Nokea
An example of selective media is:
- A. McConkey agar
- B. Bordet Gengou agar
- C. Peptone water
- D. None of the above
Correct Answer: A
Rationale: The correct answer is A: McConkey agar. Selective media selectively inhibit the growth of certain organisms while allowing others to grow. McConkey agar contains crystal violet and bile salts that inhibit the growth of Gram-positive bacteria, making it selective for Gram-negative bacteria. Choices B and C are not selective media, as they do not specifically inhibit the growth of certain types of bacteria. Choice D is incorrect as McConkey agar is indeed an example of selective media.
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The causative agent of bacterial dysentery belongs to which of the following genera?
- A. Genus Shigella
- B. Genus Salmonella
- C. Genus Klebsiella
- D. None of the above
Correct Answer: A
Rationale: The correct answer is A: Genus Shigella. Shigella is known to be the causative agent of bacterial dysentery. It invades the intestinal lining, leading to symptoms like severe diarrhea and abdominal cramps. Salmonella (choice B) typically causes food poisoning, not dysentery. Klebsiella (choice C) is associated with pneumonia and urinary tract infections, not dysentery. "None of the above" (choice D) is incorrect as Shigella does belong to a specific genus responsible for bacterial dysentery.
The eukaryotes known for the presence of a macronucleus and a micronucleus are:
- A. algae
- B. fungi
- C. protozoans
- D. slime molds
Correct Answer: C
Rationale: The correct answer is C: protozoans. Protozoans are eukaryotic organisms that possess both a macronucleus, responsible for general cell functions, and a micronucleus, involved in genetic processes like reproduction. Algae (choice A) typically have a single nucleus, fungi (choice B) lack distinct macronucleus and micronucleus structures, and slime molds (choice D) do not have the same nucleus organization as protozoans. Thus, protozoans are the only group among the choices that exhibit the specific characteristics of having both a macronucleus and a micronucleus.
Widal test is used to diagnose
- A. Syphilis
- B. Typhoid fever
- C. AIDS
- D. Lyme disease
Correct Answer: B
Rationale: The Widal test is used to diagnose typhoid fever caused by the bacteria Salmonella typhi. The test detects antibodies produced in response to the bacteria. Positive results indicate a current or past infection with typhoid fever. Choice A (Syphilis) is incorrect as it is diagnosed using different tests like RPR or TPPA. Choice C (AIDS) is diagnosed with HIV tests like ELISA or Western blot. Choice D (Lyme disease) is diagnosed using tests like ELISA or Western blot specific for Borrelia burgdorferi.
Which one of the following is a normal skin flora?
- A. Streptococcus pyogenes
- B. Staphylococcus epidermidis
- C. Pseudomonas aeruginosa
- D. Acinetobacter baumannii
Correct Answer: B
Rationale: The correct answer is B: Staphylococcus epidermidis. This bacterium is a normal skin flora commonly found on human skin. It is part of the skin microbiota and helps protect against pathogenic organisms. Streptococcus pyogenes (A), Pseudomonas aeruginosa (C), and Acinetobacter baumannii (D) are not normal skin flora. Streptococcus pyogenes is a pathogenic bacterium causing various infections, Pseudomonas aeruginosa is an opportunistic pathogen commonly found in water and soil, and Acinetobacter baumannii is associated with healthcare-associated infections.
The specific binding of HIV to the CD4 surface molecules of the target cells is brought about by:
- A. Gp120
- B. Gp41
- C. Gp32
- D. Gp55
Correct Answer: A
Rationale: The correct answer is A: Gp120. Gp120 is a glycoprotein on the surface of the HIV virus that specifically binds to the CD4 receptor on target cells. This binding is essential for the virus to enter the host cell and initiate the infection process. Gp41 is another glycoprotein on the virus that helps with membrane fusion, not binding to CD4. Gp32 and Gp55 are not involved in the specific binding of HIV to CD4 molecules. So, A is correct as it directly plays a key role in the initial attachment of HIV to target cells.