A patient with severe pneumonia had a sputum culture revealing Gram-negative rods that are non-lactose fermenters. What is the most likely causative agent?

Correct Answer: A

Rationale: The correct answer is A: Pseudomonas aeruginosa. This is because Pseudomonas aeruginosa is a common Gram-negative rod that is a non-lactose fermenter and a common cause of severe pneumonia, especially in immunocompromised individuals. It is also known for its resistance to many antibiotics, making it difficult to treat. Summary of other choices: B: Escherichia coli is a lactose fermenter and is not commonly associated with severe pneumonia. C: Klebsiella pneumoniae is a lactose fermenter and is more commonly associated with pneumonia in alcoholics or debilitated patients. D: Enterobacter cloacae is a lactose fermenter and is not a common cause of severe pneumonia.

Correct Answer: C

Rationale: The correct answer is C, as Gram-negative bacteria have a cell wall containing lipopolysaccharides. This outer membrane structure is unique to Gram-negative bacteria and plays a critical role in pathogenicity and immune response. Teichoic acid (choice A) is found in Gram-positive bacteria. The cell wall of Gram-negative bacteria is thinner than that of Gram-positive bacteria (choice B). The cell wall of Gram-negative bacteria is not composed entirely of peptidoglycan (choice D), as it also contains other components like lipopolysaccharides.

Correct Answer: C

Rationale: Step-by-step rationale: 1. Aspergillus flavus is a fungus known to produce aflatoxin. 2. Aflatoxin is a potent carcinogen found in contaminated food. 3. Candida albicans is a yeast species not associated with aflatoxin production. 4. Claviceps purpurea is a fungus that produces ergot alkaloids, not aflatoxin. 5. Staphylococcus aureus is a bacterium known for causing food poisoning, not aflatoxin production. Summary: Aspergillus flavus is the correct answer as it is the organism known to produce aflatoxin, a carcinogenic substance. Other choices are incorrect as they are not associated with aflatoxin production.

Correct Answer: C

Rationale: The correct answer is C: IFA - Immunofluorescence assay. Toxoplasmosis and chronic gonorrhea can be detected using serological tests like IFA. IFA detects specific antibodies in the patient's serum by using fluorescently labeled antibodies. This method is highly sensitive and specific for detecting both acute and latent infections. Explanation of Incorrect Choices: A: RIHA - Reverse indirect hemagglutination assay - This test is not commonly used for detecting toxoplasmosis or chronic gonorrhea. B: RDHA - Reverse direct hemagglutination assay - This test is not typically used for these specific infections. D: Immunoblot analysis - While Immunoblot analysis is a useful confirmatory test for certain infections, it is not the primary method for detecting toxoplasmosis or chronic gonorrhea.

Correct Answer: C

Rationale: The correct answer is C: Mumps. Group II diseases are vaccine-preventable diseases that are communicable and can cause outbreaks. Mumps fits this criteria as it is preventable through vaccination, easily transmitted through respiratory droplets, and can lead to outbreaks in communities. Anthrax (A) is a zoonotic disease, Lyme disease (B) is transmitted by ticks, and Smallpox (D) has been eradicated.

Correct Answer: D

Rationale: The correct answer is D. Clostridium botulinum produces botulinum toxin, Salmonella enterica produces salmonella toxin, and certain strains of Escherichia coli produce toxins like shiga toxin. These toxins can cause severe foodborne illnesses. Therefore, all of the above bacteria can produce toxins that lead to foodborne illnesses. Choices A, B, and C alone are incorrect because each of these bacteria individually can produce toxins that lead to foodborne illnesses.

Correct Answer: A

Rationale: The correct answer is A: Carbenicillin disodium. Carbenicillin is a semisynthetic penicillin that has marked activity against Pseudomonas aeruginosa. This is due to its extended spectrum of activity and increased stability against beta-lactamases produced by Pseudomonas aeruginosa. Carbenicillin is commonly used to treat infections caused by this bacterium. Choice B: Benzylpenicillin (Penicillin G) has limited activity against Pseudomonas aeruginosa. Choice C: Methicillin is not effective against Pseudomonas aeruginosa. Choice D: Oxacillin also has limited activity against Pseudomonas aeruginosa. In summary, Carbenicillin is the correct choice due to its marked activity against Pseudomonas aeruginosa compared to the other penicillins listed.

Correct Answer: C

Rationale: The correct answer is C: Plague. Yersinia pestis is the bacterium responsible for causing the bubonic, septicemic, and pneumonic plague. The bacterium is transmitted to humans through infected flea bites or handling infected animals. Tonsillitis (A) is commonly caused by streptococcal bacteria, leprosy (B) is caused by Mycobacterium leprae, and rat fever (D) is another term for leptospirosis, caused by Leptospira bacteria.

Correct Answer: A

Rationale: The correct answer is A: Treponema. The characteristics described match Treponema pallidum, the causative agent of syphilis. Treponema has long, spiral shape with 8-12 regular coils. Leptospira (B) is a spirochete but has fewer coils and causes leptospirosis. Borrelia (C) is another spirochete but typically has irregular coils and causes Lyme disease. Vibrios (D) are curved rods and not spirochetes.