MCQs Bacteriology (1-10): With Answers and Explanations

  1. The identification of bacteria by serologic tests is based on the presence of specific antigens. Which of the following bacterial components is least likely to contain useful antigens?
    a. Capsule
    b. Cell wall
    c. Flagella
    d. Ribosomes
  2. Each of the following statements concerning the Gram stain is correct except:
    a. Escherichia coli stains pink because it has a thin peptidoglycan layer
    b. Streptococcus pyogens stains blue because it has a thick peptidoglycan layer
    Mycoplasma pneumoniae is not visible in the Gram’s stain because it does not have a cell wall
    d. Mycobacterium tuberculosis stain blue because it has a thick lipid layer
  3. An outbreak of sepsis caused by Staphylococcus aureus has occurred in the newborn nursery. You are called upon to investigate. According to your knowledge of the normal flora, what is the most likely source of the organism?
    a. Nose
    b. Colon
    c. Hand
    d. Throat
  4. Each of the following organisms is an important cause of urinary tract infections except:
    a. Klebsiella pneumoniae
    b. Escherichia coli
    c. Bacteriodes fragilis
    d. Proteus mirabilis
  5. A 30-year woman has non-bloody diarrhea for the past 14 hours. Which one of the following organisms is least likely to cause this illness?
    a. Streptococcus pyogens
    b. Clostridiodes difficile
    c. Shigella dysenteriae
    d. Salmonella enteritidis
  6. Each of the following agents is a recognized cause of diarrhea except
    a. Clostridium perfringens
    b. Vibrio cholerae
    c. Enterococcus faecalis
    d. Escherichia coli
  7. Each of the following statements about the classification of streptococci is correct except
    a. Pneumococci (Streptococcus pneumoniae) are alpha-hemolytic and can be serotyped on the basis of their polysaccharide capsule
    b. Enterococci are group D streptococci and can be classified by their ability to grow 6.5% sodium chloride
    c. Viridans streptococci are identified by Lancefield grouping, which is based on the C carbohydrate in the cell wall
    d. Although pneumococci and the viridans streptococci are alpha-hemolytic, they can be differentiated by the bile solubility test and their susceptibility to optochin
  8. Which of the following bacteria has the lowest 50% infective dose (ID50)?
    a. Campylobacter jejuni
    b. Salmonella typhi
    c. Vibrio cholerae
    d. Shigella sonnei
  9. Which of the following disease is best diagnosed by serologic means?
    a. Pulmonary tuberculosis
    b. Gonorrhea
    c. Actinomycosis
    d. Q Fever
  10. The coagulase test is used to differentiate
    a. Staphylococcus epidermidis from Neisseria meningitidis
    b. Staphylococcus aureus from Staphylococcus epidermidis
    c. Streptococcus pyogens from Staphylococcus aureus
    d. Streptococcus pyogens from Enterococcus faecalis

Answer Key for MCQ Microbiology:

  1. d (Ribosomes)
  2. d (Mycobacterium tuberculosis stains blue because it has a thick lipid layer)
  3. a (Nose)
  4. c (Bacteriodes fragilis)
  5. a (Streptococcus pyogens)
  6. c (Enterococcus faecalis)
  7. c (Viridans streptococci are identified by Lancefield grouping, which is based on the C carbohydrate in the cell wall)
  8. d (Shigella sonnei)
  9. d (Q Fever)
  10. b (Staphylococcus aureus from Staphylococcus epidermidis)

Acharya Tankeshwar

Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. As an asst. professor, I am teaching microbiology and immunology to medical and nursing students at PAHS, Nepal. I have been working as a microbiologist at Patan hospital for more than 10 years.

7 thoughts on “MCQs Bacteriology (1-10): With Answers and Explanations

  1. 1.a
    2.b (but, as i have known, Gram stain doesn’t give color because of Peptidoglycan layer. Gram stain stains cell on the basis of lipid content on cell wall.)
    4. i think it’s a. But option d is also susceptible.
    6.c (is it correct?)

  2. The blood exam of a patient with brucellosis and toxoplasmosis positive results required by physician for blood culture and in culture proteous has been grown why the real factor of brucellosis which is brucella not grown and this has been repeated many times. I do need your consults regarding the issue.
    Thanks for your attention

    1. Proteus give blood culture positive within 24 hours of incubation. While brucella required long incubation period as up to 14 days. Patient may have bacterimia with both bacteria and proteus overcome brucella growth in blood bottle.

    1. Dear Narayan
      Sorry for the inconvenience caused. Can you please help me by providing specific information, which key is wrong. We will correct it ASAP.

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