Which bacterium is known for producing an exotoxin that causes severe diarrhea?

Correct Answer: C

Rationale: Rationale: 1. Vibrio cholerae produces cholera toxin causing severe diarrhea. 2. Clostridium tetani causes tetanus, not diarrhea. 3. Clostridium botulinum causes botulism, not diarrhea. 4. Shigella dysenteriae causes dysentery, not typical diarrhea. Summary: A: Incorrect, causes tetanus. B: Incorrect, causes botulism. C: Correct, produces cholera toxin causing severe diarrhea. D: Incorrect, causes dysentery.

Correct Answer: C

Rationale: Rationale: C is the correct answer because antibodies formed against Mycobacterium tuberculosis are not protective. They do not efficiently clear the infection due to the bacterium's ability to evade the immune response by residing intracellularly in macrophages. Antibodies play a minimal role in controlling tuberculosis compared to cell-mediated immunity. Summary: A is incorrect because Mycobacterium tuberculosis does contain mycolic acid in its cell wall. B is incorrect because the pathogen can indeed live intracellularly in macrophages. D is incorrect as C is the correct answer.

Correct Answer: B

Rationale: The correct answer is B: Mycobacterium leprae. This microorganism can only be cultured in the footpads of mice or a species of armadillo due to its specific growth requirements. Mycobacterium tuberculosis (choice A) can be cultured in various culture media in the laboratory. Neisseria gonorrhoeae (choice C) can be cultured on selective media like Thayer-Martin agar. Mycoplasma (choice D) can be cultured in cell cultures or specialized media. Therefore, the unique growth pattern of Mycobacterium leprae makes it the correct answer.

Correct Answer: A

Rationale: The correct answer is A: Streptococcus pyogenes. This bacterium fits all the given characteristics: Gram-positive cocci arranged in chains, catalase-negative, and beta-hemolytic on blood agar. Streptococcus pyogenes is known for causing skin and soft tissue infections. Staphylococcus aureus (B) is catalase-positive and typically forms clusters, not chains. Enterococcus faecalis (C) is catalase-negative but not beta-hemolytic. Micrococcus luteus (D) is catalase-positive and not typically associated with wound infections.

Correct Answer: A

Rationale: The correct answer is A: Staphylococcus aureus and hemolytic streptococcus. These microorganisms are commonly found in high concentrations during sanitary and bacteriological examination of air in a drugstore due to their prevalence in the environment. Staphylococcus aureus and hemolytic streptococcus are known to be significant pathogens that can cause various infections in humans. Rationale: 1. Staphylococcus aureus and hemolytic streptococcus are common pathogens found in the environment and can easily contaminate air in enclosed spaces like a drugstore. 2. Both microorganisms are considered to be of sanitary significance as they can cause infections and are indicators of poor hygiene and sanitation. 3. Diphtheritic and tuberculous bacilli (Choice B) are not typically associated with air contamination in a drugstore setting. 4. Colibacilli and blue pus bacilli (Choice C) are more commonly found in fecal

Correct Answer: A

Rationale: The correct answer is A: Streptococcus pneumoniae. This bacterium is the most likely causative agent based on the description of Gram-positive cocci in pairs with a capsule. S. pneumoniae is known for its characteristic morphology and the presence of a capsule, which helps in evading the immune system. It commonly causes pneumonia, especially in patients with a productive cough and fever. Incorrect choices: B: Klebsiella pneumoniae typically presents with a mucoid capsule and is associated with pneumonia in immunocompromised individuals. C: Neisseria meningitidis is a Gram-negative diplococcus and is more commonly associated with meningitis and septicemia. D: Staphylococcus aureus is a Gram-positive cocci, but it does not typically present in pairs with a capsule and is more commonly associated with skin and soft tissue infections.

Correct Answer: C

Rationale: The correct descending order of taxonomic categories is domain, kingdom, phylum, class, order, family, genus, species. This hierarchical classification system helps organize and categorize living organisms based on their shared characteristics and evolutionary relationships. Explanation: - Domain is the broadest category, representing the highest level of classification. - Kingdom further divides organisms into major groups based on similar characteristics. - Phylum, class, order, family, and genus successively narrow down the classification based on more specific shared characteristics. - Species is the most specific category, representing individual organisms capable of interbreeding. Summary of other choices: A: Incorrect as it has the incorrect order of phylum, kingdom, and division. B: Incorrect as it has the incorrect order of family and species. D: Incorrect as it has the incorrect order of domain, kingdom, and class.

Correct Answer: B

Rationale: The correct answer is B: Vibrio cholerae. Cholera is caused by Vibrio cholerae, a bacterium that produces a toxin leading to severe diarrhea and dehydration. Clostridium botulinum (A) causes botulism, Salmonella enterica (C) causes salmonellosis, and Escherichia coli (D) can cause various illnesses but not cholera. Vibrio cholerae is the only bacteria specifically known for causing cholera.

Correct Answer: D

Rationale: The correct answer is D because viruses are sensitive to interferon, a natural defense mechanism of the body against viral infections. Interferon helps to inhibit viral replication. A: Viruses are cell-free infectious particles, not living systems. B: Viruses are obligate intracellular parasites as they require host cells to replicate. C: Viruses can have either DNA or RNA as genetic material, which is a characteristic feature.