Which of the following bacteria is associated with the disease known as whooping cough?

Correct Answer: A

Rationale: 1. Bordetella pertussis causes whooping cough. 2. It secretes toxins that damage the respiratory tract. 3. Symptoms include severe coughing fits and the characteristic "whoop" sound. 4. Clostridium tetani causes tetanus, not whooping cough. 5. Haemophilus influenzae causes various infections, not whooping cough. 6. Staphylococcus aureus causes skin infections, not whooping cough.

Correct Answer: B

Rationale: The correct answer is B: Absence of hemagglutination. In the reaction inhibition of hemagglutination, specific antibodies bind to antigens on red blood cells, preventing their agglutination. This results in the absence of visible clumping of red blood cells, which is known as hemagglutination. Therefore, the presence of specific antibodies is visualized by the absence of hemagglutination. Incorrect Choices: A: Absence of hemolysis - Hemolysis refers to the rupture of red blood cells, which is not relevant in the context of hemagglutination. C: Presence of hemagglutination - This is the opposite of what is expected when specific antibodies are present and inhibiting hemagglutination. D: Presence of hemolysis - Again, hemolysis is not directly related to the inhibition of hemagglutination by specific antibodies.

Correct Answer: A

Rationale: The correct answer is A: Logarithmic phase. During this phase, bacteria multiply exponentially due to abundant nutrients and favorable conditions. The growth is rapid and follows a geometric progression. In contrast, the Death phase (choice B) occurs when nutrients are depleted, leading to a decline in bacterial numbers. The Stationary phase (choice C) is when growth equals death rates, resulting in a stable population size. Choice D is incorrect because the Logarithmic phase accurately describes the exponential growth pattern of bacteria in artificial media.

Correct Answer: D

Rationale: The correct answer is D (4) because biosafety levels range from 1 to 4, each corresponding to the level of containment required when handling different types of organisms. BSL-1 is for low-risk agents, while BSL-4 is for dangerous pathogens. Choice A (1) is incorrect as there are multiple levels, not just one. Choice B (2) and C (3) are incorrect as they do not account for all the levels of biosafety required for handling various organisms. Therefore, D is the correct answer as it encompasses the full range of biosafety levels.

Correct Answer: A

Rationale: The correct answer is A: Clostridium perfringens. This bacterium fits all the characteristics mentioned: Gram-positive rods with spore formation, motile, and gas production in nutrient broth. Clostridium perfringens is known to cause gas gangrene, which aligns with the gas production in nutrient broth. Bacillus anthracis (B) causes anthrax and does not typically produce gas. Clostridium tetani (C) causes tetanus and does not form spores that are motile. Bacillus cereus (D) is a common cause of food poisoning and does not cause gas gangrene.

Correct Answer: C

Rationale: The correct answer is C: Rickettsia. Rickettsia is a host-dependent bacterium because it requires living cells of a host organism to survive and replicate. This bacterium is an obligate intracellular pathogen, meaning it cannot grow outside of a host cell. A: Mycoplasma and B: Ureaplasma are not host-dependent as they can grow and reproduce in cell-free environments due to possessing their own unique cell wall structures. D: Micrococcus is a free-living bacterium that can survive and reproduce independently without relying on a host organism.

Correct Answer: B

Rationale: The correct answer is B: Reverse transcriptase and protease. Reverse transcriptase converts viral RNA into DNA, a crucial step in viral replication. Protease is responsible for cleaving viral polyproteins into functional proteins. Targeting both enzymes disrupts viral replication. Choice A is incorrect as integrase is not a main target in current therapy. Choice C is incorrect because protease is targeted along with reverse transcriptase, not integrase. Choice D is incorrect as targeting viral glycoproteins is not a main strategy in anti-HIV therapy.

Correct Answer: C

Rationale: The pertussis toxin inhibits the adenylate cyclase-mediated conversion of ATP to cyclic AMP, leading to decreased levels of cyclic AMP in the cell. This disrupts important cellular signaling pathways, affecting immune response and causing symptoms of pertussis. Choices A, B, and D are incorrect because the pertussis toxin does not directly affect protein synthesis, provoke overproduction of mucus in tracheal cells, or provoke release of electrolytes.

Correct Answer: A

Rationale: The correct answer is A: Vibrio cholerae. This bacterium is the likely causative agent because it is known to cause severe diarrhea, and it is characterized by its motile, comma-shaped Gram-negative rods. Vibrio cholerae produces cholera toxin, leading to profuse watery diarrhea. Shigella dysenteriae causes dysentery with bloody diarrhea, Salmonella typhi causes typhoid fever, and Escherichia coli can cause various types of diarrhea but typically does not have a comma shape.