Correct Answer: A

Rationale: The correct answer is A: Streptococcus pneumoniae. This bacteria is known for causing pneumonia due to its ability to infect the lungs and cause inflammation leading to pneumonia symptoms. It is a common cause of community-acquired pneumonia. Mycobacterium tuberculosis (B) causes tuberculosis, not pneumonia. Escherichia coli (C) is associated with urinary tract infections and gastrointestinal infections, not pneumonia. Pseudomonas aeruginosa (D) is known to cause infections in immunocompromised individuals but is not a common cause of pneumonia.

Correct Answer: D

Rationale: The correct answer is D: Proteus vulgaris. This is because Proteus species are non-lactose-fermenting Gram-negative rods that are known to produce gas in nutrient broths. Proteus vulgaris is commonly associated with urinary tract infections and can also cause abdominal infections. A: Salmonella typhi typically causes typhoid fever and is not known to produce gas in nutrient broths. B: Shigella dysenteriae is a causative agent of dysentery and does not typically produce gas in nutrient broths. C: Escherichia coli is a lactose-fermenting bacterium and does not fit the description of the organism in the stool culture.

Correct Answer: D

Rationale: The correct answer is D: All of the above. Hepatitis B infection can present with jaundice due to liver inflammation, elevated serum aminotransferase levels due to liver damage, and sometimes no symptoms in the acute phase. This comprehensive presentation covers the spectrum of possible clinical manifestations of hepatitis B infection. Choices A and B are correct as they are common manifestations of hepatitis B infection. Choice C is incorrect as hepatitis B infection can indeed present with symptoms, making option D the most appropriate choice.

Correct Answer: D

Rationale: The correct answer is D, "All of the above," because all three bacteria listed (Vibrio cholerae, Clostridium difficile, Escherichia coli) produce toxins that can cause severe gastrointestinal illness. Vibrio cholerae produces cholera toxin leading to severe diarrhea. Clostridium difficile produces toxins causing antibiotic-associated diarrhea. Escherichia coli can produce toxins such as Shiga toxin causing severe gastrointestinal symptoms. Therefore, all the options listed are correct in producing toxins that can result in severe gastrointestinal illness.

Correct Answer: A

Rationale: The correct answer is A: Syphilitic granulomas (gummas). In the tertiary stage of syphilis, gummas, which are soft, tumor-like growths, can develop in various organs such as the skin, bones, liver, and brain. This stage typically occurs years after the initial infection and can lead to serious complications if left untreated. Purulent exudation from the urethra (B) is not specific to syphilis and may indicate other infections. Non-tender chancre (C) is characteristic of the primary stage of syphilis, not the tertiary stage. Diffuse maculopapular rash (D) is more commonly seen in the secondary stage of syphilis.