Unit 4 Flashcards
Biochemical tests are based on the _______ of the microorganisms
Phenotype
Nucleic acid assays are based on the ______ of the organism and are believed to be more accurate
Genotype
The initial screening of gram-negative rods is done by testing for the use of this carbohydrate
Lactose
Other sugars used to differentiate bacteria include all of the following except
Sucralose
Bacteria can use carbohydrates by
Oxidation
Some bacteria are asaccharolytic. This means that these bacteria
Do not utilize any carbohydrate; instead they use other organic molecules for energy
During this process, glucose enters the glycolysis pathway, resulting in the formation of pyruvic acid, which is further oxidized to other acids. What is this process called?
Fermentation
Oxidative/fermentative (O/F) basal medium is a medium that will test the oxidative and fermentative capabilities of a microbe. The pH indicator is ______
Bromothymol blue
When performing the O/F test, one tube is covered with mineral oil and one tube is left uncovered. Why is one tube covered with mineral oil?
To create an anaerobic (fermentative) environment
A technician is reading the biochemical tests for identifying a particular gram-negative rod. The organism has produced acid, indicated by a color change, in the closed tube only. This indicates that the organism is
A fermenter
What are the sugars present in Triple sugar ion (TSI)?
Sucrose, glucose, and lactose
What chemicals are added to TSI to detect the production of hydrogen sulfide gas?
Ferrous sulfate and sodium thiosulfate
To inoculate TSI agar or Kilgore iron agar (KIA), the Laboratory scientist should pick a well-isolated colony with an inoculating needle and
Stab the butt almost all the way to the bottom of the tube, then move the needle back and forth over the surface of the slant all the way to the top of the tube
These bacteria are unable to ferment either lactose or glucose, but the can degrade the peptones present in the TSI agar or KIA aerobically, resulting in the production of alkaline by-products in the slant or deep, respectively, changing the indicator to a deep red color. What kind of bacteria cannot ferment lactose or glucose?
Nonfermenting bacilli
If an organism fermented glucose only and utilized peptones, what would the TSI reaction be?
Alkaline/acid
If bacterium utilizes lactose of sucrose, what will the TSI reaction look like?
Acid/acid
If a bacterium utlilizes lactose or sucrose and produces H2S, what will the TSI reaction look like?
Acid/acid, black butt
The test determines if an organism is a delayed lactose fermenter
O-nitrophenyl-B-D-galactopyranoside (ONPG) test
The chemical reaction for the ONPG test is
B-galactosidase hydrolyzes ONPG into galactose and o-nitrophenol ( yellow compound)
The methyl red test detects metabolic by products from what pathway/
Mixed acid fermentation pathway
The biochemical pathway that the methyl red test confirms is
Glucose —> pyruvic acid —>mixed acid fermentation
The two reagents used in the Vosges-Proskauer test are
40% KOH and a-naphthol
In the Voges-Proskauer test, you are testing for the metabolic by products of which pathway?
Glucose—>pyruvic acid — acetoin
The decarboxylase tests determine
Whether the bacteria possess enzymes capable of removing the carboxyl group of specific amino acids in the test medium
Decarboxylase tests exist for all the following amino acids except
Tyrosine
The medium used in the decarboxylase test is called
Moeller’s decarboxylae base medium
Why does the Moeller decarboxylase base medium contain glucose if it is testing the decarboxylation of amino acids?
Decarboxylase are inducible enzymes produced in an acid pH
Using Moeller’s decarboxylase base medium, what color is a positive reaction and what causes this color to be produced?
Purple, alkaline environment produced?
Bacteria demonstrating weak decarboxylase activity
May take up to 4 days to be positive
Amino acids can be metabolized by these substances that remove an amine group. What is this substance?
