medical microbiology test bank

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Microscopic examination of vaginal discharge revealed pear-shaped flagellated protozoa with an undulating membrane. What is the causative agent?

  • A. Trichomonas vaginalis
  • B. Giardia lamblia
  • C. Trypanosoma brucei
  • D. Leishmania donovani
Correct Answer: A

Rationale: The correct answer is A: Trichomonas vaginalis. Trichomonas vaginalis is a sexually transmitted protozoan that causes trichomoniasis. The pear-shaped flagellated protozoa with an undulating membrane described in the question match the morphology of Trichomonas vaginalis. It is typically found in vaginal discharge of infected individuals. Giardia lamblia (B) is a different protozoan that causes giardiasis and has a distinct morphology of a teardrop shape with flagella. Trypanosoma brucei (C) causes African sleeping sickness and Leishmania donovani (D) causes visceral leishmaniasis, both of which have different morphologies and clinical presentations compared to Trichomonas vaginalis.

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Brown algae are commonly referred to as:

  • A. Phaeophyta
  • B. Rhodophyta
  • C. Chrysophyta
  • D. Phaeophyta
Correct Answer: A

Rationale: The correct answer is A: Phaeophyta. Brown algae are commonly referred to as Phaeophyta because they contain brown pigments like fucoxanthin. Rhodophyta (B) refers to red algae, Chrysophyta (C) to golden algae, and D repeats the same term as A. Therefore, A is the correct choice based on the distinctive pigments present in brown algae.

The time in minutes in which 90% of the bacterial population will be killed at a given temperature is called the

  • A. generation time.
  • B. thermal death time.
  • C. sterilization time.
  • D. decimal reduction time.
Correct Answer: D

Rationale: The correct answer is D: decimal reduction time. This term represents the time required at a specific temperature to kill 90% of a bacterial population. It is a key parameter in microbiology to determine the effectiveness of a given heat treatment. Generation time (A) refers to the time it takes for a population to double in size. Thermal death time (B) is the shortest time needed to kill all organisms at a specific temperature. Sterilization time (C) is a general term and does not specifically refer to the time required to kill 90% of the population.

A smear stained by Burri-Gins method revealed a mucous structure tightly bound to the bacterial cell wall. What is this structure called?

  • A. Capsule
  • B. Spore
  • C. Flagella
  • D. Filament
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.

RNA viruses belong to which of the following types according to the Baltimore classification system?

  • A. I, II, III
  • B. II, III, IV
  • C. I, IV, V
  • D. III, IV, V
Correct Answer: D

Rationale: The correct answer is D: III, IV, V.

1. RNA viruses belong to Group III of the Baltimore classification system because their genetic material is single-stranded RNA.
2. They are also categorized under Group IV as they use reverse transcriptase to replicate their genetic material.
3. Finally, RNA viruses fall under Group V as they have an envelope derived from the host cell membrane.
Therefore, options A, B, and C are incorrect as they do not include all the correct groups that RNA viruses belong to according to the Baltimore classification system.

The bacitracin sensitivity test demonstrates

  • A. staphylococci
  • B. pneumococci
  • C. intestinal bacteria
  • D. group A streptococci
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.