medical microbiology test bank

Correct Answer: C

Rationale: The correct answer is C: Endospore. Endospores are highly resistant structures formed by certain bacterial species to withstand harsh conditions like desiccation. They contain a tough outer layer that protects the bacterial DNA and other essential components. Capsules (choice A) provide protection against host immune responses but not specifically against desiccation. Flagella (choice B) are used for bacterial motility. Pili (choice D) are involved in bacterial adhesion but do not protect against desiccation. Therefore, endospores are the most suitable choice for protecting against desiccation.

Correct Answer: B

Rationale: Correct Answer: B - Plasmids are circular DNA molecules Rationale: 1. Plasmids are extrachromosomal DNA molecules found in bacteria. 2. Plasmids are typically circular in structure, not linear. 3. Circular plasmids are easily replicated and transferred between bacteria. 4. Plasmids can carry genes for antibiotic resistance, making option C incorrect. 5. Not all bacteria have plasmids, making option D incorrect. 6. While plasmids can provide benefits, they are not essential for bacterial survival, making option A incorrect.

Correct Answer: A

Rationale: The most probable diagnosis is Dermatotropic leishmaniasis. The roundish ulcers, lymph node enlargement, and presence of unicellular aflagellar organisms in discharge are characteristic of this parasitic infection transmitted by sandfly bites. Leishmania parasites cause skin lesions and lymphadenopathy. Toxoplasmosis (B) presents with flu-like symptoms, not ulcers. Scabies (C) causes intense itching and burrows, not ulcers. Trypanosomiasis (D) presents with fever, not ulcers. In this case, the symptoms align closely with Dermatotropic leishmaniasis, making it the most likely diagnosis.

Correct Answer: C

Rationale: The correct answer is C: Bacillus subtilis. Bacillus subtilis is known for its spore-forming ability, which is a survival mechanism to withstand harsh conditions. Spore formation allows the bacteria to become dormant and resistant to heat, chemicals, and radiation. Escherichia coli (A) is not known for spore formation. Staphylococcus aureus (B) does not form spores either. Listeria monocytogenes (D) is a pathogenic bacterium but does not typically form spores.

Correct Answer: B

Rationale: The correct answer is B because the AST reaction, or anti-streptolysin titer, is used in the diagnostic of post-streptococcal sequelae, such as rheumatic fever and glomerulonephritis. This test measures the level of antibodies produced by the body in response to Streptolysin O, a toxin produced by Group A Streptococcus bacteria. It helps in identifying if a patient has had a recent Streptococcus infection that could lead to these complications. A: Incorrect. The AST reaction does not require urine samples, but rather blood samples. C: Incorrect. The AST reaction specifically targets antibodies produced in response to Group A Streptococcus. D: Incorrect. The AST reaction does not directly identify isolated streptococci but rather measures the body's immune response to Streptolysin O.