Nokea
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.
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Streptococcus pyogenes releases:
- A. Enterotoxin
- B. Streptolysin
- C. Staphylocoagulase
- D. None of the above
Correct Answer: B
Rationale: The correct answer is B: Streptolysin. Streptolysin is a toxin released by Streptococcus pyogenes that causes lysis of red blood cells and contributes to the pathogenicity of the bacteria. Enterotoxin (Choice A) is typically produced by Staphylococcus aureus, not Streptococcus pyogenes. Staphylocoagulase (Choice C) is an enzyme produced by Staphylococcus aureus to promote blood clot formation and is not associated with Streptococcus pyogenes. Therefore, the correct answer is B as Streptolysin is the toxin released by Streptococcus pyogenes.
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
Which bacterium is known as a common cause of hospital-acquired infections?
- A. Clostridium botulinum
- B. Staphylococcus aureus
- C. Treponema pallidum
- D. Mycobacterium leprae
Correct Answer: B
Rationale: The correct answer is B: Staphylococcus aureus. This bacterium is known as a common cause of hospital-acquired infections due to its ability to colonize the skin and mucous membranes of healthcare workers and patients. Staphylococcus aureus can cause various infections, including surgical site infections and bloodstream infections, in healthcare settings.
Rationale:
1. Clostridium botulinum is known for causing foodborne botulism, not hospital-acquired infections.
2. Treponema pallidum causes syphilis, which is primarily transmitted through sexual contact, not hospital settings.
3. Mycobacterium leprae causes leprosy, which is not commonly associated with hospital-acquired infections.
In summary, Staphylococcus aureus is the correct answer as it is a common cause of hospital-acquired infections due to its prevalence in healthcare environments, unlike the other choices which are not typically associated with hospital-acquired infections.
For shigella is true:
- A. They produce hydrogen sulfide
- B. They ferment lactose
- C. They are nonmotile
- D. All of them are mannitol positive
Correct Answer: C
Rationale: Step-by-step rationale:
1. Shigella is a nonmotile bacterium.
2. This lack of motility is a key characteristic used to differentiate it from other enteric bacteria.
3. Nonmotile nature of Shigella helps it to cause infections by invading the intestinal epithelial cells.
4. Therefore, choice C is correct as Shigella is indeed nonmotile.
Summary:
A: Incorrect - Shigella does not produce hydrogen sulfide.
B: Incorrect - Shigella does not ferment lactose.
D: Incorrect - Shigella is not mannitol positive.
Enzymes used in ELISA are those except:
- A. Î’-lactamase
- B. Alkaline phosphatase
- C. Horseradish peroxidase
- D. Î’- galactosidase
Correct Answer: A
Rationale: The correct answer is A: Β-lactamase. In ELISA, enzymes like alkaline phosphatase, horseradish peroxidase, and Β-galactosidase are commonly used as labels to detect the presence of specific molecules. Β-lactamase is not typically used in ELISA as it is an enzyme used to hydrolyze β-lactam antibiotics. Therefore, it does not serve the purpose of detecting specific molecules in ELISA. Alkaline phosphatase, horseradish peroxidase, and Β-galactosidase are preferred enzymes in ELISA due to their ability to produce a detectable signal when bound to specific molecules.