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Which bacteria produce urease enzyme to neutralize stomach acid?
- A. Salmonella typhi
- B. Escherichia coli
- C. Helicobacter pylori
- D. Shigella flexneri
Correct Answer: C
Rationale: Rationale:
1. Helicobacter pylori is known for producing urease enzyme to neutralize stomach acid.
2. Urease enzyme converts urea into ammonia, buffering the acidic pH.
3. This adaptation allows H. pylori to survive in the acidic environment of the stomach.
4. Salmonella typhi, Escherichia coli, and Shigella flexneri do not produce urease.
5. Therefore, C is the correct answer based on the unique urease-producing capability of H. pylori.
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The one-way transfer of genetic material from a donor cell to a recipient cell by direct cell-to-cell contact is:
- A. transformation
- B. transduction
- C. replication
- D. conjugation
Correct Answer: D
Rationale: Conjugation involves direct cell-to-cell contact for the transfer of genetic material, typically through a pilus. This process is well-documented in bacterial genetics. Transformation (A) involves uptake of free DNA from the environment. Transduction (B) is genetic transfer by a viral vector. Replication (C) is the process of producing identical copies of DNA or RNA. Therefore, the correct answer is D (conjugation) as it specifically refers to the one-way transfer of genetic material through direct cell-to-cell contact.
A 4 year old child had Mantoux test. 60 hours after tuberculin introduction a focal skin hardening and redness 15 mm in diameter appeared. It was regarded as positive test. What type of hypersensitivity reaction is this test based upon?
- A. Delayed-type hypersensitivity
- B. Immune complex-mediated hypersensitivity
- C. Complement-mediated cytotoxic hypersensitivity
- D. Immediate hypersensitivity
Correct Answer: A
Rationale: The correct answer is A: Delayed-type hypersensitivity. The Mantoux test is a type IV hypersensitivity reaction, which is also known as delayed-type hypersensitivity. This reaction typically occurs 48-72 hours after exposure to an antigen, such as tuberculin in this case. The focal skin hardening and redness that appeared 60 hours after tuberculin introduction align with the timeline and characteristics of a delayed-type hypersensitivity reaction.
Summary:
- Choice A (Delayed-type hypersensitivity): Correct, as explained above.
- Choice B (Immune complex-mediated hypersensitivity): Incorrect, as this reaction involves immune complexes and typically presents with tissue damage and inflammation.
- Choice C (Complement-mediated cytotoxic hypersensitivity): Incorrect, as this reaction involves the activation of complement proteins leading to cell lysis.
- Choice D (Immediate hypersensitivity): Incorrect, as this reaction, such as in allergies, occurs within minutes to hours of exposure to an antigen and involves IgE-mediated mast
The pertussis toxin:
- A. Changes the protein synthesis
- B. Provokes overproduction of mucus in the tracheal cells
- C. Changes the adenylate cyclase-mediated conversion of ATP to cyclic AMP
- D. Provokes release of electrolytes
Correct Answer: C
Rationale: The pertussis toxin inhibits the adenylate cyclase-mediated conversion of ATP to cyclic AMP, leading to decreased levels of cyclic AMP in the cell. This disrupts important cellular signaling pathways, affecting immune response and causing symptoms of pertussis. Choices A, B, and D are incorrect because the pertussis toxin does not directly affect protein synthesis, provoke overproduction of mucus in tracheal cells, or provoke release of electrolytes.
Which bacteria are most commonly associated with hospital-acquired infections?
- A. Staphylococcus aureus
- B. Escherichia coli
- C. Klebsiella pneumoniae
- D. All of the above
Correct Answer: D
Rationale: The correct answer is D: All of the above. Hospital-acquired infections can be caused by a variety of bacteria commonly found in healthcare settings. Staphylococcus aureus is a common cause of surgical site infections. Escherichia coli can cause urinary tract infections. Klebsiella pneumoniae is associated with pneumonia and bloodstream infections. Therefore, all three bacteria are frequently implicated in hospital-acquired infections due to their prevalence and ability to cause different types of infections in healthcare settings. Thus, the correct answer is D, as all of the listed bacteria are commonly associated with hospital-acquired infections.
Which of the following is a host-dependent bacterium?
- A. Mycoplasma
- B. Ureaplasma
- C. Rickettsia
- D. Micrococcus
Correct Answer: C
Rationale: The correct answer is C: Rickettsia. Rickettsia is a host-dependent bacterium because it requires living cells of a host organism to survive and replicate. This bacterium is an obligate intracellular pathogen, meaning it cannot grow outside of a host cell.
A: Mycoplasma and B: Ureaplasma are not host-dependent as they can grow and reproduce in cell-free environments due to possessing their own unique cell wall structures.
D: Micrococcus is a free-living bacterium that can survive and reproduce independently without relying on a host organism.