Which of the following bacteria is known for causing dental caries (cavities)?

Correct Answer: A

Rationale: Step 1: Streptococcus mutans is known for its ability to produce acids that contribute to the demineralization of tooth enamel, leading to dental caries. Step 2: Streptococcus pneumoniae is a common cause of respiratory infections, not dental caries. Step 3: Bacillus anthracis causes anthrax, a serious bacterial infection, not dental caries. Step 4: Clostridium botulinum causes botulism, a severe form of food poisoning, not dental caries. Summary: Streptococcus mutans is the correct answer as it is specifically associated with causing dental caries, while the other choices are linked to different diseases.

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: A

Rationale: Step-by-step rationale: 1. IgG is the most abundant immunoglobin in a normal healthy adult due to its long half-life and diverse functions. 2. It plays a crucial role in immune response by neutralizing pathogens and enhancing phagocytosis. 3. IgA is mainly found in mucosal areas, IgE is involved in allergic reactions, and IgD's function is not fully understood. 4. Therefore, IgG is the correct answer as it is the predominant immunoglobin in circulation, providing broad immune protection.

Correct Answer: D

Rationale: The correct answer is D because there is specific prophylaxis available for influenza, such as the flu vaccine. Choice A is incorrect as influenza viruses are not spherical, they are typically pleomorphic. Choice B is incorrect because hemagglutinin and neuraminidase are indeed antigenically variable, contributing to the need for annual flu vaccines. Choice C is incorrect as the susceptibility of the population to influenza viruses can vary depending on factors such as immunity and vaccination status.

Correct Answer: B

Rationale: The correct answer is B: Pseudomonas aeruginosa. This bacterium is important for controlling air quality as it can degrade a wide range of organic compounds present in the air, helping to maintain a clean and healthy environment. Alpha and beta-hemolytic streptococci (Choice A) are not typically associated with air quality control. E. coli (Choice C) and Salmonella spp. (Choice D) are more commonly found in water and food sources, not air, making them incorrect choices for this question. Pseudomonas aeruginosa's ability to break down organic matter in the air makes it the most suitable option for maintaining sanitary air quality.