Which of the following media is the most selective for Vibrio cholerae?

Correct Answer: D

Rationale: The correct answer is D: TCBS. Thiosulfate-citrate-bile salts-sucrose (TCBS) agar is the most selective for Vibrio cholerae due to its high salt content, bile salts, and sucrose. Vibrio cholerae can grow well in alkaline conditions, which are provided by TCBS agar. MacConkey's agar (A) is selective for gram-negative bacteria, but not specifically for Vibrio cholerae. Chocolate agar (B) is a non-selective medium suitable for fastidious organisms. SS agar (C) is selective for Salmonella and Shigella species, not Vibrio cholerae.

Correct Answer: A

Rationale: The correct answer is A: Mycobacterium tuberculosis. This bacteria is responsible for causing tuberculosis because it is the specific pathogen known to infect the lungs and other parts of the body, leading to the disease. Mycobacterium tuberculosis has unique cell wall components that allow it to evade the immune system and survive in the host. Neisseria meningitidis (B) causes meningitis, not tuberculosis. Salmonella enterica (C) causes food poisoning, not tuberculosis. Streptococcus pneumoniae (D) causes pneumonia, not tuberculosis. Therefore, the correct answer is A based on the specific characteristics and pathogenicity of Mycobacterium tuberculosis.

Correct Answer: C

Rationale: The correct answer is C because the case specifically mentions "enteropathogenic bacteria and viruses," indicating a focus on these specific microorganisms. Choice A is too broad and includes all bacteria, which is not specified in the case. Choice B mentions opportunistic pathogenic bacteria, which are not necessarily relevant to the case. Choice D specifies colibacilli, which may or may not be relevant to the case, but it is not as specific as choice C which clearly matches the information provided in the case.

Correct Answer: B

Rationale: The correct answer is B because endotoxins are part of the outer membrane of gram-negative bacteria. When these bacteria undergo cell lysis, the endotoxins are released, causing harmful effects. This process does not occur during bacterial replication (choice A), antibody production (choice C), or formation of spores (choice D). Bacterial replication involves the creation of new bacterial cells, not the release of endotoxins. Antibody production is the immune response to pathogens, not the direct cause of endotoxin release. Spores are dormant structures formed by some bacteria, which are not directly related to the release of endotoxins.

Correct Answer: A

Rationale: The correct answer is A: Staphylococcus epidermidis. The presence of Gram-positive cocci in clusters indicates a staphylococcal species. The fact that the bacteria are catalase-positive and coagulase-negative further narrow it down to Staphylococcus epidermidis, as this species fits all the given characteristics. - Choice B, Staphylococcus aureus, is coagulase-positive. - Choice C, Streptococcus pyogenes, is a streptococcal species, not staphylococcal. - Choice D, Enterococcus faecalis, is a Gram-positive cocci but is catalase-negative and not typically found in clusters.

Correct Answer: A

Rationale: The correct answer is A: Bordetella pertussis. This bacterium causes whooping cough by attaching to the respiratory tract and releasing toxins that lead to severe coughing fits. Clostridium tetani causes tetanus, not whooping cough. Haemophilus influenzae can cause respiratory infections but not specifically whooping cough. Staphylococcus aureus is known for causing skin infections and not respiratory diseases like whooping cough. Therefore, the presence of Bordetella pertussis and its specific mechanism of causing whooping cough makes it the correct answer.

Correct Answer: A

Rationale: The correct answer is A: Anthrax. Anthrax is caused by the bacterium Bacillus anthracis, which can form spores that are highly resistant and can survive in the soil for long periods. These spores can remain dormant until they come into contact with a susceptible host, leading to infection. Diphtheria, viral hepatitis, and pertussis are caused by different types of pathogens (bacteria and viruses) that do not have the same ability to persist in soil as anthrax spores. Therefore, the causative agents of these diseases are less likely to exist in the soil for extended periods compared to anthrax spores.

Correct Answer: A

Rationale: The correct answer is A: Pertussis toxoid. This is because pertussis toxoid is a component of the pertussis vaccine, which provides specific prophylaxis against pertussis by stimulating the immune system to produce antibodies against the bacteria causing the disease. Choice B, killed vaccine, is incorrect as it does not specify pertussis toxoid. Choice C, wide-spectrum antibiotics, is incorrect as antibiotics are used for treatment, not prophylaxis. Choice D, None of the above, is incorrect as pertussis toxoid is specifically used for prophylaxis of pertussis.

Correct Answer: B

Rationale: The correct answer is B: Humoral immunity. Humoral immunity involves the production of antibodies by B cells that can bind to antigens on viruses, leading to their agglutination. This process prevents the spread of the virus in the body. Passive immunity (A) involves receiving pre-formed antibodies, not the production of antibodies. Cell-mediated immunity (C) involves the activation of T cells, not the direct agglutination of viruses. Non-specific immunity (D) refers to general defense mechanisms like inflammation and fever, not targeted agglutination of viruses.