Nokea
Tuberculosis can be treated by means of combined chemotherapy that includes substances with different mechanisms of action. What antituberculous medication inhibits transcription of RNA into DNA in mycobacteria?
- A. Rifampicin
- B. Isoniazid
- C. Streptomycin
- D. Ethionamide
Correct Answer: A
Rationale: Rifampicin is the correct answer because it inhibits RNA transcription in mycobacteria by binding to the bacterial RNA polymerase. This prevents the synthesis of RNA, leading to the inhibition of protein production essential for bacterial growth.
Isoniazid inhibits mycolic acid synthesis, Streptomycin inhibits protein synthesis, and Ethionamide disrupts mycolic acid synthesis. These mechanisms are different from inhibiting RNA transcription, making them incorrect choices.
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The Gram stain is used to differentiate bacteria based on:
- A. Cell shape
- B. Cell wall structure
- C. Flagella composition
- D. Nutrient requirements
Correct Answer: B
Rationale: The Gram stain differentiates bacteria based on cell wall structure. It classifies bacteria into Gram-positive (purple) and Gram-negative (pink) based on the presence of peptidoglycan in the cell wall. This method helps in identifying the bacterial species and determining appropriate treatment. Option A (Cell shape) is incorrect because the Gram stain focuses on cell wall composition, not cell shape. Option C (Flagella composition) is incorrect as the Gram stain does not assess flagella. Option D (Nutrient requirements) is incorrect as it does not relate to the purpose of the Gram stain.
The First-line tuberculosis drugs include:
- A. Isoniazid and rifampicin
- B. Penicillin and erythromycin
- C. Trimethoprim and third generation cephalosporins
- D. All the listed above can be used depending on their resistance profile
Correct Answer: A
Rationale: The correct answer is A: Isoniazid and rifampicin. These drugs are considered first-line treatment for tuberculosis due to their high efficacy and low toxicity. Isoniazid targets the cell wall of the tuberculosis bacteria, while rifampicin inhibits RNA synthesis. They are recommended by WHO as the first choice for treating tuberculosis.
Choice B (Penicillin and erythromycin) is incorrect because these antibiotics are not effective against tuberculosis bacteria.
Choice C (Trimethoprim and third generation cephalosporins) is incorrect because they are not considered first-line drugs for tuberculosis treatment.
Choice D (All the listed above can be used depending on their resistance profile) is incorrect because only isoniazid and rifampicin are universally recognized as first-line drugs for tuberculosis regardless of resistance profile.
The Staphylococcus aureus toxin, which can cause scalded skin syndrome (SSS), is:
- A. hemolysis
- B. enterotoxin
- C. leucocidin
- D. epidermolytic toxin
Correct Answer: D
Rationale: The correct answer is D: epidermolytic toxin. This toxin specifically targets the epidermis, leading to exfoliation seen in scalded skin syndrome (SSS). Hemolysis (A) refers to the destruction of red blood cells, not relevant to SSS. Enterotoxins (B) cause food poisoning, not SSS. Leucocidins (C) target white blood cells, not pertinent to SSS. Therefore, the epidermolytic toxin (D) is the correct choice for causing SSS.
A centrifugate of urine sample obtained from patient with suspected renal tuberculosis was used to make a slide mount for microscopy. What method should be used to stain the slide and detect the causative agent?
- A. Zielh-Neelsen stain
- B. Loeffler stain
- C. Gram stain
- D. Aujeszky stain
Correct Answer: A
Rationale: The correct answer is A: Zielh-Neelsen stain. This stain is specifically used to detect acid-fast bacteria like Mycobacterium tuberculosis, the causative agent of renal tuberculosis. The staining process involves using carbol fuchsin to penetrate the mycolic acid layer of the bacterial cell wall, making it resistant to decolorization with acid-alcohol. This allows the red stained bacteria to be visualized under a microscope. Loeffler stain (B) is used for staining bacteria like diphtheria bacilli, Gram stain (C) is used for bacterial classification based on cell wall properties, and Aujeszky stain (D) is not a recognized staining method for detecting acid-fast bacteria.
Precipitation reaction can be converted into agglutination reaction by coating soluble antigen onto
- A. Bentonite (clay) particles
- B. RBCs
- C. Latex particles
- D. All of these
Correct Answer: D
Rationale: The correct answer is D: All of these. Coating soluble antigen onto Bentonite particles, RBCs, or Latex particles can convert a precipitation reaction into an agglutination reaction. This is because soluble antigens bind to their specific antibodies, causing the particles to clump together, visible as agglutination. Bentonite particles, RBCs, and Latex particles all provide surfaces for the antigen-antibody interaction to occur, leading to agglutination. Therefore, all of these options are correct for converting precipitation reactions to agglutination reactions.