Microscopy of dental plaque revealed unicellular organisms. Their cytoplasm had two distinct layers, barely visible core, wide pseudopodia. The patient is most likely to have:

Correct Answer: D

Rationale: The correct answer is D: Trichomonas tenax. Trichomonas tenax is a flagellated protozoan that is commonly found in the oral cavity, specifically in dental plaque. The description provided in the question matches the characteristics of Trichomonas tenax, such as unicellular structure, distinct layers in the cytoplasm, wide pseudopodia, and barely visible core. Entamoeba gingivalis (choice A) and Entamoeba histolytica (choice B) are amoebas, not flagellated protozoa, and they do not exhibit the characteristics described in the question. Lamblia (choice C) is also an incorrect choice as it is a different type of protozoan that does not match the description provided.

Correct Answer: A

Rationale: The correct answer is A: Gram-negative stain. Pseudomonas aeruginosa is a gram-negative bacterium, as indicated by the bluish-green pus color. This bacterium has an outer membrane that retains the crystal violet stain, making it appear pink/red after the counterstain with safranin in Gram staining. The other choices are incorrect because Pseudomonas aeruginosa does not typically form spores (B), has a rod-shaped morphology rather than a coccal form (C), and does not exhibit cell pairing (D).

Correct Answer: A

Rationale: The correct answer is A: Actinomycosis. This is a chronic bacterial infection caused by Actinomyces species. In this case, the description of dense yellow-green colored focus, white granules in purulent masses, and presence of fungal druses, plasma cells, xanthome cells, and macrophages all match the characteristics of actinomycosis. Actinomycosis typically presents with abscess formation containing sulfur granules, which are yellowish and granular. The other choices (B: Furuncle, C: Carbuncle, D: Syphilis) do not fit the clinical and histological features described in the question, making them incorrect options.

Correct Answer: A

Rationale: The correct answer is A: Clostridium perfringens. Gas gangrene is caused by Clostridium perfringens, a Gram-positive rod bacterium that produces spores. This bacterium is anaerobic and commonly found in soil, where it forms spores that can survive harsh conditions. Clostridium tetani causes tetanus, not gas gangrene. Bacillus anthracis causes anthrax, not gas gangrene. Clostridium botulinum causes botulism, not gas gangrene. Therefore, based on the characteristics of the microorganism described in the question, Clostridium perfringens is the correct identification.

Correct Answer: A

Rationale: The correct answer is A: ethylene oxide. Ethylene oxide is a toxic, odorless gas commonly used as a sterilizing agent in healthcare settings due to its ability to effectively kill bacteria, viruses, and fungi. It is a highly reactive compound that can penetrate porous materials, making it an ideal choice for sterilization purposes. Incorrect choices: B: Carbon dioxide is not used as a sterilizing agent and is not toxic. C: Carbon monoxide is not commonly used for sterilization and has a distinct odor. D: Propane is not used for sterilization in healthcare settings and is not odorless.

Correct Answer: A

Rationale: The correct answer is A: Nystatin. Nystatin is specifically used to treat intestinal candidiasis because it targets and eliminates the Candida species responsible for the infection. It is not absorbed systemically, acting only locally in the gastrointestinal tract. Griseofulvin (B) is mainly used to treat fungal skin infections, not intestinal candidiasis. Undecyne (C) is an antifungal agent used for skin infections, not for intestinal candidiasis. Amphotericin B (D) is a potent antifungal agent used for systemic fungal infections, not specifically for intestinal candidiasis.

Correct Answer: D

Rationale: The correct answer is D: Relenza and Tamiflu. Both Relenza and Tamiflu are anti-influenza drugs that target the neuraminidase enzyme of the influenza virus, thereby inhibiting its replication and spread. Maxi Grip (A) is not an anti-influenza drug, Theraflu (B) contains different active ingredients, and Amantadine and Rimantadine (C) target a different viral protein, M2 ion channel. Therefore, choices A, B, and C are incorrect as they do not specifically target neuraminidase for influenza treatment.

Correct Answer: A

Rationale: Rationale: Shigella dysenteriae produces Shiga toxin, which inhibits protein synthesis by inactivating the 60S ribosomal subunit. This disrupts the translation process, leading to cell death. Escherichia coli (choice B) does not produce a toxin that inhibits protein synthesis. Clostridium tetani (choice C) produces tetanospasmin, which affects the nervous system. Staphylococcus aureus (choice D) produces toxins that cause food poisoning but do not inhibit protein synthesis.

Correct Answer: A

Rationale: The correct answer is A: C. botulinum. The description of gram-positive bacilli with subterminal staining defect and tennis racket appearance is characteristic of Clostridium botulinum. The subterminal staining defect indicates the presence of spores, a feature of Clostridium species. The tennis racket appearance refers to the characteristic shape of C. botulinum spores. Choice B, P. vulgaris, is a gram-negative bacterium and doesn't match the description. Choice C, E. coli, is a gram-negative bacillus and doesn't exhibit the subterminal staining defect described. Choice D, S. aureus, is a gram-positive cocci and does not resemble the tennis racket appearance described.