AP-Micro Microbiology: Bacteriology: Gram-Negative Identification 2 — Questions and Answers
Question 1: Which enzyme produced by Neisseria gonorrhoeae helps it evade complement-mediated killing?
- IgA protease (Correct answer)
- Beta-lactamase
- Catalase
- Coagulase
Correct answer: IgA protease
N. gonorrhoeae secretes IgA protease, which cleaves secretory IgA and also helps evade host mucosal immunity and complement.
Question 2: Which gram-negative rod is the most common cause of nosocomial urinary tract infections?
- Klebsiella pneumoniae
- Pseudomonas aeruginosa
- Escherichia coli (Correct answer)
- Proteus mirabilis
Correct answer: Escherichia coli
E. coli accounts for approximately 80% of community-acquired and 50%+ of nosocomial urinary tract infections.
Question 3: A gram-negative, oxidase-positive, non-fermenting rod growing at 42°C with a fruity odor is most likely:
- Acinetobacter baumannii
- Pseudomonas aeruginosa (Correct answer)
- Burkholderia cepacia
- Stenotrophomonas maltophilia
Correct answer: Pseudomonas aeruginosa
Pseudomonas aeruginosa is oxidase-positive, non-fermenting, grows at 42°C, and produces pyocyanin and a characteristic grape-like odor.
Question 4: The Voges-Proskauer (VP) test detects which end-product of glucose fermentation?
- Mixed acids
- Acetoin (Correct answer)
- Hydrogen sulfide
- Indole
Correct answer: Acetoin
The VP test detects acetoin (acetylmethylcarbinol), an intermediate in the butanediol fermentation pathway.
Question 5: Which gram-negative organism characteristically produces a green metallic sheen on EMB agar?
- Salmonella typhi
- Escherichia coli (Correct answer)
- Enterobacter aerogenes
- Klebsiella pneumoniae
Correct answer: Escherichia coli
Strong acid fermenters like E. coli produce a metallic green sheen on Eosin Methylene Blue (EMB) agar due to dye precipitation.
Question 6: Haemophilus influenzae requires which two growth factors supplied in chocolate agar?
- Factors I and II
- Factors V and X (Correct answer)
- Factors X and Y
- Factors II and V
Correct answer: Factors V and X
H. influenzae requires Factor V (NAD) and Factor X (hemin) for growth, both of which are released from lysed red blood cells in chocolate agar.
Question 7: Which characteristic distinguishes Shigella from Salmonella on triple sugar iron (TSI) agar?
- Shigella produces H2S; Salmonella does not
- Shigella ferments lactose; Salmonella does not
- Shigella produces no gas; Salmonella typically produces gas (Correct answer)
- Shigella alkalinizes the slant; Salmonella acidifies it
Correct answer: Shigella produces no gas; Salmonella typically produces gas
Shigella ferments glucose without gas production, while most Salmonella produce gas (CO2 and H2) from glucose fermentation.
AP-Micro Microbiology: Bacteriology: Gram-Negative Identification 2
Which enzyme produced by Neisseria gonorrhoeae helps it evade complement-mediated killing?