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: D

Rationale: Step 1: Formic acid is produced during fermentation by Actinomyces. Step 2: Actinomyces are known to produce organic acids like formic acid through fermentation. Step 3: Other choices like Streptococcus, Klebsiella, and Clostridium are not typically associated with formic acid production. Step 4: Actinomyces is the most likely candidate based on its fermentation capabilities. Summary: Actinomyces is the correct answer because it is known to produce formic acid during fermentation, while the other choices lack this specific metabolic function.

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: A

Rationale: The correct answer is A: Head lice. Epidemic typhus is transmitted by the body louse, Pediculus humanus humanus, which is different from the head louse, Pediculus humanus capitis. Head lice are not known to transmit epidemic typhus. Body lice are the primary vectors for transmitting epidemic typhus. Fleas are vectors for other diseases such as plague, not epidemic typhus. Ticks are vectors for various diseases but not for epidemic typhus. Therefore, the correct vector for epidemic typhus transmission is body lice, making choice A the correct answer.

Correct Answer: A

Rationale: The most likely diagnosis is Epidemic typhus (Choice A) based on the symptoms described. The presence of roseolous-petechial rash, high fever (41oC), hyperemia of face, reddening of scleras, tremor of the tongue, tachycardia, and splenomegaly are classic signs of epidemic typhus. The rash typically appears around the 5th day of the disease. Summary: - B: Measles typically presents with a maculopapular rash starting on the face and spreading downward. It doesn't usually present with tremor of the tongue or splenomegaly. - C: Alcohol delirium is characterized by confusion, disorientation, and hallucinations due to alcohol consumption. It doesn't match the symptoms described. - D: Leptospirosis presents with fever, muscle pain, and conjunctival suffusion. It doesn't typically present with the specific rash and trem