mastering microbiology test bank

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Antigenic variation is used by bacteria to:

  • A. evade host immune responses
  • B. increase antibiotic susceptibility
  • C. increase peptidoglycan synthesis
  • D. enhance motility
Correct Answer: A

Rationale: The correct answer is A: evade host immune responses. Antigenic variation allows bacteria to change their surface antigens, making it difficult for the host immune system to recognize and attack them effectively. This enhances the bacteria's ability to evade immune responses and establish infection.

B: Increase antibiotic susceptibility is incorrect because antigenic variation does not directly impact the susceptibility of bacteria to antibiotics.

C: Increase peptidoglycan synthesis is incorrect because antigenic variation is not related to the synthesis of peptidoglycan, which is a major component of the bacterial cell wall.

D: Enhance motility is incorrect because antigenic variation does not directly affect the motility of bacteria.

In summary, antigenic variation in bacteria primarily serves to help them evade host immune responses, making option A the correct answer.

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While examining the feces of a patient with diarrhea, cysts with four nuclei were found. What protozoan is most likely causing the condition?

  • A. Entamoeba histolytica
  • B. Lamblia
  • C. Trichomonas
  • D. Balantidium
Correct Answer: A

Rationale: The correct answer is A: Entamoeba histolytica. This protozoan causes amoebiasis, which presents with symptoms like diarrhea. The cysts with four nuclei found in the feces are characteristic of Entamoeba histolytica. This protozoan is known to cause invasive infection, leading to tissue destruction and ulcers in the intestines. Lamblia (choice B) typically presents with cysts containing two nuclei. Trichomonas (choice C) is a sexually transmitted parasite and does not form cysts. Balantidium (choice D) is a ciliated protozoan that does not have four nuclei in its cyst form.

Which of the following is a general-purpose medium?

  • A. Tryptic soy agar
  • B. Blood agar
  • C. Mannitol salt agar
  • D. MacConkey agar
Correct Answer: A

Rationale: The correct answer is A: Tryptic soy agar is a general-purpose medium suitable for cultivating a wide range of microorganisms. It provides essential nutrients for growth without inhibiting specific types of bacteria. Blood agar (B), Mannitol salt agar (C), and MacConkey agar (D) are selective or differential media designed to promote the growth of specific types of bacteria or differentiate between different bacterial species. Therefore, they are not considered general-purpose mediums.

The main function of bacterial ribosomes is:

  • A. DNA replication
  • B. protein synthesis
  • C. cell wall synthesis
  • D. RNA splicing
Correct Answer: B

Rationale: The correct answer is B: protein synthesis. Bacterial ribosomes are responsible for translating messenger RNA into proteins through a process called translation. Ribosomes are composed of both protein and RNA molecules and facilitate the binding of transfer RNA to the messenger RNA to assemble the amino acids in the correct order to form a protein. DNA replication (A) is carried out by enzymes such as DNA polymerase, not ribosomes. Cell wall synthesis (C) is a process involving enzymes that build the structure of the cell wall in bacteria. RNA splicing (D) is a eukaryotic process that involves removing introns from pre-mRNA molecules, which is not a function of bacterial ribosomes.

Production of RNA from DNA is called

  • A. Transposition
  • B. Translation
  • C. Transcription
  • D. RNA splicing
Correct Answer: C

Rationale: The correct answer is C: Transcription. Transcription is the process of synthesizing RNA from a DNA template. During transcription, RNA polymerase binds to the DNA and produces a complementary RNA strand. This process is essential for gene expression.

Explanation for why other choices are incorrect:
A: Transposition involves the movement of genetic elements within a genome, not the production of RNA from DNA.
B: Translation is the process of synthesizing proteins from mRNA, not the production of RNA from DNA.
D: RNA splicing is the process of removing introns and joining exons in pre-mRNA to produce mature mRNA, not the initial production of RNA from DNA.

Which bacteria produce exotoxins that can cause severe gastrointestinal illness?

  • A. Clostridium botulinum
  • B. Vibrio cholerae
  • C. Escherichia coli
  • D. All of the above
Correct Answer: D

Rationale: The correct answer is D, All of the above. Clostridium botulinum produces botulinum toxin causing botulism, Vibrio cholerae produces cholera toxin leading to severe diarrhea, and certain strains of Escherichia coli produce toxins causing gastrointestinal illness. Each bacterium has specific exotoxins that can result in severe gastrointestinal symptoms. Therefore, all three choices are correct in producing exotoxins that can cause severe gastrointestinal illness.

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