OpenStax Microbiology Test Bank

OpenStax Microbiology Test Bank Related

Review OpenStax Microbiology Test Bank related questions and content

A 36-year-old man provisionally diagnosed with renal tuberculosis has undergone urinary sediment analysis. Microscopy revealed acid-fast bacteria, but Pryce method detected no cord factor. Name the most reliable method of investigation that can confirm or refute this provisional diagnosis:

  • A. Inoculation of laboratory animals
  • B. Phage typing of the obtained culture
  • C. Allergy skin test
  • D. Toxigenicity testing
Correct Answer: B

Rationale: The correct answer is B: Phage typing of the obtained culture. This method is used for typing Mycobacterium tuberculosis strains based on susceptibility to specific bacteriophages. If the culture shows susceptibility, it confirms the presence of M. tuberculosis. In this case, the absence of cord factor indicates that the bacteria are unlikely to be M. tuberculosis.

Option A (Inoculation of laboratory animals) is unethical and not necessary when other methods are available. Option C (Allergy skin test) is not relevant for confirming a diagnosis of renal tuberculosis. Option D (Toxigenicity testing) is not specific for confirming or refuting a diagnosis of M. tuberculosis.

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A sample stained using Romanovsky-Giemsa method revealed crescent-shaped protozoa with pointed ends and blue cytoplasm. What is the causative agent?

  • A. Toxoplasma
  • B. Plasmodium
  • C. Leishmania
  • D. Trypanosoma
Correct Answer: A

Rationale: The correct answer is A: Toxoplasma. The crescent-shaped protozoa with pointed ends and blue cytoplasm described in the question are characteristic of Toxoplasma gondii, the causative agent of toxoplasmosis. Toxoplasma staining with Romanovsky-Giemsa method typically shows these specific morphological features. Plasmodium causes malaria and does not exhibit the described morphology. Leishmania and Trypanosoma are both kinetoplastid parasites, but they do not typically present as crescent-shaped protozoa with blue cytoplasm. Therefore, based on the specific characteristics described in the question, the correct answer is Toxoplasma.

Viruses can infect

  • A. plants.
  • B. bacteria.
  • C. animals.
  • D. all organisms.
Correct Answer: D

Rationale: The correct answer is D because viruses have the ability to infect all organisms, including plants, bacteria, animals, and even fungi. Viruses are non-living entities that require a host cell to replicate and spread. They can infect a wide range of organisms by attaching to specific receptors on the host cell's surface. Therefore, the correct answer is D as viruses have the capability to infect all living organisms. Choices A, B, and C are incorrect because viruses can infect not only plants, bacteria, and animals but also other organisms, making choice D the most comprehensive and accurate option.

Lipopolysaccharides (LPS) are found in:

  • A. Gram-positive bacteria
  • B. Fungal cell walls
  • C. Gram-negative bacterial outer membrane
  • D. Viral capsids
Correct Answer: C

Rationale: The correct answer is C: Gram-negative bacterial outer membrane. Lipopolysaccharides (LPS) are major components of the outer membrane of Gram-negative bacteria. LPS consist of lipid A, core oligosaccharide, and O-antigen. They play a crucial role in the structural integrity and protection of Gram-negative bacteria.

Choice A (Gram-positive bacteria) is incorrect because LPS are not present in Gram-positive bacteria. Choice B (Fungal cell walls) is incorrect as LPS are specific to bacterial outer membranes. Choice D (Viral capsids) is incorrect as LPS are not associated with viral structures.

A patient with a sore throat had a throat smear revealing Gram-positive cocci in pairs with a capsule. What is the most likely causative agent?

  • A. Streptococcus pneumoniae
  • B. Neisseria meningitidis
  • C. Haemophilus influenzae
  • D. Klebsiella pneumoniae
Correct Answer: A

Rationale: Rationale:
1. Gram-positive cocci in pairs indicate Streptococcus pneumoniae.
2. Presence of a capsule points to S. pneumoniae as it has a polysaccharide capsule.
3. S. pneumoniae commonly causes sore throat.
4. Neisseria meningitidis, Haemophilus influenzae, and Klebsiella pneumoniae are not typically associated with sore throat.

A 70-year-old man has developed prosphetic stomatitis. Apart of this he was found to have an evident lesion of mouth corners. Microscopical examination revealed large ovoid gram-positive cells. What microorganisms are most likely to be the leading etiological agent of such a lesion?

  • A. Candida fungi
  • B. Streptococci
  • C. Staphylococci
  • D. Neisseria
Correct Answer: A

Rationale: The correct answer is A: Candida fungi. In the context of a 70-year-old man with angular cheilitis (lesion at the corners of the mouth) and stomatitis, the presence of large ovoid gram-positive cells points towards Candida species, which are yeast fungi. Candida is a common opportunistic pathogen that can cause oral thrush and angular cheilitis in immunocompromised individuals, such as elderly people. Candida fungi are known to appear as large ovoid cells under microscopic examination.

Summary of other choices:
B: Streptococci are gram-positive bacteria and are not typically associated with large ovoid cells seen in this case.
C: Staphylococci are also gram-positive bacteria and are not known to present as large ovoid cells in this context.
D: Neisseria are gram-negative bacteria and are not the usual etiological agents for oral lesions like angular cheilitis.

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