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. Capsuleb. Cell wallc. Flagellad. Ribosomes
2. **Each of the following statements concerning the Gram stain is correct except:**a. Escherichia colistains pink because it has a thin peptidoglycan layerb. Streptococcus pyogens stains blue because it has a thick peptidoglycan layerc Mycoplasma pneumoniae is not visible in the Gram’s stain because it does not have a cell walld. Mycobacterium tuberculosisstain blue because it has a thick lipid layer
3. **An outbreak of sepsis caused byStaphylococcus aureushas 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. Noseb. Colonc. Handd. Throat
4. **Each of the following organisms is an important cause of urinary tract infections except:**a. Klebsiella pneumoniaeb. Escherichia colic. Bacteriodes fragilisd. 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 pyogensb. Clostridiodes difficilec. Shigella dysenteriaed. Salmonella enteritidis
6. Each of the following agents is a recognized cause of diarrhea excepta. Clostridium perfringensb. Vibrio choleraec. Enterococcus faecalisd. Escherichia coli
7. Each of the following statements about the classification of streptococci is correct excepta. Pneumococci (Streptococcus pneumoniae) are alpha-hemolytic and can be serotyped on the basis of their polysaccharide capsuleb. Enterococci are group D streptococci and can be classified by their ability to grow 6.5% sodium chloridec. Viridans streptococci are identified by Lancefield grouping, which is based on the C carbohydrate in the cell walld. 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 jejunib. Salmonella typhic. Vibrio choleraed. Shigella sonnei
9. **Which of the following disease is best diagnosed by serologic means?**a. Pulmonary tuberculosisb. Gonorrheac. Actinomycosisd. Q Fever
10. The coagulase test is used to differentiatea. Staphylococcus epidermidisfrom Neisseria meningitidisb. Staphylococcus aureus from Staphylococcus epidermidisc. Streptococcus pyogens from Staphylococcus aureusd.Streptococcus pyogens from Enterococcus faecalis

Answer Key for MCQ Microbiology:

1. d (Ribosomes)
2. d (Mycobacterium tuberculosisstains 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)

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