in clusters
287
How can M. kansasii be differentiated from M. flavascens?
M. kansasii is a photochromogen; M. flavescens is a scotochromogen
288
How can C. freundii be differentiated from C. diversus biochemically?
C. freundii produces H2S in TSI tubes; C. diversus does not
289
How can H2S+ E. coli be differentiated from Edwardsiella tarda biochemically?
E. coli on MacConkey is dry, dark pink, and smells like buttermilk; E. tarda on MacConkey is clear
