A patient being treated in the burns department has suppurative complication. The pus is of bluish- green color that is indicative of infection caused by Pseudomonas aeruginosa. What factor is typical for this causative agent?

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: Mycobacterium tuberculosis. This bacteria is responsible for causing tuberculosis because it is the specific pathogen known to infect the lungs and other parts of the body, leading to the disease. Mycobacterium tuberculosis has unique cell wall components that allow it to evade the immune system and survive in the host. Neisseria meningitidis (B) causes meningitis, not tuberculosis. Salmonella enterica (C) causes food poisoning, not tuberculosis. Streptococcus pneumoniae (D) causes pneumonia, not tuberculosis. Therefore, the correct answer is A based on the specific characteristics and pathogenicity of Mycobacterium tuberculosis.

Correct Answer: C

Rationale: The correct answer is C: Microaerophiles. These bacteria grow best in environments with low oxygen levels. They require oxygen for respiration but at lower concentrations than what is present in the atmosphere. This allows them to thrive in conditions where oxygen is limited but not completely absent. A: Facultative anaerobes can grow in both the presence and absence of oxygen. B: Obligate aerobes require oxygen for growth. D: Obligate anaerobes cannot survive in the presence of oxygen and typically grow in anaerobic environments. In summary, microaerophiles are the correct choice as they specifically thrive in low oxygen environments, distinguishing them from the other options.

Correct Answer: A

Rationale: The correct answer is A: Lassa virus. The rationale is as follows: 1. Lassa virus is a member of the Arenaviridae family, known for causing Lassa fever. 2. Arenaviridae family includes viruses with a segmented genome and are transmitted through rodents. 3. Crimean-Congo hemorrhagic fever virus (Choice B) belongs to the Bunyaviridae family, not Arenaviridae. 4. Rabies virus (Choice C) belongs to the Rhabdoviridae family, not Arenaviridae. 5. Epstein-Barr virus (Choice D) belongs to the Herpesviridae family, not Arenaviridae. In summary, Lassa virus is the correct choice as it aligns with the characteristics of the Arenaviridae family, while the other choices belong to different virus families.

Correct Answer: A

Rationale: The correct answer is A: Gram staining method. This method involves staining with gentian violet, followed by Lugol's solution, 96% alcohol decolorization, and counterstaining with safranin or water-magenta. This staining sequence allows for the differentiation of bacteria based on their cell wall composition. In the case of lobar pneumonia, the causative agent is typically a bacterium with a cell wall that retains the crystal violet stain after decolorization with alcohol, indicating a Gram-positive bacterium. Summary of Incorrect Choices: B: Ziehl-Nielsen staining is used for acid-fast bacteria like Mycobacterium tuberculosis, not for lobar pneumonia. C: Romanovsky staining is primarily used in the identification of blood cells and blood parasites, not for bacteria. D: Neisser staining is not a commonly used staining method in microbiology for bacterial identification.

Correct Answer: A

Rationale: The correct answer is A: Metronidazole. Anaerobic bacteria are sensitive to metronidazole due to its mechanism of action targeting their DNA. Metronidazole is often the drug of choice for treating infections caused by anaerobic bacteria. Gentamicin, Oxacillin, and Co-trimoxazole are not effective against anaerobes. Gentamicin is an aminoglycoside mostly used for aerobic bacteria, Oxacillin is a beta-lactam antibiotic effective against gram-positive bacteria, and Co-trimoxazole is a combination of sulfamethoxazole and trimethoprim mainly used for urinary tract infections and some respiratory infections.

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: B

Rationale: The correct answer is B: colonization. E. Coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa in the pharynx indicate colonization rather than being part of the normal resident flora. Colonization refers to the presence of these bacteria on body surfaces without causing harm. They are not considered normal flora in the pharynx but rather transient or opportunistic pathogens. Choice A is incorrect because these bacteria are not part of the normal resident flora of the pharynx. Choice C is incorrect as it implies that these bacteria are both normal flora and colonization, which is not accurate. Choice D is incorrect as there is evidence of bacterial presence, indicating colonization.

Correct Answer: D

Rationale: The correct answer is D: TCBS. Thiosulfate-citrate-bile salts-sucrose (TCBS) agar is the most selective for Vibrio cholerae due to its high salt content, bile salts, and sucrose. Vibrio cholerae can grow well in alkaline conditions, which are provided by TCBS agar. MacConkey's agar (A) is selective for gram-negative bacteria, but not specifically for Vibrio cholerae. Chocolate agar (B) is a non-selective medium suitable for fastidious organisms. SS agar (C) is selective for Salmonella and Shigella species, not Vibrio cholerae.