microbiology chapter 11 test bank

Correct Answer: A

Rationale: The most likely causative agent is Corynebacterium diphtheriae. Step 1: Presence of rod-shaped bacteria indicates a bacillus. Step 2: Polar granules suggest metachromatic granules seen in C. diphtheriae. Step 3: C. diphtheriae causes diphtheria, which presents with sore throat. Summary: B is incorrect as S. pneumoniae is a cocci, not a bacillus. C is incorrect as H. influenzae is a pleomorphic coccobacillus. D is incorrect as K. pneumoniae is a large, encapsulated bacillus.

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.

Correct Answer: A

Rationale: The most likely causative agent is Corynebacterium diphtheriae. Step 1: Presence of rod-shaped bacteria indicates a bacillus. Step 2: Polar granules suggest metachromatic granules seen in C. diphtheriae. Step 3: C. diphtheriae causes diphtheria, which presents with sore throat. Summary: B is incorrect as S. pneumoniae is a cocci, not a bacillus. C is incorrect as H. influenzae is a pleomorphic coccobacillus. D is incorrect as K. pneumoniae is a large, encapsulated bacillus.

Correct Answer: C

Rationale: The correct answer is C because Leptospira cannot be cultivated on blood and chocolate agar. The bacterium requires specialized media such as Ellinghausen-McCullough-Johnson-Harris (EMJH) medium for growth. Blood and chocolate agar do not provide the necessary nutrients for the bacterium's growth. Leptospira is a fastidious organism that has unique culture requirements. Therefore, the statement that Leptospira can be cultivated on blood and chocolate agar is incorrect. The other choices are correct: A - Leptospirosis is an acute infectious disease with a typical geographic distribution, B - Reservoirs of leptospira are different wild and domestic animals, mainly rodents, and D - Doxycycline and penicillins are drugs of choice for the treatment of leptospirosis.

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.