Gram-negative diplococci were isolated from a urethral discharge in a male patient with painful urination. What is the causative agent?

Correct Answer: A

Rationale: The correct answer is A: Neisseria gonorrhoeae. This bacterium is a gram-negative diplococci commonly associated with gonorrhea, which presents with symptoms like painful urination. Neisseria gonorrhoeae is known to infect the urethra in males. Escherichia coli, Proteus vulgaris, and Klebsiella pneumoniae are all gram-negative bacteria, but they are not typically associated with urethral discharge or gonorrhea. E. coli is commonly associated with urinary tract infections, Proteus vulgaris with wound infections, and Klebsiella pneumoniae with pneumonia and other respiratory infections. Therefore, based on the patient's symptoms and the characteristics of the bacteria, Neisseria gonorrhoeae is the most appropriate causative agent in this case.

Correct Answer: B

Rationale: The correct answer is B: Vibrio cholerae. Cholera is caused by this specific bacterium. Vibrio cholerae produces a toxin that leads to severe diarrhea and dehydration. Salmonella typhi causes typhoid fever, Escherichia coli can cause various infections but not cholera, and Shigella dysenteriae causes dysentery, not cholera. Therefore, the correct choice is B.

Correct Answer: B

Rationale: The correct answer is B: Pseudomonas aeruginosa. P. aeruginosa is known for producing pyocyanin, a green pigment. This bacterium is commonly associated with infections in immunocompromised individuals. Staphylococcus aureus (choice A) produces golden-yellow pigments, not green. Escherichia coli (choice C) and Clostridium difficile (choice D) do not produce pyocyanin. Therefore, the correct choice is B based on the characteristic pigment produced by Pseudomonas aeruginosa.

Correct Answer: A

Rationale: The correct answer is A: Escherichia coli. E. coli is commonly associated with UTIs due to its ability to colonize the urinary tract. It possesses adhesins that allow it to attach to the bladder wall, causing infection. E. coli is also a common inhabitant of the intestinal tract, making it easily able to migrate to the urinary system. Explanation of incorrect choices: B: Clostridium botulinum - This bacterium causes botulism, a rare foodborne illness, not UTIs. C: Staphylococcus aureus - Often associated with skin infections and abscesses, not UTIs. D: Bacillus cereus - Known for causing food poisoning, not UTIs.

Correct Answer: B

Rationale: The correct answer is B: Linnaeus. Linnaeus developed the binomial system of nomenclature in the 18th century. He introduced the use of a two-part naming system consisting of a genus name and a species name, known as binomial nomenclature. This system helps in organizing and categorizing living organisms systematically. Pasteur (choice A) is known for his contributions to microbiology, not nomenclature. Martini (choice C) and Jenner (choice D) are not associated with the development of the binomial system of nomenclature.