A Gram-negative bacterium producing a blue-green pigment and having a fruity odor was isolated from a patient's wound infection. What is the likely causative agent?

Correct Answer: A

Rationale: Step-by-step rationale: 1. Blue-green pigment + fruity odor are characteristic of Pseudomonas aeruginosa. 2. P. aeruginosa is a Gram-negative bacterium commonly associated with wound infections. 3. P. aeruginosa is known for its ability to produce pyocyanin (blue-green pigment) and a sweet, fruity odor. 4. Other choices like E. coli, K. pneumoniae, and P. mirabilis do not typically produce blue-green pigment or fruity odor. 5. Therefore, based on the characteristics observed, the likely causative agent is Pseudomonas aeruginosa. Summary of other choices: - Escherichia coli: Does not produce blue-green pigment or fruity odor. - Klebsiella pneumoniae: Does not typically produce blue-green pigment or fruity odor. - Proteus mirabilis: Does not produce blue-green pigment or fruity odor.

Correct Answer: C

Rationale: The correct answer is C: Bacteriophages are viruses that infect bacteria. Firstly, bacteriophages are viruses, not white blood cells or bacteria. They specifically target and infect bacteria, not fungi. This is known as a bacteriophage cycle where the virus injects its genetic material into the bacterial cell to replicate and eventually lyse the cell. This process is specific to bacteria and distinguishes bacteriophages from other microorganisms. Therefore, the correct answer is C as it accurately describes the nature and function of bacteriophages.

Correct Answer: D

Rationale: Certainly! The correct answer is D because all three options (A, B, and C) can be analyzed in the diagnosis of sexually transmitted infections. Genital ulcer secretions can reveal the presence of pathogens causing STIs, lymph node punctate can indicate systemic infection, and serum can be tested for specific STI antibodies. Therefore, all these clinical specimens are essential for a comprehensive diagnosis of sexually transmitted infections. The other choices (A, B, C) are incorrect as they individually represent important specimens used in the diagnosis process.

Correct Answer: A

Rationale: The correct answer is A: Clostridium perfringens. This bacterium is an anaerobic, Gram-positive rod that forms terminal spores and produces gas. It is commonly associated with wound infections and gas gangrene. Clostridium botulinum causes botulism and does not typically present with gas production. Bacillus anthracis is an aerobic, Gram-positive spore-forming bacterium causing anthrax. Clostridium tetani causes tetanus and does not produce gas. Thus, based on the characteristics described in the question, Clostridium perfringens is the most likely causative agent.

Correct Answer: A

Rationale: The correct answer is A: Oxidation. Phase I reactions in biotransformation involve introducing or unmasking functional groups through oxidation, reduction, or hydrolysis. Oxidation reactions typically involve the addition of an oxygen atom or removal of hydrogen atoms, making them common phase I reactions. In this process, enzymes like cytochrome P450 play a crucial role in catalyzing the oxidation reactions. Conjugation (B), acetylation (C), and glucuronidation (D) are all examples of phase II reactions, which involve the conjugation of the drug or metabolite with endogenous compounds to increase water solubility for excretion. These reactions typically follow phase I reactions and are not classified as phase I reactions in biotransformation.

Correct Answer: B

Rationale: The correct answer is B: Gram-negative bacteria. Gram-negative bacteria have an outer membrane containing lipopolysaccharides (LPS). In the Gram staining technique, these bacteria appear pink/red due to the thin peptidoglycan layer, which allows the crystal violet stain to be washed out, revealing the safranin counterstain. Gram-positive bacteria (choice A) have a thick peptidoglycan layer but lack an outer membrane with LPS. Choice C is incorrect since only Gram-negative bacteria possess LPS in their outer membrane. Choice D is incorrect as all bacteria can be classified as either Gram-positive or Gram-negative based on their cell wall structure.

Correct Answer: C

Rationale: The correct answer is C because Marburg virus and Ebola virus belong to the Filoviridae family. These viruses are characterized by their filamentous shape and are known to cause severe hemorrhagic fever in humans. Both viruses have caused outbreaks with high mortality rates. Choice A (Lassa virus and lymphocytic choriomeningitis viruses) are not part of the Filoviridae family. They belong to the Arenaviridae family, which also includes viruses that cause hemorrhagic fevers. Choice B (Chikungunya virus and Sindbis virus) are arboviruses belonging to the Togaviridae family, which are not related to the Filoviridae family. Choice D (Crimean-Congo virus and Hantaan virus) are part of the Nairoviridae and Hantaviridae families, respectively, and not the Filoviridae family.

Correct Answer: B

Rationale: The correct answer is B: pertussis toxin. This toxin is the most important virulence factor of Bordetella pertussis because it plays a key role in causing the characteristic symptoms of whooping cough. Pertussis toxin interferes with the host's immune response, leading to inflammation and tissue damage in the respiratory tract. The other choices (A: the flagellum, C: P fimbriae, D: mannose-resistant adhesins) are important for bacterial attachment and colonization, but they do not directly contribute to the severity of the disease like pertussis toxin does.

Correct Answer: C

Rationale: The correct answer is C: Fungi. Molds are a type of fungi, which are eukaryotic organisms characterized by having cell walls made of chitin. Fungi are distinct from protozoans (single-celled eukaryotes), archaea (prokaryotes), and algae (photosynthetic eukaryotes). Fungi, including molds, obtain nutrients through absorption and play crucial roles in decomposition and nutrient cycling. Therefore, molds belong to the group of eukaryotic organisms known as fungi.