microbiology a systems approach test bank

Correct Answer: A

Rationale: The correct answer is A: Streptococcus pyogenes. This bacterium is the most likely causative agent due to its characteristic features. Streptococcus pyogenes is Gram-positive cocci in chains, which matches the description provided in the question. It is also known to be beta-hemolytic, causing complete lysis of red blood cells on blood agar. Streptococcus pyogenes is a common pathogen causing sore throat, often associated with pharyngitis. Explanation for incorrect choices: B: Streptococcus pneumoniae - This bacterium is Gram-positive but usually occurs in pairs (diplococci) and is alpha-hemolytic. C: Enterococcus faecalis - This bacterium is Gram-positive cocci but is not typically beta-hemolytic and is not commonly associated with sore throat infections. D: Staphylococcus aureus - This bacterium is Gram-positive cocci but usually occurs in clusters and

Correct Answer: D

Rationale: The correct answer is D: Sporotrichosis. Sporotrichosis is caused by the fungus Sporothrix schenckii, which commonly presents as a subcutaneous infection. In the given case, the presence of a small abscess with yellowish-green pus containing white granules is indicative of sporotrichosis. The histological examination showing drusen of a fungus, plasmatic and xanthome cells, and macrophages further supports the diagnosis of sporotrichosis. Choice A: Actinomycosis is a bacterial infection caused by Actinomyces species, not a fungal infection. Choice B: Aspergillosis is caused by Aspergillus species and typically presents as a pulmonary infection, not a subcutaneous abscess as described in the case. Choice C: Candidosis is caused by Candida species and usually presents as mucocutaneous infections, not a subcutaneous abscess with the

Correct Answer: A

Rationale: The correct answer is A: Streptococcus pneumoniae. This bacterium is known for producing a capsule that helps it evade the immune system. The capsule acts as a protective barrier, making it difficult for the immune system to recognize and attack the bacteria. Streptococcus pneumoniae is a common cause of pneumonia and meningitis. Explanation for why other choices are incorrect: B: Escherichia coli does not typically produce a capsule for immune evasion. It is more commonly associated with gastrointestinal infections. C: Salmonella enterica also does not produce a capsule for immune evasion. It is known for causing foodborne illness. D: Bacillus subtilis is a soil bacterium that is not known for producing a capsule to avoid the immune system.

Correct Answer: D

Rationale: The correct answer is D: Adenovirus. Adenovirus commonly causes acute febrile pharyngitis and pharyngoconjunctival fever. Adenovirus is known to cause respiratory infections and can present with symptoms such as sore throat, fever, and conjunctivitis. VZV (Varicella-Zoster Virus) causes chickenpox and shingles, not these specific symptoms. Measles virus causes a systemic illness with characteristic rash, not typically pharyngitis. Rubella virus causes a mild febrile illness with rash, but not pharyngitis. Therefore, based on the clinical presentation described, adenovirus is the most likely cause.

Correct Answer: A

Rationale: The correct answer is A: Psittacosis. This disease is transmitted via aerosols containing dried bird droppings or respiratory secretions from infected birds. When these aerosols are inhaled, the bacteria causing psittacosis enter the respiratory system and infect the individual. - B: Shigellosis is transmitted through contaminated food or water, not via aerosols. - C: Leptospirosis is transmitted through contact with water, soil, or food contaminated with the urine of infected animals, not via aerosols. - D: Giardiasis is transmitted through ingesting contaminated food or water, not via aerosols. Therefore, Psittacosis is the only disease in the list that is transmitted via aerosols, making it the correct answer.