Microbiology Flashcards
Preanalytic Procedures #11
Which selective medium is used for the isolation of gram-positive cocci?
* Columbia CNA with 5% sheep blood
* Trypticase soy agar with 5% sheep blood
* Eosin Methylene Blue
* Modified Thayer-Martin
Columbia CNA with 5% sheep blood
Columbia CNA agar contains colistin and nalidixic acid, which inhibit most facultative gram-negative organisms. Eosin Methylene Blue is selective and inhibits gram-positive organisms, and modified Thayer-Martin is selective and inhibits gram-positive organisms, gram-negative bacilli, and yeast. Trypticase Soy Agar medium with 5% sheep blood is not a selective medium
Preanalytic Procedures #16
Which of the following is the most appropriate specimen source and primary media selection?
* CSF: Columbia CNA, MacConkey
* Endocervical: Chocolate, Martin Lewis
* Sputum: Sheep Blood, Thayer-Martin, KV-laked blood
* Urine: Sheep Blood, Chocolate, Columbia CNA
Endocervical: Chocolate, Martin Lewis
Chocolate agar and chocolate agar-based selective media (Martin Lewis) are routinely used for the recovery of Neisseria gonorrhoeaefrom genital specimens. Sputum and urine specimens are routinely processed using a general purpose media (blood agar) and a selective agar (EMB or MacConkey). In addition, respiratory specimen cultures routinely include chocolate agar to enhance recovery of fastidious organisms such as Haemophilus influenzae.CSF is routinely processed using blood and chocolate agars.
Preanalytic Procedures #18
A Gram stain from the swab of a hand wound reveals:
- moderate neutrophils
- no squamous epithelial cells
- moderate gram-positive cocci in clusters
- moderate large gram-negative bacilli
Select the appropriate media that will selectively isolate each organism:
* KV-laked agar, Thayer-Martin
* Sheep Blood, MacConkey
* Columbia CNA, Chocolate
* Columbia CNA, MacConkey
Columbia CNA, MacConkey
Preanalytic Procedures #21
Media used to support growth of Legionella pneumophila should contain the additives:
* X and V factors
* Hemin and vitamin K
* Charcoal and yeast extract
* Dextrose and laked blood
Charcoal and yeast extract
Preanalytic Procedures #22
The best method for culture of Bordetella pertussis is:
* Phenylethyl alcohol agar
* Potassium tellurite blood agar
* Regan-Lowe agar
* Tinsdale agar
Regan-Lowe agar
Phenylethyl alcohol agar is selective for gram-positive cocci. Potassium tellurite agar and Tinsdale agar are selective/differential media useful in isolating Corynebacterium diphtheriae.
Preanalytic Procedures #26
A vaginal/rectal swab is collected from a pregnant patient to screen for Group B Streptococcus colonization. The best way to inoculate the medium to is:
* CNA agar
* LIM broth
* Sheep Blood agar
* Thioglycolate Broth
LIM Broth
Preanalytic Procedures #28
A wound specimen grows 2 colony types on Sheep Blood agar and 1 clear colony type on MAcConkey agar. Sheep Blood agar growth is documented as:
- Colony Type #1 swarming over entire plate, Gram Stain: Gram-negative bacilli
- Colony Type #2 white colony, Gram Stain: Gram-positive cocci in clusters
The best way to isolate colony type #2 from colony type #1 is to subculture:
* Colony #1 to Sheep Blood and Chocolate agars
* Colony #1 to Sheep Blood and/or MacConkey agar
* Colony #2 to Sheep Blood and Chocolate agars
* Colony #2 to CNA and/or PEA agar
Colony #2 to CNA and/or PEA agar
Preanalytic Procedures #31
Appropriate culture requirements for a specimen from a patient suspected of having tularemia include:
* A media with cysteine such as buffered charcoal yeast extract agar
* Colistin nalidixic acid agar
* Mueller-Hinton agar with 5% sheep blood agar
* Regan-Lowe media
A media with cysteine such as buffered charcoal yeast extract
Francisella tularensis is the causative agent of tularemia. It has a specific growth requirement of cysteine.