Deaminase
This test is useful in the initial differentiation of Proteus, Morganella, and Providencia species from the rest of the enterobacteriaceae
Phenylalanine deaminase
This reagent is used to demonstrate a positive phenylalanine deaminase test
10% ferric chloride
The principle of the citrate test includes all the following except
The pH indicator changes from red to bright yellow
A bacterial DNase is
An endonuclease that cleaves internal phosphodiester bonds, resulting in smaller subunits of DNA
Extracellular DNase can be produced by
Staphylcoccus aureus
Some bacteria produce these enzymes that break down gelatin into amino acids. These enzymes are called
Gelatinase
What amino acid is the substrate in indole test broth?
Tryptophan
What two reagents can be used to visualize indole in the broth?
Ehrlichs’s and Kovac’s
What type of medium is used in the motility test?
Semi-solid
A positive test for motility
Shows hazy appearance throughout or movement away from a stab
Nam the two reagents that are needed to visualize nitrite in the nitrate reduction test
N,N-dimethyl-a-naphthylamine and sulfanilic acid
What does the oxidase test determine?
The presence of the cytochrome oxidase system that oxidizes reduced cytochrome with molecular oxygen
What medium is used in the urease test?
Christensen media
What does a lysine iron agar (LIA) slant contain?
Lysine, glucose, ferric ammonium citrate and sodium thiosulfate
The LIA slant is also useful in differentiating
Proteus, Morganella, and Providencia
Commercial identification systems fall into all of the following categories except
Use of nitrogen and sulfur sources
How are organisms identified with commercial identification kits?
Numeric codes
This identification system for Enterobacteriaceae has a series of 20 cupules attached to a plastic strip. Inside the cupules are lyophilized pH based substrates. What is the name of this system?
API 20E
Rapid identification of clinical isolates often involves commercially packaged identification kits and fully automated instruments. What do these kits use to assess the preformed bacterial enzymes?
Chromogenic or fluorogenic substrates
What advantage do the methods based on enzyme substrates have over conventional methods?
They do not require growth of the organism in the system
Which of the following agars is not selective for enterobacteriaceae?
Buffered charcoal yeast extract
The primary pathogens of the enterobacteriaceae include all the following except
Proteus mirabilis
What organim presents as a pink colony with a halo on MAC agar and a green metallic sheen on eosin methylene blue (EMB) agar?
E. Coli
E. Coli strains have all the following properties except
Can use citrate as a sole carbon source
Which organism is the most common cause of UTI in humans?
E. Coli
All of the following are categories of diarrhea-causing E. Coli except
EMEC
The E. Coli stereotype O157:H7 is associated with all the following except
Liver damage
A microbiologist is reading a stool culture and notices a mucoid pink colony on MAC agar. What is the most likely organism?
Klebsiella pneumonia
All of the following are clinically significant isolates of the genes Enterobacter, except
E. Hartmanni
A DNase-positive member of the family enterbacteriaceae is suggestive of
Serratia
What bacterium produces swarming colonies on nonselective media, such as sheep blood agar (SBA)?
P. Mirabilis
The most important cause of UTIs is
E. Coli
What organism in the genus Providencia is incriminated in nonsocomial outbreaks in burn units and has been isolated from urine culture?
Providencia Stuartii
What genus has the following characteristics; urea negative, positive for lysine decarboxylase, hydrogen sulfide, and indole, and does not grow on Simmon citrate?
Edwardsiella
You have isolated a bacterium from a stool culture that produces clear colonies on sorbitol MacConkey (SMAC) agar. Which of the following would be the most appropriate test to perform next?
Rapid Mehtlyumbelliferyl-b-D-glucuronide (MUG)
What is the name of the organism that has been a documented cause of nursery outbreaks of neonatal meningitis and brain abscesses?
C. Koseri
All of the following are biochemical features of salmonella except
Lactose positive
Which animals are a common source of salmonellla serotypes?
Cold-blooded animals (fish)
What substance produced by the salmonella spp., causes pastroenteritis, has been implicated as a significant virulence factor?
Enterotoxin
What are the primary antigens used in serologic grouping of salmonellae?
