Which of the following is a characteristic of Gram-positive bacteria?

Correct Answer: C

Rationale: The correct answer is C: Thick peptidoglycan layer. Gram-positive bacteria have a thick peptidoglycan layer in their cell wall, which retains the crystal violet stain in the Gram staining process, leading to a purple color. This thick layer is a defining characteristic of Gram-positive bacteria. Rationale: A: Thin peptidoglycan layer is incorrect because Gram-positive bacteria have a thick peptidoglycan layer. B: Presence of an outer membrane is incorrect because Gram-positive bacteria lack an outer membrane. D: Presence of lipopolysaccharides is incorrect because lipopolysaccharides are typically found in the outer membrane of Gram-negative bacteria, not Gram-positive bacteria.

Correct Answer: B

Rationale: The correct answer is B: Legionella and Neisseria are both gram-negative aerobic rods and cocci. Legionella is a rod-shaped bacterium, while Neisseria is a diplococcus. Both are aerobic, meaning they require oxygen for growth. The other choices are incorrect because Legionella and Neisseria are not facultative anaerobes (A), spirochetes (C), or anaerobic cocci (D). Understanding the characteristics of these bacteria helps in differentiating and selecting the correct answer.

Correct Answer: A

Rationale: The correct answer is A: Shigella dysenteriae. It is the likely causative agent because it is a non-lactose-fermenting, Gram-negative rod commonly associated with severe diarrhea. Shigella dysenteriae specifically causes bacillary dysentery. Other choices are incorrect because: B: Escherichia coli is a lactose-fermenting bacterium commonly found in the gut and not typically associated with severe diarrhea. C: Salmonella typhi causes typhoid fever, not severe diarrhea. D: Proteus mirabilis is a urease-positive bacterium associated with urinary tract infections, not severe diarrhea.

Correct Answer: D

Rationale: The correct answer is D: active transport system. Permeases are specific carriers that actively transport molecules across a cell membrane against their concentration gradient, requiring energy input. This process is known as active transport, which is essential for maintaining cellular homeostasis and allowing the cell to accumulate specific molecules. Facilitated diffusion (A) and passive transport (B) both involve the movement of molecules down their concentration gradient without the need for energy input. Simple diffusion (C) also does not involve specific carriers and relies on the natural movement of molecules from areas of high concentration to low concentration. Therefore, the correct choice is D as permeases specifically function in active transport systems.

Correct Answer: C

Rationale: The correct answer is C: Biological test, bacteriological. Botulism is caused by the toxin produced by Clostridium botulinum bacteria. To diagnose botulism, biological tests such as detecting the toxin in patient samples and bacteriological tests to identify the bacteria are crucial. These tests confirm the presence of the bacteria and its toxin, providing a definitive diagnosis. Choice A is incorrect as it does not specify any relevant diagnostic methods. Choice B is incorrect because mycological tests are not relevant for diagnosing botulism caused by a bacterial toxin. Choice D is incorrect as allergic tests and serological tests are not used for diagnosing botulism.

Correct Answer: C

Rationale: Step-by-step rationale for why choice C (Adenoviridae) is correct: 1. Adenoviruses commonly cause respiratory illnesses such as the common cold and bronchitis. 2. They are highly contagious and easily spread through respiratory secretions. 3. Adenoviruses are a common cause of viral conjunctivitis as well. 4. Other choices are incorrect because herpesviruses (choice A) typically cause different types of infections, papovaviruses (choice B) are not common respiratory pathogens, and poxviruses (choice D) are not typically associated with respiratory illnesses.

Correct Answer: A

Rationale: The correct answer is A: Brill's disease. Brill's disease is a relapse of typhus that occurs in patients who had typhus in their youth. The patient's history of having typhus at 15 years old is a key indicator. Brill's disease is characterized by symptoms such as rash, fever, and dizziness, which align with the patient's current presentation. Summary of other choices: B: Typhoid fever - While typhoid fever may present with similar symptoms to typhus, the patient's history of having typhus in the past makes this less likely. C: Measles - Measles does not typically present with dizziness, and the patient's history of typhus in the past is more indicative of Brill's disease. D: Rubella - Rubella does not typically cause dizziness, and the patient's history of typhus in the past points more towards Brill's disease.

Correct Answer: B

Rationale: The correct answer is B because peritrichous bacteria have flagella distributed all over their surface, allowing them to move in various directions. Choice A is incorrect because bacteria with a single flagellum at one pole are called monotrichous. Choice C is incorrect as bacteria with a single flagellum at each pole are known as amphitrichous. Choice D is incorrect because peritrichous bacteria have multiple flagella all over their surface, not limited to one or both poles.

Correct Answer: A

Rationale: The correct answer is A: Streptococcus pneumoniae. This bacterium is the most likely causative agent because it is a Gram-positive cocci in pairs with a capsule, which matches the description provided. S. pneumoniae is a common cause of bacterial pharyngitis and can present with sore throat. Summary of other choices: B: Staphylococcus aureus is a Gram-positive cocci in clusters, not pairs, and is not typically associated with sore throat. C: Neisseria meningitidis is a Gram-negative diplococcus and more commonly causes meningitis or septicemia, not sore throat. D: Klebsiella pneumoniae is a Gram-negative rod bacterium, not a Gram-positive cocci, and is not a common cause of sore throat.