microbiology an introduction 13th edition test bank

Correct Answer: A

Rationale: The correct answer is A: Streptococcus pyogenes. Rationale: 1. Gram-positive cocci in chains: S. pyogenes is a Gram-positive cocci in chains. 2. Catalase-negative: S. pyogenes is catalase-negative. 3. Beta-hemolytic: S. pyogenes exhibits beta-hemolysis. Summary of other choices: B: Streptococcus pneumoniae is alpha-hemolytic and optochin-sensitive. C: Enterococcus faecalis is catalase-negative, but not typically beta-hemolytic. D: Staphylococcus aureus is catalase-positive and coagulase-positive.

Correct Answer: A

Rationale: The correct answer is A: Staphylococcus epidermidis. The presence of Gram-positive cocci arranged in clusters, catalase-positive, and coagulase-negative characteristics are indicative of Staphylococcus species. Staphylococcus epidermidis is a common skin commensal that causes wound infections. Staphylococcus aureus is coagulase-positive and often causes more aggressive infections. Streptococcus pyogenes is catalase-negative and typically forms chains, not clusters. Enterococcus faecalis is catalase-negative and commonly found in the GI tract, not a common cause of wound infections.

Correct Answer: A

Rationale: The correct answer is A: Escherichia coli. E. coli is a Gram-negative rod that typically has a greenish hue on MacConkey agar due to its ability to ferment lactose, producing acid that changes the pH indicator to green. E. coli is a common cause of diarrhea, particularly in cases of traveler's diarrhea. Salmonella (B), Shigella (C), and Klebsiella (D) are also Gram-negative rods but do not typically show a greenish hue on MacConkey agar and are less commonly associated with causing diarrhea compared to E. coli.

Correct Answer: A

Rationale: The correct answer is A: Corynebacterium diphtheriae. This bacterium causes diphtheria, characterized by a grayish pseudomembrane in the throat. The dark blue-staining rods with polar granules seen in microscopic examination are known as metachromatic granules, which are specific to Corynebacterium diphtheriae. Streptococcus pyogenes (choice B) causes strep throat but does not produce pseudomembranes. Haemophilus influenzae (choice C) can cause respiratory infections but does not typically present with a pseudomembrane. Neisseria gonorrhoeae (choice D) is a sexually transmitted bacterium and is not associated with the symptoms described.

Correct Answer: A

Rationale: The most likely diagnosis is Actinomycosis. This is because the patient's presentation of a painful swelling with a fistula containing white granules and yellow-green honeycomb-like tissue is classic for Actinomycosis. Actinomyces is a gram-positive anaerobic bacterium that forms sulfur granules in tissues. Tuberculosis (B) typically presents with caseating granulomas, not sulfur granules. Leprosy (C) presents with skin lesions and nerve damage, not characteristic of this case. Syphilis (D) usually presents with painless ulcers and rash, not the painful swelling and fistula seen in this patient.