Which of the following statements is NOT true about influenza viruses?

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: C

Rationale: The correct answer is C because Rickettsia requires living cells for growth and replication. Chick embryos, cell cultures, and lab animals provide a suitable environment for Rickettsia isolation. Skin-allergy tests (A) and serological methods for proving antibodies (B) are not directly used for isolating Rickettsia as they do not support the growth of the bacteria. "None of the above" (D) is incorrect as option C involves the appropriate methods for isolating Rickettsia.

Correct Answer: A

Rationale: Step-by-step rationale: 1. Gram-positive rods with terminal spores suggest Clostridium genus. 2. Terminal spores are characteristic of Clostridium perfringens. 3. C. perfringens is known to cause wound infections. 4. Therefore, the most likely causative agent is Clostridium perfringens. Summary: A: Clostridium perfringens is correct due to its characteristic features and association with wound infections. B: Bacillus anthracis does not typically form terminal spores. C: Clostridium tetani causes tetanus, not wound infections. D: Bacillus cereus does not produce terminal spores like Clostridium perfringens.

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: B

Rationale: The correct answer is B because sterilization is the process of completely destroying all microorganisms, including resistant forms like spores, ensuring no viable organisms remain. This is crucial for ensuring complete elimination of potential pathogens. Choice A is incorrect because sterilization should eliminate all microorganisms, including spores. Choice C is incorrect as it describes disinfection, not sterilization. Choice D is incorrect because sterilization aims to eradicate all microorganisms, not leave any viable ones behind.

Correct Answer: A

Rationale: The correct answer is A: Neutralization. In this scenario, the antibotulinic serum of types A, B, and E were introduced to neutralize the botulinum toxin in the test specimen. The serological reaction applied here involves the neutralization of the toxin by the specific antibodies present in the serum. This process prevents the toxin from causing harm to the mice. Summary of other choices: B: Precipitation - This involves the formation of insoluble complexes between antigen and antibody, not the specific neutralization seen in this case. C: Complement binding - This involves activation of the complement system leading to cell lysis, not the direct neutralization of toxin. D: Double immune diffusion - This technique is used to determine the presence of specific antibodies or antigens based on their diffusion patterns, not the neutralization of toxin as seen in this scenario.

Correct Answer: A

Rationale: The correct answer is A: Clostridium botulinum. Clostridium botulinum produces the botulinum toxin, which causes botulism. This bacteria thrives in anaerobic environments and can contaminate improperly canned foods. Clostridium tetani causes tetanus, not botulism. Staphylococcus aureus produces enterotoxins causing food poisoning, not botulism. Escherichia coli can cause food poisoning through various toxins, but not botulism. Therefore, the correct choice is Clostridium botulinum as it specifically produces the botulinum toxin responsible for botulism.

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: A

Rationale: The most probable diagnosis is A: Candidous cheilitis. Candidous cheilitis is a fungal infection caused by Candida species. In this case, the presence of mycelium on the plaques indicates a fungal infection. The symptoms of pain, burning, and grey plaques that can be easily removed leaving hyperemia are typical for Candidous cheilitis. Choice B (Exfoliative cheilitis) is characterized by scaling and peeling of the lips, not plaques with mycelium. Choice C (Leukoplakia) is a precancerous condition causing white plaques that cannot be easily removed. Choice D (Contactant allergic cheilitis) is an allergic reaction causing inflammation, not fungal plaques.