Which of the following bacteria produces a neurotoxin that causes botulism?

Correct Answer: A

Rationale: The correct answer is A: Clostridium botulinum. Clostridium botulinum produces the neurotoxin that causes botulism. This bacterium thrives in anaerobic conditions and contaminated food. The neurotoxin blocks acetylcholine release at the neuromuscular junction, leading to muscle paralysis. Choices B, C, and D are incorrect because Clostridium tetani causes tetanus, Escherichia coli can cause food poisoning but not botulism, and Staphylococcus aureus produces enterotoxins causing food poisoning, not botulism.

Correct Answer: D

Rationale: Step 1: Mantoux test measures cell-mediated immunity response to tuberculosis. Step 2: A negative result means no significant immune response to TB antigens. Step 3: Option A is incorrect, as it refers to antitoxic immunity, not cell immunity. Step 4: Option B is incorrect, as it mentions antibodies, not cell-mediated immunity. Step 5: Option C is incorrect, as it states absence of antibodies, not cell immunity. Step 6: Option D is correct as it directly correlates with the purpose of Mantoux test.

Correct Answer: B

Rationale: Answer B, Infectious mononucleosis, is not caused by enteroviruses. Infectious mononucleosis is primarily caused by the Epstein-Barr virus, a member of the herpesvirus family, not by enteroviruses. Enteroviruses are known to cause diseases such as myocarditis, herpangina, and Boston exanthema. Therefore, B is the correct answer. Myocarditis, herpangina, and Boston exanthema can all be caused by enteroviruses, making choices A, C, and D incorrect, respectively.

Correct Answer: A

Rationale: The correct answer is A: Pseudomonas aeruginosa. Pseudomonas aeruginosa is a gram-negative bacterium known for its green-blue pigmentation and sweet, fruity odor. The large colorless mucous colonies that develop green-blue pigmentation and honey or jasmine smell point towards Pseudomonas aeruginosa. The bacterioscopy revealing gram-negative lophotrichea further supports this identification. Proteus vulgaris and Klebsiella osaenae do not typically exhibit the described characteristics. Streptomyces griseus is a soil bacterium known for its antibiotic production and is not commonly associated with wound infections.

Correct Answer: A

Rationale: The correct answer is A: Clostridium botulinum. Clostridium botulinum produces the neurotoxin that causes botulism. This bacterium thrives in anaerobic conditions and contaminated food. The neurotoxin blocks acetylcholine release at the neuromuscular junction, leading to muscle paralysis. Choices B, C, and D are incorrect because Clostridium tetani causes tetanus, Escherichia coli can cause food poisoning but not botulism, and Staphylococcus aureus produces enterotoxins causing food poisoning, not botulism.

Correct Answer: B

Rationale: Rationale: 1. Streptococcus pyogenes is the causative agent of strep throat. 2. If untreated, strep throat can lead to rheumatic fever. 3. Rheumatic fever is an autoimmune complication of streptococcal infections. 4. E. coli, S. epidermidis, and S. aureus are not typically associated with rheumatic fever.

Correct Answer: A

Rationale: The correct answer is A: Oxidation. Phase I reactions in biotransformation involve introducing or unmasking functional groups through oxidation, reduction, or hydrolysis. Oxidation reactions typically involve the addition of an oxygen atom or removal of hydrogen atoms, making them common phase I reactions. In this process, enzymes like cytochrome P450 play a crucial role in catalyzing the oxidation reactions. Conjugation (B), acetylation (C), and glucuronidation (D) are all examples of phase II reactions, which involve the conjugation of the drug or metabolite with endogenous compounds to increase water solubility for excretion. These reactions typically follow phase I reactions and are not classified as phase I reactions in biotransformation.

Correct Answer: C

Rationale: Toxoplasma gondii is a protozoan parasite known to cause toxoplasmosis. It belongs to the group of eukaryotic organisms called protozoans because it is a single-celled organism with complex cellular structures. Protozoans are characterized by their ability to move and perform essential functions independently. Algae (choice A) are photosynthetic eukaryotic organisms, fungi (choice B) are non-photosynthetic eukaryotes that include molds and yeasts, and helminths (choice D) are multicellular parasitic worms. Therefore, the correct answer is C because Toxoplasma gondii is a protozoan parasite.

Correct Answer: C

Rationale: The correct answer is C: Bacterial adhesion to the surface of the host cells, conjugation. Villi and cilia on the cell surface of pathogenic bacteria help in bacterial adhesion to host cells, facilitating the process of infection. Conjugation is the transfer of genetic material between bacterial cells, which can be aided by these structures. The other choices are incorrect because RNA exchange between cells (A) is typically facilitated by different structures like pili, inhibition of complement activity (B) is not related to the function of villi and cilia, and resistance to antibody opsonization (D) is usually achieved through other mechanisms such as capsule formation.