Flagellar H antigen and somatic O antigen
What organism possess the Vi antigen?
Salmonella typhi
What disease produced by a salmonella spp. is a severe form of enteric fever?
Typhoid fever
All of the following are symptoms of salmonellosis that Marty appear 8-36 hour after ingestion of contaminated food except
Headache
Why is is the most cases of salmonella food poisoning are not treated with antibiotics?
The disease is self-limiting and will subside on its own
In carrier state, where are pathogenic salmonella carried?
Gallbladder
All of the following are characteristics of shigella spp. except
Urea positive
Bacillary dysentery caused but this organism is marker by penetration of intestinal epithelial cells following attachment of the organisms to mucosal surfaces, local inflammation, shedding of the intestinal lining, and formation of ulcers that follow the epithelial penetration. What is this organism?
Shigella
What bacterium is the causative agent of the plaque?
Yersinia pestis
What enteric organism may produce a blue-violet pigment on non-blood containing media?
Kluyvera
Why can direct microscopy not be used to provide a presumptive identification of the enteric bacteria?
The microscopic characteristics are indistinguishable from other gram-negative
A microbiologist is reading stool cultures plates. She is looking fr enteric pathogens on the MAC plate. What do they look like?
Clear, odorless colonies
A microbiologist is reading stool culture plates. She sees an organism that has a dry, pink colony with a surrounding “halo” of pink on MAC. What is a good presumptive identification of this organism?
Escherichia/citrobacter-like organism
A microbiologist is reading stool culture plates. She sees an organism that has a large, mucoid pink colony on MAC. What is a good presumptive identification of this organism?
Klebsiella/enterobacter-like organism
Which of the following is a curved, gram-negative rod that grow on thiosulfate citrate bile salts sucrose (TCBS) agar?
Vibrio
What is the name of the organism that causes the disease cholera?
V. Cholerae
Most infections caused by Vibrio cholerae are associated with
Ingestion of undercooked seafood
All of the following are biochemical characteristics of vibrio spp. except
Oxidase negative
What disease manifests in acute cases as a severe gastroenteriritis, accompanied by vomiting followed by diarrheic stools that described as rice water and occur 10-30 times a day?
Cholera
How is cholera treated?
Copious amounts of intravenous fluids
What is the name of the organism that is responsible for for “summer diarrhea” in japan?
V. Parahaemolyticus
Which of the following Vibrio species is most likely to be recovered from extraintestinal tract infections e.g. septicemia?
V. Vulnificus
What species of aeromonas is the most frequently associated with GI infections?
A caviae
Aermonads have been implicated in all the following disease except
Pneumonia
What do aeromonad colonies look like on cefsulodin-novobiocin (CIN) agar?
Pink colonies
What two biochemical tests help distinguish aeromonas spp. from other enterics?
Oxidase and indole
Aeromonas are generally susceptible to all these antimicrobial agents except
Ampicillin
All of the following characteristics describe the genus plesiomonas except
Oxidase negative
What environment is aeromonas spp. most commonly found in?
Fresh water
Most vibrio sp. are generally halophilic. However which one can also grow is an environment with 0% sodium chloride?
V. Cholerae
What is the name of the organism that is strongly associated with gastric, peptic, and duodenal ulcers, as well as GI carcinoma?
Helicobacter pylori
What organism may play a role in Guillain-Barré syndrome (GBS)?
Campylobacter
When collecting specimens that may contain campylobacter spp. bacteria, what transport medium should they be placed in, if a delay in transport is possible ?
Cary-Blair
CAMPY-BAP (blood agar plate) contains
Brucella agar base, 10% sheep RBCs, vanomycin, trimethoprim, polymyxin B, amphotericin B, and cephalothin
What temperature is an optimal growth temperature for campylobacter jejuni?
42C
What type of an atmosphere do campylobacters require for growth?
