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A fecal smear from a patient with severe diarrhea revealed motile Gram-negative rods with a comma shape. What is the likely causative agent?
- A. Vibrio cholerae
- B. Shigella dysenteriae
- C. Salmonella typhi
- D. Escherichia coli
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.
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Which of the following cell organelles contain digestive enzymes?
- A. lysosomes
- B. chloroplasts
- C. peroxisomes
- D. peroxisomes
Correct Answer: C
Rationale: The correct answer is C: peroxisomes. Peroxisomes contain enzymes involved in breaking down fatty acids and detoxifying harmful substances. They do not contain digestive enzymes. Lysosomes contain digestive enzymes involved in breaking down waste materials. Chloroplasts are involved in photosynthesis and do not contain digestive enzymes. Mitochondria are involved in energy production and do not contain digestive enzymes. Therefore, the correct answer is peroxisomes.
A patient's blood culture revealed Gram-positive rods capable of spore formation. They were also motile and produced gas in nutrient broth. What is the causative agent?
- A. Clostridium perfringens
- B. Bacillus anthracis
- C. Clostridium tetani
- D. Bacillus cereus
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.
During bacteriological examination of sputum of a child with choking cough and fever there were revealed glossy smooth colonies growing on casein-charcoal agar and reminding of mercury drops. Microscopic examination revealed short Gram-negative bacteria. What microorganism was secured from the sputum?
- A. Bordetella pertussis
- B. Haemophylus influenzae
- C. Corynebacterium dyphtheriae
- D. Klebsiella pneumoniae
Correct Answer: A
Rationale: The correct answer is A: Bordetella pertussis. Glossy smooth colonies growing on casein-charcoal agar resembling mercury drops indicate Bordetella pertussis, the causative agent of whooping cough. The presence of short Gram-negative bacteria further supports this identification. Option B, Haemophilus influenzae, typically grows as small, round, translucent colonies on chocolate agar. Option C, Corynebacterium diphtheriae, forms gray colonies on tellurite agar. Option D, Klebsiella pneumoniae, appears as mucoid colonies on MacConkey agar.
Which bacteria is known for causing the disease tetanus?
- A. Clostridium tetani
- B. Clostridium perfringens
- C. Neisseria gonorrhoeae
- D. Bacillus anthracis
Correct Answer: A
Rationale: Step-by-step rationale for why A is correct:
1. Clostridium tetani is known to produce tetanus toxin.
2. The tetanus toxin causes muscle rigidity and spasms characteristic of tetanus.
3. Clostridium perfringens is associated with gas gangrene, not tetanus.
4. Neisseria gonorrhoeae causes gonorrhea, not tetanus.
5. Bacillus anthracis causes anthrax, not tetanus.
In summary, Clostridium tetani is the correct answer as it is specifically associated with causing tetanus, while the other choices are associated with different diseases.
Transduction is:
- A. Transformation
- B. Transfer of genetic material between donor and recipient bacterial cells with the help of latent phage
- C. Transfer of large plasmids from a donor cell to a recipient cell
- D. None of the above
Correct Answer: B
Rationale: Transduction is the transfer of genetic material between bacterial cells with the help of a phage (virus). This process involves a phage infecting a bacterial cell, replicating inside it, and then transferring bacterial DNA along with phage DNA to another bacterial cell. This is different from transformation (choice A) which involves the uptake of naked DNA by a bacterial cell and plasmid transfer (choice C) which involves the transfer of small, circular DNA molecules. Therefore, the correct answer is B because it specifically describes the process of transduction in bacteria, while choices A and C describe different mechanisms of genetic transfer.