Microscopic examination of cerebrospinal fluid revealed Gram-negative diplococci. The patient presented with fever, headache, and neck stiffness. What is the most likely causative agent?

Correct Answer: A

Rationale: The correct answer is A: Neisseria meningitidis. This bacterium is a Gram-negative diplococcus commonly associated with meningitis. The patient's symptoms of fever, headache, and neck stiffness are classic signs of meningococcal meningitis. Neisseria meningitidis is known to cause outbreaks in crowded settings. Streptococcus pneumoniae (Choice B) is a common cause of bacterial meningitis but typically appears as Gram-positive cocci. Haemophilus influenzae (Choice C) can also cause meningitis but is more commonly seen in unvaccinated children. Klebsiella pneumoniae (Choice D) is a Gram-negative bacterium but is not a typical causative agent of meningitis.

Correct Answer: D

Rationale: The bacitracin sensitivity test is used to differentiate between different types of streptococci. Group A streptococci are sensitive to bacitracin, which means they will show inhibition around the bacitracin disk. This sensitivity is a characteristic feature of group A streptococci and helps in their identification. Staphylococci, pneumococci, and intestinal bacteria do not exhibit this sensitivity to bacitracin. Therefore, the correct answer is D: group A streptococci.

Correct Answer: A

Rationale: The correct answer is A: Clostridium perfringens. Clostridium perfringens is a Gram-positive, spore-forming bacterium that is anaerobic and produces gas. It is commonly associated with wound infections and gas gangrene. Clostridium tetani causes tetanus, not wound infections. Clostridium botulinum causes botulism, not typically associated with wound infections. Bacillus anthracis causes anthrax, which does not typically produce gas in wound infections.

Correct Answer: A

Rationale: The correct answer is A: Bacteriological. This method involves isolating and culturing the causative bacteria from the wound material to determine the species. This allows for further testing to confirm gaseous gangrene and identify the specific pathogen. Choice B: Allergic is incorrect as it pertains to immune responses, not identifying bacteria. Choice C: Bacterioscopic is incorrect as it refers to microscopic examination of bacteria, not species identification. Choice D: Serological is incorrect as it involves testing for antibodies in the blood, not identifying the causative agent directly.

Correct Answer: C

Rationale: The correct answer is C: ensure survival under harsh conditions. Bacterial endospores are dormant, resistant structures that form under adverse conditions to protect the bacterial DNA and allow the bacterium to survive extreme environments. This function is crucial for the bacterium's long-term survival. Choice A is incorrect as endospores do not directly produce exotoxins. Choice B is incorrect as endospores do not store nutrients but rather protect the bacterium's genetic material. Choice D is incorrect as endospores do not enhance motility but rather enable survival during unfavorable conditions.

Correct Answer: B

Rationale: The correct answer is B: Fluconazole. Rationale: 1. Candidiasis is a fungal infection, so an antimycotic agent is needed. 2. β-lactam antibiotics like ampicillin can lead to fungal overgrowth, necessitating an antimycotic. 3. Fluconazole is an antifungal agent effective against Candida species. 4. Streptomycin is an antibiotic, not an antifungal. 5. Phthalylsulfathiazole is an antibacterial sulfonamide, not an antifungal. 6. Ampicillin is an antibiotic, not an antifungal.

Correct Answer: A

Rationale: The correct answer is A: Clostridium tetani. Clostridium tetani is responsible for causing tetanus due to its production of tetanospasmin toxin. This neurotoxin leads to muscle stiffness and spasms characteristic of tetanus. Clostridium perfringens is associated with gas gangrene, not tetanus. Streptococcus pyogenes causes strep throat and skin infections, not tetanus. Escherichia coli is a common gut bacteria and is not responsible for tetanus. Therefore, choice A is the correct answer for causing tetanus.

Correct Answer: A

Rationale: The correct answer is A: Clostridium botulinum. This bacterium produces the neurotoxin responsible for botulism. It thrives in anaerobic environments like improperly canned foods. Clostridium difficile (B) causes colitis, not botulism. Staphylococcus aureus (C) causes food poisoning but not botulism. Escherichia coli (D) can cause gastrointestinal illness but not botulism.

Correct Answer: C

Rationale: The correct answer is C because bacterial enzymes like amylase and protease catalyze biochemical reactions like digestion. Amylase breaks down carbohydrates, while protease breaks down proteins. This process is essential for bacterial metabolism and nutrient acquisition. Choice A (Break down toxins) is incorrect because bacterial enzymes are primarily involved in nutrient breakdown, not toxin degradation. Choice B (Facilitate movement) is incorrect as enzymes are not directly involved in bacterial movement. Choice D (Promote spore formation) is incorrect because enzymes like amylase and protease are not directly involved in spore formation.