medical microbiology test bank

Correct Answer: D

Rationale: The bacitracin sensitivity test is used to differentiate between different types of streptococci. Group A streptococci are sensitive to bacitracin, which means they will show inhibition around the bacitracin disk. This sensitivity is a characteristic feature of group A streptococci and helps in their identification. Staphylococci, pneumococci, and intestinal bacteria do not exhibit this sensitivity to bacitracin. Therefore, the correct answer is D: group A streptococci.

Correct Answer: C

Rationale: The correct answer is C: Weakly bound to the cell wall. The glycocalyx in bacteria is a protective layer that can be loosely attached to the cell wall or membrane. This loose attachment allows for flexibility and protection against desiccation and immune responses. Choice A is incorrect because the glycocalyx is not strongly bound to the cell wall, as it needs to be able to be shed easily for bacteria to escape host immune responses. Choice B is incorrect because the glycocalyx is not directly involved in bacterial movement, but rather serves as a protective barrier. Choice D is incorrect as the glycocalyx does play a role in bacterial physiology.

Correct Answer: A

Rationale: The correct answer is A: Oxacillin. In AST for Gram-positive bacteria, the antibiotic panel typically includes oxacillin to determine if the bacterium is susceptible or resistant to beta-lactam antibiotics. Oxacillin is commonly used to test for methicillin resistance in Staphylococcus aureus. Tetracycline (B), Tobramycin (C), and Amikacin (D) are not typically included in the Gram-positive antibiotic panel. Tetracycline is more commonly used for Gram-negative bacteria, while Tobramycin and Amikacin are aminoglycosides usually tested in Gram-negative bacterial infections. Therefore, they are not appropriate choices for the Gram-positive antibiotic panel.

Correct Answer: A

Rationale: Saddle nose is a condition where the bridge of the nose collapses, a characteristic feature of congenital syphilis. This occurs due to inflammation and destruction of cartilage. Syphilis is caused by the bacterium Treponema pallidum. CMV, Rubella, and Toxoplasmosis do not typically cause saddle nose. CMV can result in hearing loss, Rubella can lead to cataracts and heart defects, and Toxoplasmosis may cause hydrocephalus or chorioretinitis.

Correct Answer: C

Rationale: To calculate the total magnification, we multiply the magnification of the ocular lens by the magnification of the objective lens. In this case, 10 (ocular) x 40 (objective) = 400. This is why choice C (400) is correct. Choices A, B, and D are incorrect because they do not represent the correct calculation of total magnification based on the given magnification powers of the ocular and objective lenses.