Which of the following bacteria produce a neurotoxin that affects the nervous system?

Correct Answer: C

Rationale: Rationale: Both Clostridium botulinum and Clostridium tetani produce neurotoxins. Botulinum toxin affects the nervous system by blocking neurotransmitter release, causing paralysis. Tetanus toxin affects the nervous system by interfering with neurotransmitter release, leading to muscle stiffness and spasms. Therefore, Choice C is correct. Choices A and B alone are incorrect because they only mention one of the bacteria that produces a neurotoxin. Choice D is incorrect because both bacteria mentioned in Choices A and B produce neurotoxins.

Correct Answer: B

Rationale: The optochin sensitivity test is used to differentiate Pneumococcal (Streptococcus pneumoniae) from other streptococci. Optochin sensitivity is a characteristic feature of Pneumococcal, as it inhibits its growth. The test involves placing optochin discs on a culture plate and observing the zone of inhibition around the disc for Pneumococcal. Neisseria gonorrhoeae, Staphylococci, and Group A streptococci do not exhibit optochin sensitivity, making them incorrect choices. In summary, the optochin sensitivity test is specific to Pneumococcal, making choice B the correct answer.

Correct Answer: A

Rationale: The correct answer is A: Streptomycin. Streptomycin is an aminoglycoside antibiotic used to treat tuberculosis that can cause hearing loss as a side effect. It is known to damage the cochlear and vestibular organs in the inner ear. The other choices, B: Isoniazid, C: Rifampicin, and D: Ethionamide, are not associated with causing hearing deterioration as a side effect. Isoniazid can rarely cause peripheral neuropathy, Rifampicin can lead to hepatotoxicity, and Ethionamide may cause gastrointestinal disturbances, but none of these drugs are known to specifically cause hearing loss.

Correct Answer: A

Rationale: The correct answer is A: Transformation. During transformation, bacteria take up foreign DNA from the environment and incorporate it into their own genetic material. This process allows for genetic diversity and adaptation. Transduction (B) involves transfer of DNA via a virus, conjugation (C) involves direct transfer of DNA between bacterial cells, and binary fission (D) is a form of asexual reproduction in bacteria. Transformation is the only process specifically related to bacteria taking up foreign DNA.

Correct Answer: A

Rationale: The correct answer is A: Entamoeba gingivalis. Firstly, it is important to note that Entamoeba gingivalis is commonly found in the oral cavity, specifically in carious cavities. Secondly, Entamoeba gingivalis belongs to the Sarcodina class, which is characterized by their amoeboid movement using pseudopods. This protozoa is associated with oral health issues, particularly in individuals with poor oral hygiene. Now, let's analyze why the other choices are incorrect: B: Entamoeba histolutica is known for causing amoebic dysentery, not commonly associated with oral cavities. C: Entamoeba coli is typically found in the human large intestine, not in oral cavities. D: Amoeba proteus is a free-living amoeba commonly used in laboratory studies and not typically associated with oral cavity infections.

Correct Answer: C

Rationale: The correct answer is C because both Clostridium botulinum and Bacillus anthracis are capable of forming spores to survive in extreme conditions. Clostridium botulinum is known for causing botulism and produces highly heat-resistant spores, while Bacillus anthracis is the causative agent of anthrax and also forms spores. Choice A is incorrect because only Clostridium botulinum is mentioned, not Bacillus anthracis. Choice B is incorrect because only Bacillus anthracis is mentioned, not Clostridium botulinum. Choice D is incorrect as it states that none of the bacteria can form spores, which is false based on the characteristics of Clostridium botulinum and Bacillus anthracis.

Correct Answer: C

Rationale: The correct answer is C because bacteriocins are substances with protein nature, not polysaccharides. Bacteriocins are antimicrobial peptides that kill bacterial cells, mainly those of closely related species or other strains of the same species. Polysaccharides are not typically involved in bacteriocin activity. Therefore, option C is false. Options A, B, and D are true statements supported by the nature and function of bacteriocins.

Correct Answer: B

Rationale: The correct answer is B: Isolation on cell cultures. This method is the gold standard for routine mumps diagnosis as it involves isolating the virus in cell cultures to confirm the presence of the mumps virus. PCR (choice A) is used for detecting viral RNA, not for routine diagnosis. ELISA (choice C) detects antibodies, not the virus itself. Immunofluorescence method (choice D) is used for visualizing viral antigens but is not as reliable as isolating the virus in cell cultures for diagnosis.

Correct Answer: A

Rationale: The correct answer is A because a soft chancre is a type of sexually transmitted infection caused by the bacterium Haemophilus ducreyi. It presents as a painless ulcer on the genitals. The other choices are incorrect. B is incorrect because STIs can enter the body through various routes, not only the urogenital tract mucosa. C is incorrect because immunity to syphilis is not lifelong; reinfection is possible. D is incorrect because STIs can occur in any country regardless of social status or hygiene levels.