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Which bacteria produces an enterotoxin that causes diarrhea?
- A. Vibrio cholerae
- B. Clostridium botulinum
- C. Escherichia coli
- D. Streptococcus pneumoniae
Correct Answer: A
Rationale: The correct answer is A: Vibrio cholerae. This bacterium produces the cholera toxin, an enterotoxin that causes profuse watery diarrhea by disrupting the normal function of the intestines. Vibrio cholerae is specifically known for causing cholera, a severe diarrheal disease. Clostridium botulinum (B) produces botulinum toxin, causing botulism (paralysis, not diarrhea). Escherichia coli (C) can produce enterotoxins, but the question specifies a specific enterotoxin causing diarrhea, which is not a characteristic of all strains of E. coli. Streptococcus pneumoniae (D) is a common cause of respiratory infections but does not produce an enterotoxin causing diarrhea.
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Typhoid fever is caused by the bacterium:
- A. Escherichia coli
- B. Salmonella enterica
- C. Shigella flexneri
- D. Staphylococcus aureus
Correct Answer: B
Rationale: The correct answer is B: Salmonella enterica. Typhoid fever is caused by the bacterium Salmonella enterica serotype Typhi. This specific strain of Salmonella is responsible for typhoid fever, a serious illness characterized by high fever, abdominal pain, and diarrhea. Escherichia coli (choice A) is not the causative agent of typhoid fever. Shigella flexneri (choice C) causes bacillary dysentery, not typhoid fever. Staphylococcus aureus (choice D) can cause food poisoning but is not associated with typhoid fever.
What would be the conclusion?
- A. The water is safe for consumption
- B. The water quality is doubtful
- C. The water quality is extremely doubtful
- D. The water is polluted
Correct Answer: B
Rationale: Step-by-step rationale for choice B being correct:
1. The conclusion should be based on evidence or observations.
2. "Doubtful" suggests uncertainty, indicating lack of definitive safety.
3. Choice A is too absolute without considering potential risks.
4. Choice C uses extreme language without proper evidence.
5. Choice D is overly definitive without considering varying levels of contamination. Therefore, choice B is the most reasonable conclusion.
A scientist identifies a strand of RNA that can be directly used to code for important viral proteins during viral replication. What have they found?
- A. RNA major
- B. -RNA
- C. (+RNA)
- D. RNA minor
Correct Answer: C
Rationale: The correct answer is C: (+RNA). This indicates that the scientist found a positive-sense RNA strand that can be directly translated by host cell machinery to produce viral proteins. Positive-sense RNA can act as messenger RNA, allowing immediate protein synthesis during viral replication. Choice A (RNA major) and D (RNA minor) are not standard terms used to describe RNA strands in virology. Choice B (-RNA) indicates a negative-sense RNA strand, which requires transcription to form a complementary positive-sense strand before protein synthesis. Thus, the identification of a strand of RNA that directly codes for viral proteins aligns with the characteristics of a positive-sense RNA strand.
Which bacteria produce the diphtheria toxin?
- A. Corynebacterium diphtheriae
- B. Bacillus anthracis
- C. Clostridium tetani
- D. Listeria monocytogenes
Correct Answer: A
Rationale: The correct answer is A: Corynebacterium diphtheriae. This bacterium produces the diphtheria toxin, which is responsible for causing diphtheria. The other choices, B, C, and D, are incorrect because Bacillus anthracis produces anthrax toxins, Clostridium tetani produces tetanus toxin, and Listeria monocytogenes does not produce the diphtheria toxin. Understanding the specific bacteria-toxin associations is crucial in correctly identifying the pathogen responsible for a particular disease.
When examining a patient presumptively diagnosed with food toxicoinfection, a doctor on duty has detected symptoms characteristic of botulism. The patient named the meals he ate the day before. What is the most probable cause of infection?
- A. Homemade canned meat
- B. Custard pastry from a private bakery
- C. Sour cream from a local dairy factory
- D. Strawberries from a suburban vegetable garden
Correct Answer: A
Rationale: The correct answer is A: Homemade canned meat. Botulism is caused by the Clostridium botulinum bacteria, which thrives in low-oxygen environments like improperly canned food. Homemade canned meat poses a higher risk of contamination as it may not have been processed correctly, allowing the bacteria to grow and produce toxins. Custard pastry, sour cream, and strawberries are less likely to cause botulism as they are not typically associated with the bacteria unless improperly handled or stored. Homemade canned meat is the most probable cause based on the characteristic symptoms of botulism and the conditions that favor the growth of Clostridium botulinum in canned food.