microbiology basic and clinical principles test bank

Correct Answer: A

Rationale: Step 1: Gram-positive cocci in chains suggest Streptococcus species. Step 2: Catalase-negative eliminates Staphylococcus aureus. Step 3: Beta-hemolytic on blood agar matches Streptococcus pyogenes. Step 4: Streptococcus pyogenes is a common cause of sore throat (pharyngitis). Summary: A: Streptococcus pyogenes - Correct due to Gram-positive cocci in chains, catalase-negative, beta-hemolytic, and common cause of sore throat. B: Staphylococcus aureus - Incorrect due to catalase-positive. C: Streptococcus pneumoniae - Incorrect due to alpha-hemolytic. D: Enterococcus faecalis - Incorrect due to not being beta-hemolytic.

Correct Answer: A

Rationale: The correct answer is A: Amikacin sulfate. Pseudomonas aeruginosa is commonly resistant to many antibiotics, but aminoglycosides like Amikacin have good activity against it. Step 1: Identify the pathogen causing the infection. Step 2: Consider the antibiotic's spectrum of activity against the pathogen. Step 3: Choose an antibiotic with proven efficacy. Amikacin is a good choice due to its effectiveness against Pseudomonas. Choice B, Benzylpenicillin, is a penicillin which is not effective against Pseudomonas. Choice C, Cephazolin, is a cephalosporin with limited activity against Pseudomonas. Choice D, Erythromycin, is a macrolide which is not effective against Pseudomonas.

Correct Answer: A

Rationale: The correct answer is A: Delayed hypersensitivity reaction. In granuloma development in tuberculosis, macrophages present antigen to T cells, leading to a delayed hypersensitivity reaction. This triggers the recruitment of more macrophages and formation of granulomas. Antibody-dependent cytotoxicity (B) and complement-dependent cytotoxicity (C) involve antibodies and complement proteins in immediate hypersensitivity reactions, which are not the primary mechanisms in tuberculosis. Anaphylactic reaction (D) is an acute systemic allergic reaction mediated by IgE antibodies, not relevant to granuloma formation in tuberculosis.

Correct Answer: C

Rationale: The correct answer is Shigella (Choice C) because it matches the description of being Gram-negative rods and lactose non-fermenters. Shigella is a non-lactose fermenting, Gram-negative rod that typically produces colorless colonies on Endo agar. Salmonella (Choice A) and Escherichia coli (Choice B) are both lactose fermenters and would produce pink colonies on Endo agar. Proteus (Choice D) is also a lactose fermenter and would appear pink on Endo agar. Therefore, based on the characteristics provided, Shigella is the most likely microorganism in this scenario.

Correct Answer: D

Rationale: The correct answer is D, "All of these." Monotrichous bacteria have a single flagellum at one end, amphitrichous have flagella at both ends, and peritrichous have flagella distributed all over the surface. The answer D is correct because it includes all these possibilities based on flagella location. Monotrichous is incorrect as it only refers to a single flagellum, amphitrichous is incorrect as it only refers to flagella at both ends, and peritrichous is incorrect as it only refers to flagella all over the surface. Therefore, the correct answer encompasses all these options.