free microbiology test bank questions pdf

Correct Answer: D

Rationale: The correct answer is D: All of these. HBV, HCV, and HDV can all lead to chronic carrier states due to their ability to establish persistent infections in the liver. HBV can result in chronic hepatitis, cirrhosis, and even liver cancer. HCV can also lead to chronic hepatitis and liver damage. HDV is a defective virus that requires HBV for replication and can worsen the outcome of HBV infection, potentially leading to chronic liver disease. Therefore, all three viruses have the potential to cause chronic carrier states.

Correct Answer: B

Rationale: The correct answer is B: Mycobacterium tuberculosis. Mycobacterium tuberculosis is the causative agent of tuberculosis, as it specifically infects the lungs and can spread to other parts of the body. Mycobacterium leprae (Choice A) causes leprosy, not tuberculosis. Bacillus anthracis (Choice C) causes anthrax, not tuberculosis. Staphylococcus aureus (Choice D) is a common bacterium known for causing skin infections, not tuberculosis. Therefore, Mycobacterium tuberculosis is the correct answer for the causative agent of tuberculosis.

Correct Answer: A

Rationale: The correct serological test for diagnosing toxoplasmosis is the Complement Binding Assay (A) because it detects antibodies specific to the Toxoplasma gondii parasite. This test is highly sensitive and specific for toxoplasmosis. Choice B, Precipitation test, is not used for toxoplasmosis diagnosis but rather for other diseases like syphilis. Choice C, Neutralization test, is not specific for toxoplasmosis and is used for other types of infections. Choice D, Widal's test, is used for diagnosing typhoid fever and is not relevant for toxoplasmosis. In summary, the correct answer (A) is specific to toxoplasmosis, while the other choices are used for different diseases and are not suitable for diagnosing toxoplasmosis.

Correct Answer: D

Rationale: The correct answer is D. Isoniazid inhibits pyridoxal phosphate synthesis, which is the active form of vitamin B6. Pyridoxal phosphate is essential for various enzymatic reactions, including neurotransmitter synthesis and myelin formation. Therefore, isoniazid-induced pyridoxal phosphate deficiency can lead to neurological symptoms like polyneuritis, paresthesia, memory disorders, and convulsions. A: Disruption of cell membrane synthesis - This is not the mechanism of isoniazid side-effects. B: Inhibition of protein synthesis - Isoniazid does not directly inhibit protein synthesis. C: Inhibition of RNA-synthesis - Isoniazid does not inhibit RNA synthesis; it affects vitamin B6 metabolism.

Correct Answer: A

Rationale: The correct answer is A: mRNA. mRNA carries the genetic code from the DNA in the cell nucleus to the ribosomes in the cytoplasm, where protein synthesis occurs. It serves as a template for protein synthesis by specifying the order of amino acids. tRNA (choice B) brings amino acids to the ribosome during protein synthesis. rRNA (choice C) is a structural component of ribosomes. snRNA (choice D) is involved in RNA processing and splicing, not protein synthesis. Therefore, choice A is correct as it directly carries the genetic code for protein synthesis.