Which of the following bacteria IS NOT associated with skin infections?

Correct Answer: D

Rationale: Correct Answer: D (Clostridium difficile) Rationale: 1. Clostridium difficile is primarily associated with gastrointestinal infections, particularly antibiotic-associated colitis. 2. Staphylococcus aureus, Clostridium perfringens, and Pseudomonas aeruginosa are commonly associated with skin infections. 3. Staphylococcus aureus can cause impetigo, boils, and cellulitis. 4. Clostridium perfringens can cause gas gangrene. 5. Pseudomonas aeruginosa can cause hot tub folliculitis and swimmer's ear.

Correct Answer: A

Rationale: Step-by-step rationale: 1. Tularemia is caused by Francisella tularensis, a highly infectious bacterium. 2. Francisella tularensis is the only pathogen specifically known to cause tularemia. 3. The other choices (Bordetella pertussis, Brucella suis, Legionella sp.) are not associated with tularemia. 4. Therefore, the correct answer is A - Francisella tularensis.

Correct Answer: B

Rationale: The correct answer is B: Pseudomonas aeruginosa. This bacterium is commonly associated with hospital-acquired infections due to its ability to survive in hospital environments, resist antibiotics, and infect immunocompromised patients. Streptococcus pneumoniae (choice A) is more commonly associated with community-acquired pneumonia. Vibrio cholerae (choice C) causes cholera, a waterborne disease, and is not typically associated with hospital-acquired infections. Choice D is incorrect because Pseudomonas aeruginosa is indeed associated with hospital-acquired infections.

Correct Answer: D

Rationale: The correct answer is D: All of the above. Streptococcus pneumoniae, Mycobacterium tuberculosis, and Escherichia coli can all cause pneumonia, but through different mechanisms. S. pneumoniae is a common cause of community-acquired pneumonia, M. tuberculosis can lead to tuberculosis-related pneumonia, and E. coli can cause pneumonia in immunocompromised individuals. Therefore, all three bacteria can be responsible for causing pneumonia, making option D the correct choice. Option A, Streptococcus pneumoniae, is correct but does not cover all possible causes of pneumonia. Option B, Mycobacterium tuberculosis, is too specific and does not include other common causes. Option C, Escherichia coli, is also a possible cause of pneumonia but does not account for all potential pathogens.

Correct Answer: B

Rationale: The correct answer is B: Plasmids. Plasmids are extrachromosomal DNA molecules found in bacteria that can replicate independently of the bacterial chromosome. They carry additional genetic information, such as antibiotic resistance genes or virulence factors. Mesosomes (choice A) are not involved in carrying genetic information; they are infoldings of the cell membrane. Ribosomes (choice C) are cellular organelles responsible for protein synthesis, not carriers of genetic information. Choice D is incorrect as plasmids are indeed extrachromosomal carriers of genetic information in bacteria.

Correct Answer: B

Rationale: The correct answer is B: Bacillus subtilis. Bacillus subtilis is a thermophilic bacterium capable of surviving in extreme heat due to its heat-resistant spores. It forms spores when exposed to unfavorable conditions, allowing it to withstand high temperatures. Escherichia coli (A), Staphylococcus aureus (C), and Clostridium botulinum (D) are mesophilic bacteria that do not have the same heat resistance mechanisms as Bacillus subtilis, making them unable to survive in extreme heat conditions.

Correct Answer: A

Rationale: Rationale: 1. Gram-positive cocci in pairs indicate Streptococcus pneumoniae. 2. Presence of a capsule points to S. pneumoniae as it has a polysaccharide capsule. 3. S. pneumoniae commonly causes sore throat. 4. Neisseria meningitidis, Haemophilus influenzae, and Klebsiella pneumoniae are not typically associated with sore throat.

Correct Answer: A

Rationale: The correct answer is A: Staphylococcus aureus. Staphylococcus aureus is a Gram-positive cocci that is catalase-positive and coagulase-positive, making it the most likely causative agent for the wound infection. Catalase-positive bacteria produce the enzyme catalase, which helps break down hydrogen peroxide. Coagulase-positive bacteria produce the enzyme coagulase, which causes the plasma proteins to clot. Staphylococcus epidermidis is catalase-positive but coagulase-negative, making it less likely to cause a wound infection. Streptococcus pyogenes is catalase-negative, and Enterococcus faecalis is catalase-negative and coagulase-negative, so they are less likely to be the causative agent.

Correct Answer: B

Rationale: The Ziehl-Neelsen stain is specifically designed to detect acid-fast bacteria like Mycobacterium tuberculosis. It utilizes a carbol fuchsin dye that binds to the high lipid content in the cell wall of acid-fast bacteria, making them appear red under a microscope. This staining method is crucial for the diagnosis of tuberculosis and leprosy. Gram-positive bacteria (Choice A) are not detected by this stain since they have a different cell wall structure. Capsulated bacteria (Choice C) and fungal spores (Choice D) also have distinct characteristics that are not targeted by the Ziehl-Neelsen stain.