Microaerophilic and Capnophilic
What oraganim has a microscopic morphology of tiny, curved gram-negative rods, with S-shapes or seagull-wing shapes on gram stain?
Campylobacter
A Campy blood agar plate incubated at 42C from a stool exhibits colonies that are nonhemolytic, moist, “runny looking” and spreading. The gram stain shows tiny gram-negative rod with some S-shapes and seagull-wing shapes. What is growing on the plate?
Campylobacter
How is Helicobacter pylori presumptively identified?
A rapid urease test done on a gastric biopsy
What is the drug of choice for treating intestinal campylobacterosis?
Erythromycin
What biochemical test will differentiate nonfermenters from enterobacteriaceae (except pleisomonas)?
Oxidase
What substance do nonfermenters fail to ferment in traditional media?
Carbohydrates
All of the following are characteristics of pseudomonads except
Indole-positive
The three nonfermenters that make up the majority of isolates routinely seen in clinical laboratories include all of the following except
Pseudomonas putida
What pseudomonas sp. is the nonfermenter that is the leading cause of nosocomial pneumonia and bacteremia?
Pseudomonas aeruginosa
What organism is a common cause of pulmonary disease among individuals with cystic fibrosis?
P aeruginosa
All of the following are poor prognostic factors associated with pseudomonas aeruginosa bacteriemia except
Anemia
Which of the following is a virulence factor of pseudomonas aeruginosa?
All of the above
*endotoxin
*exotoxins
*capsule
An oxidase-positive, nonfermentative gram-negative bacillus that characteristically produces dry, wrinkled colonies describes
Pseudomonas stutzeri
A microbiologist is reading the plates from a sputum culture. On the sheep blood agar (SBA), the microbiologist sees the flat spreading colonies with a metallic sheen. On certified agar, a fluorescent green color is seen in the medium with clear colonies. On MacConkey, medium clear colonies are seen that have a fruity or grapelike odor. What is the most likely organism?
P. Aeruginosa
Psuedomonas aeruginosa is resistant to all the following antimicrobial agents except
Fluroquinolones
An H2S-positive, oxidase-positive, nonfermenters describes
Shewanella
Which gram-negative coccobacilli can appear as gram-positive cocci in smear made from blood cultures bottles?
Acinetobacter spp.
In what single setting does strenotrophomonas matophilia typically produce disease?
Nosocomial
What organism is associated with pneumonia in patients with cystic fibrosis or chronic granulomatous disease (CGD)?
Burkholderia capacia
What nonfermenter may produce a weak, slow, positive oxidase reaction?
Burkholderia cepacia
Which plant pathogen may be mistaken for Burkholeria cepacia?
Burkholderia gladioli
What is the causative agent of gleaners?
B. Mallei
What organisms causes melioidoisis?
B. Pseudomallei
Characteristics of most members of the family flavobacteriaceae
All of the above
*week fermenters
*cause of nosocomial infections
* ubiquitous in soil and water
Elizabetkingae meningosepticum causes all the following disease except
Gastroenteritis
Characteristics of Moraxella include
All of the above
*oxidase-positive and nonmotile
*biochemically inert ad aerobic
* susceptible to penicillin and opportunistic pathogens
Which nonfermenter is considered by government agencies to be a potential bioterroist agent?
Burkholderia mallei
A microbiologist is reading the plates from a sputum culture. The culture is from a patient with cystic fibrosis. One organism dominates the blood agar, chocolate, and MacConkey plates, The MacConkey plate shows an organism with a green pigment and a metallic sheen. The probable identification for this organism is
Pseudomonas aeruginosa
The bacterium is said to have a fruity or grapelike smell
Pseudomonas aeruginosa
All of the following are categories of bacterial growth requirements for oxygen and carbon dioxide except
Ambient air (95% O2 and 5% CO2)
What is anaerobe?
An organism that does not require oxygen to live
What is an obligate anaerobe?
An organism that grows only in the absence of molecular oxygen
What substances do organisms that use oxygen have to protect themselves from superoxide anions?