Preanalytic Procedures #32
The primary isolation of Neisseria gonorrhoeae requires:
* Anaerobic conditions
* Starch media
* Carbon dioxide
* Blood agar
Carbon Dioxide
Analytic Procedures for Bacteriology #39
Relapsing fever in humans is caused by:
* Borrelia recurrentis
* Brucella abortus
* Leptospira interrogans
* Spirrilium minus
Borrelia recurrentis
Transmitted by the human body louse
Analytic Procedures for Bacteriology #41
The Gram stain from a blood culture shows gram-positive cocci in chains. The subcultured plates plates from the blood culture bottle shows no growth. Additional testing should be done to detect the presence of:
* Staphylococcus saprophyticus
* Aerococcus urinae
* Abiotrophia defectiva
* Streptococcus pneumoniae
Abiotrophia defectiva
Nutritionally deficient streptococci such as Abiotrophia do not grow on sheep blood agar without the addition of a Staphylococcus aureus streak, the addition of a pyridoxal disc, or inclusion of a chocolate agar plate. Each will ensure the growth of nutritionally variant streptococci.
Analytic Procedures for Bacteriology #42
Gram stain examination from a blood culture shows dark blue, spherical organisms in clusters. Growth on Sheep Blood agar shows small, round, pale yellow colonies. Further tests should include:
* Catalase production and agglutination test for Protein A
* Bacitracin susceptibility and latex grouping
* Oxidase and indole reactions
* Voges-Proskauer and methyl red reactions
Catalase production and agglutination test for Protein A
Analytic Procedures for Bacteriology #43
Gram-positive cocci in chains are seen on a Gram stain from a blood culture. The organism grows as a beta-hemolytic colony. Further tests that could be performed include:
* PYR, bacitracin, and hippurate
* Catalase and agglutination test for Protein A
* Oxidase and mass spectroscopy
* Voges-Proskauer and methyl red
PYR, bacitracin, and hippurate
Analytic Procedures for Bacteriology #65
A 25-year-old man who had recently worked as a steward on a transoceanic grain ship presented to the emergency room with high fever, diarrhea, and prostration. Axillary lymph nodes are hemorhhagic and enlarged. A Wright-Giemsa stain of the aspirate shows bacilli that are bipolar, resembling safety pins. The most likely identification of this organism is:
- Brucella melitensis
- Streptobacillus moniliformis
- Spirillum minus
- Yersinia pestis
*Yersinia pestis
Analytic Procedures for Bacteriology #66
Anaerobic gram-positive bacilli with subterminal spores are isolated from a peritoneal abscess. The colony has a swarming appearance. The most likely identification of this organism is:
- Bacillus cereus
- Clostridium septicum
- Eggerthella lenta
- Bifidobacterium dentium
Clostridium septicum
Bacillus cereus is not an anaerobic organism; Eggerthella (formerly Eubacterium) and Bifidobacterium are anaerobic gram-positive bacilli that do not form spores. Clostridium septicum froms subterminal spores, and the colony can swarm.
Analytic Procedures for Bacteriology #67
A Gram stain of a peritoneal fluid shows large gram-positive bacilli. There is 3+ growth on anaerobic media only, with colonies producing a double zone of hemolysis. To assist with the classic identification, the microbiologist could:
- Determine if the organism ferments glucose
- Perform the oxidase test
- Set up egg yolk agar plate
- Test for bile tolerance
Set up egg yolk agar plate
The Gram stain and double zone of hemolysis are characteristics of Clostridium perfringens. C. perfringens is lecithinase-positive on the egg yolk agar test for lecithinase and lipase.
Analytic Procedures for Bacteriology #68
An organism from a peritoneal abscess is isolated on kanamycin-vancomycin laked blood agar and grows black colonies on BBE agar. It is nonpigmented, catalase-positive, and indole-negative. The genus of this organism is:
- Acidaminococcus
- Bacteroides
- Porphyromonas
- Prevotella
Bacteroides
Bacteroides fragilis grows on BBE agar and, because it can hydrolyze esculin, produces black colonies. B. fragilis is also catalase-positive and indole-negative.
