medical microbiology test bank

Correct Answer: A

Rationale: The correct answer is A: Streptococcus pneumoniae. This bacterium is a common cause of pneumonia and is known to appear as Gram-positive cocci in pairs with a capsule. The presence of a capsule is a key characteristic of S. pneumoniae. Staphylococcus aureus (B) is a Gram-positive cocci but typically does not have a capsule. Neisseria meningitidis (C) is a Gram-negative diplococcus, not a Gram-positive cocci. Klebsiella pneumoniae (D) is a Gram-negative rod, not a Gram-positive cocci. Therefore, based on the staining pattern and the presence of a capsule, Streptococcus pneumoniae is the most likely causative agent in this case.

Correct Answer: B

Rationale: The correct answer is B: focal. When a pathogen spreads from the original site to other tissues or organs, it is considered a focal infection. This term specifically refers to an infection that is localized to a specific area but can spread to other parts of the body. A: Local infection refers to an infection that is confined to a specific area without spreading to other tissues or organs. C: Natural is not a term commonly used to describe the spread of pathogens within the body. D: Acute refers to the rapid onset of a disease but does not specifically address the spread of pathogens from one site to another. In summary, the term "focal" best describes the scenario provided in the question, making it the correct answer.

Correct Answer: B

Rationale: The correct answer is B because the AST reaction, or anti-streptolysin titer, is used in the diagnostic of post-streptococcal sequelae, such as rheumatic fever and glomerulonephritis. This test measures the level of antibodies produced by the body in response to Streptolysin O, a toxin produced by Group A Streptococcus bacteria. It helps in identifying if a patient has had a recent Streptococcus infection that could lead to these complications. A: Incorrect. The AST reaction does not require urine samples, but rather blood samples. C: Incorrect. The AST reaction specifically targets antibodies produced in response to Group A Streptococcus. D: Incorrect. The AST reaction does not directly identify isolated streptococci but rather measures the body's immune response to Streptolysin O.

Correct Answer: D

Rationale: The correct answer is D: Index of fecal coli-forms. Fecal coli-forms are bacteria found in the intestines of warm-blooded animals, including humans. Their presence in water indicates fecal contamination, which is a common source of hepatitis A transmission. Monitoring the index of fecal coli-forms can help identify potential sources of contamination and assess the risk of disease transmission. A: Number of coli-phages - Coli-phages are viruses that infect coliform bacteria and are not directly related to fecal contamination. B: Escherichia coli index - While E. coli is a type of coliform bacteria found in the intestines of warm-blooded animals, it alone may not be a reliable indicator of fecal contamination in water sources. C: Oxidability - Oxidability is a measure of the water's ability to react with oxygen and does not provide direct information about fecal contamination or the presence of pathogens like hepatitis A. In summary,

Correct Answer: A

Rationale: The correct answer is A: Capsule. The capsule is a mucous structure tightly bound to the bacterial cell wall. It helps bacteria evade the host immune system and provides protection. The other choices are incorrect because: B) Spores are resistant structures formed by some bacteria for survival, C) Flagella are long, whip-like structures for movement, and D) Filaments are long, thin structures found in some bacteria.