Microbiology Basic and Clinical Principles Test Bank

Correct Answer: B

Rationale: The correct answer is B: Malarial plasmodiums. The description of crescent bodies with a pointed end, blue cytoplasm, and red nucleus corresponds to the characteristics of Plasmodium species seen in Romanovsky's stain. Plasmodium species are known to cause malaria and have distinct features like the ones described. Incorrect choices: A: Toxoplasmas - Toxoplasma gondii typically appear as tachyzoites or bradyzoites under staining, not crescent bodies. C: Dermotropic leishmania - Leishmania species appear as amastigotes in tissue smears, not crescent bodies. D: Viscerotropic leishmania - Similar to choice C, Leishmania species do not typically present as crescent bodies in stained specimens.

Correct Answer: B

Rationale: The correct answer is B: Syphilis. The Wasserman reaction is a test for syphilis, specifically for detecting antibodies against the bacterium Treponema pallidum. In a 30-year-old man with a markedly positive Wasserman reaction, it indicates an active syphilis infection. Brucellosis (Choice A) is not diagnosed using the Wasserman reaction. Poliomyelitis (Choice C) is a viral infection affecting the spinal cord, not diagnosed using the Wasserman reaction. Influenza (Choice D) is a respiratory viral infection, not associated with the Wasserman reaction.

Correct Answer: D

Rationale: The correct answer is D: Propionibacterium acnes. This bacterium is not a fungus, but a common skin bacteria. Fungal vaginitis is typically caused by Candida albicans or other fungal species, not by bacteria like Escherichia coli, Streptococcus agalactiae, or Klebsiella oxytoca. Propionibacterium acnes is not associated with vaginal infections, making it the correct answer in this context.

Correct Answer: C

Rationale: The correct answer is Shigella (Choice C) because it matches the description of being Gram-negative rods and lactose non-fermenters. Shigella is a non-lactose fermenting, Gram-negative rod that typically produces colorless colonies on Endo agar. Salmonella (Choice A) and Escherichia coli (Choice B) are both lactose fermenters and would produce pink colonies on Endo agar. Proteus (Choice D) is also a lactose fermenter and would appear pink on Endo agar. Therefore, based on the characteristics provided, Shigella is the most likely microorganism in this scenario.

Correct Answer: A

Rationale: The correct answer is A: destruction of the local blood supply. In osteomyelitis, the infection occurs in the bone, which has a relatively poor blood supply compared to soft tissues. This limited blood flow makes it challenging for antibiotics to reach the infection site effectively, hindering their ability to combat the infection. Destruction of the local blood supply restricts the delivery of antibiotics and immune cells to the infected bone, leading to poor treatment outcomes. Summary: - Option A is correct because the limited blood supply in bones hinders antibiotic delivery. - Option B is incorrect as denaturing by normal flora does not impact antibiotic reach to the infection site. - Option C is incorrect as inflammation and edema, while present, do not primarily hinder antibiotic delivery. - Option D is incorrect as excessive pus production does not directly impede antibiotic access to the infection site.