Analytic Procedures for Bacteriology #69
Thin, gram-negative bacilli with tapered ends isolated from an empyema specimen grow only on anaerobic sheep blood agar. They are found to be indole-positivem lipase-negative, and are inhibited by 20% bile. The most probable identification of the isolate would be:
- Bacteroides distasonis
- Prevotella melaninogenica
- Fusobacterium nucleatum
- Clostridium septicum
Fusobacterium nucleatum
Fusobacterium nucleatum is classically described as long, slender, gram-negative bacilli with tapered ends. Inhibition of growth by 20% bile and a positive indole reaction narrow the selection process.
Analytic Procedures for Bacteriology #103
The optimal incubator temperature for isolation of the Campyolbacter jejuni/coli group is:
* 4°C
* 20°C
* 25°C
* 42°C
42°C
Analytic Procedures for Bacteriology #105
A Gram stain of a touch prep of a gastric biopsy shows gram-negative bacillli that are slender and curved. The most likely pathogen is:
* Burkholderia cepacia
* Corynebacterium urealyticum
* Helicobacter pylori
* Pasteurella multocida
Helicobacter pylori
Analytic Procedures for Bacteriology #106
A very bloody stool is received by the laboratory. The following day a pathogenic strain of E.coli is isolated. Which sugar should this isolate be tested against to begin the identification process?
* Mannitol
* Sorbitol
* Lactose
* Arabinose
Sorbitol
Escherichia coli O157:H7 is unable to utilize sorbitol producing clear colonies on the agar, MacConkey with Sorbitol. Other strains of E.coli do utilize the sorbitol producin gpink colonies on the same agar.
Analytic Procedures for Bacteriology #119
While swimming in a lake near his home, a young boy cut his foot, and an infection developed. The culture grew a nonfastidious gram-negative, oxidase-positive, beta-hemolytic, motile bacilli that produced deoxyribonuclease (DNase). The most likely identification is:
* Enterobacter cloacae
* Serratia marcescens
* Aeromonas hydrophila
* Escherichia coli
Aeromonas hyrdophila
Enterobacteriaceae, such as E.coli, Serratia, and Enterobacter, are oxidase-negative. The only selection that is oxidase-positive is Aeromonas. *It is associated with wounds contaminated with water.
Analytic Procedures for Bacteriology #148
> 100,000 CFU/mL of a gram-negative bacilli are isolated on MacConkey from a urine specimen. Biochemical results are shown in this table:
Test — Result
Glucose — acid, gas produced
Indole — negative
Urea — positive
TDA — positive
H2S — positive
The organism is most likely:
* Morganella morganii
* Proteus mirabilis
* Proteus vulgaris
* Providencia stuartii
Proteus mirabilis
Morganella and Providencia do not produce H2S; the indole reaction differentiates P.mirabilis and P.vulgaris
Analytic Procedures for Bacteriology #149
A urine culture has the results shown in this table:
Test — Result
* Sheep Blood — Swarming
* Columbia CNA — No Growth
* MacConkey — >100,000 CFU/mL, non-lactose-fermenter
* MacConkey — >100,000 CFU/mL, non-lactose-fermenter, with red pigment
The isolates from MacConkey agar have the biochemical reactions shown in this second table:
Test — Isolate 1 — Isolate 2
* TSI — alk/acid — alk/acid
* Urea — positive — negative
* TDA — positive — negative
* H2S — positive — negative
The organisms are most likely:
* Proteus vulgaris and Enterobacter cloacae
* Proteus mirabilis and Serratia marcascens
* Morganella morganii and Klebsiella pneumoniae
* Providencia stuartii and Serratia liquefaciens
Proteus mirabilis and Serratia marcascens
Serratia can produce a red pigment; Proteus mirabilis swarms, is TDA-positive and produces H2S.
