MCQ Written Exam 2023.

MCQ Written Exam 2023. Each of the following agents is a recognized cause of diarrhea except a. Clostridium perfringens b. Vibrio cholerae c. Enterococcus faecalis d. Escherichia coli - ANSWER c. Enterococcus faecalis 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 - ANSWER d. Ribosomes 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 pyogenes stains blue because it has a thick peptidoglycan layer c. Mycoplasma pneumoniae is not visible in the Gram's stain because it does not have a cell wall d. Mycobacterium tuberculosis stains blue because it has a thick lipid layer - ANSWER d. Mycobacterium tuberculosis stains blue because it has a thick lipid layer 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 - ANSWER a. Nose Each of the following organisms is an important cause of urinary tract infections except: a. Klebsiella pneumoniae b. Escherichia coli c. Bacteroides fragilis d. Proteus mirabilis - ANSWER c. Bacteroides fragilis A 30 year old woman has non-bloody diarrhea for the past 14 hours. Which one of the to following organisms is least likely to cause this illness? a. Streptococcus pyogenes b. Clostridium difficile c. Shigella dysenteriae d. Salmonella enteritidis - ANSWER a. Streptococcus pyogenes 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 - ANSWER c. Viridans streptococci are identified by Lancefield grouping which is based on the C carbohydrate in the cell wall Which of the following bacteria has the lowest 50% infective dose (ID50)? a. Campylobacter jejuni b. Salmonella typhi c. Vibrio cholerae d. Shigella sonnei - ANSWER d. Shigella sonnei