Superoxide dismutase and catalase
Anaerobes outnumber aerobes in all of the following locations, except
Skin
All of the following organisms are found on the skin under normal conditions except
Clostridium
All of the following organisms are found in the GI tract, except
Propionibacterium
Which of the following is characteristic of members of the genus Clostridium?
spore-forming anaerobic bacilli
What disease does clostridium perfringens cause?
Food poisoning
What disease does clostridium botulinum cause?
botulism
What disease does clostridium tetani cause?
Tetanus
What organism mostly commonly cause gas gangrene?
C. Perfringens
An older adult patient in a nursing home is recovering from bacterial pneumonia. The patient has been on a lengthy regiment of antimicrobial agents. Subsequently, the patient is diagnosed with pseudomemebranous colitis. What organism is the most likely cause?
Clostridium difficile
All of the following are non-spore forming, anaerobic, gram-positive bacilli, except
Clostridium
An immunosuppressed patient notices sinus tracts that are draining pus. He also notices that there appear to be small, hard “nuggets” int he pus. What disease is he mostly likely suffering from?
Actinomycosis
Bacterial vaginosis is a synergistic infectious process involving all the following bacteria except
Eubacterium
The four major groups of anaerobic gram-negative bacilli include all the following except
Mobiluncus
Which of the following bacteria is most likely the cause of tooth abscesses/
P. Gingivalis
What are two important factors that must be taken into consideration when transporting specimens for anaerobic culture?
Minimum exposure to oxygen and preventing drying out
Which of the following is considered a better specimen a better specimen for anaerobic culture than a swab?
Aspirate
All of the following procedures should be performed on clinical specimens to recover anaerobic bacteria, except
Kinyoun Stain
Gram stains of specimens for anaerobic cultures should be examined for all the following reasons except
The clinical and laboratory standards institute (CLSI) guidelines recommend gram stains on all anaerobic specimens
What is the ideal anaerobic incubation system?
Anaerobic chamber
How long are anaerobic cultures routinely held in the laboratory?
5-7 days
What evidence indicates the presence of anaerobes in cultures?
All of the above
How are suspected colonies of anaerobes processed?
All of the above
*gram stain morphology and reaction is observed
*an aerotolerance test is set up
*a pure culture/subculture place is inoculated and appropriate disks are added
How is the true gram stain reaction of an anaerobe determined?
Special potency disks
A vaginal swab is received for anaerobic culture. How should this request be handled or processed?
Contacts the physician, this is an unacceptable specimen
What disk is used to be presumptively identify peptostreptococcus anaerobius?
Sodium polyanethol sulfonate (SPS)
One egg-yolk agar, clostridium perfringens will demonstrate
Off white precipitate around colonies
An anaerobic culture reveals colonies with a double zone of hemolysis of SBA plate. There was no growth on plates incubated aerobically. The gram stain of that organism was a boxcar-shaped, gram-positive bacillus. What organisms is this?
Clostridium perfringens
Material from an intestinal abscess produces gray colonies with a brown color in the area around the colonies on a BBE plate incubated anaerobically. There is also a dark precipitate in the medium in the areas of heavy growth. A Gram stain of the colonies reveals gram-negative coccobacilli. What is the presumptive identification of this organism?
B. Fragilis
All of the following reasons are cited for performing antimicrobial susceptibility testing on anaerobes by the clinical and CLSI except
The determine the resistance mechanisms in anaerobes
All of the following are approaches to treating anaerobic infections except
Enzyme inactivators
What is the most common causative agent of gas gangrene?
Clostridium perfringens
How does clostridium difficile produce psuedomembrnous colitis and antibiotic-associated diarrhea?
Toxin A and toxin B (exotoxins_
After 24-hour incubation, an SBA from a vaginal culture reveals heavy growth of a-hemolytic, pinpoint rough colonies. A catalase test is performed and it is negative. What organism should you suspect?
Lactobacillus
