Microscopy of a wound smear revealed Gram-positive rods with terminal spores resembling drumsticks. What microorganism is most likely responsible?

Correct Answer: A

Rationale: The correct answer is A: Clostridium tetani. The presence of Gram-positive rods with terminal spores resembling drumsticks indicates Clostridium tetani, the causative agent of tetanus. This bacterium forms spores at one end, giving it a drumstick appearance under the microscope. Clostridium perfringens (B) and Clostridium botulinum (D) do not have terminal spores. Bacillus anthracis (C) forms spores but typically appears as a square-ended or bamboo stick shape. Therefore, based on the microscopy findings, Clostridium tetani is the most likely microorganism responsible for the wound infection.

Correct Answer: C

Rationale: The correct answer is C (60 years) because as individuals age, their immune system weakens, making them more susceptible to infectious diseases. Around the age of 60, people are more likely to succumb to infections, leading to a higher mortality rate. Choices A, B, and D are incorrect because they are younger ages, and the likelihood of infectious diseases causing a significant proportion of deaths increases with age.

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: D

Rationale: The correct answer is D: salmonellosis. Zoonotic diseases are those that can be transmitted from animals to humans. Salmonella is not directly transmitted from animals to humans, instead, it is typically transmitted through contaminated food or water. Brucellosis (A), undulant fever (B), and plague (C) are all zoonotic diseases that can be directly transmitted from animals to humans through various means. Therefore, salmonellosis does not fit the definition of a zoonotic disease, making it the correct answer.

Correct Answer: A

Rationale: The correct answer is A: Streptococcus pneumoniae. The presence of Gram-positive cocci in pairs indicates a bacterial morphology consistent with Streptococcus pneumoniae, a common cause of pneumonia. This bacterium is known to appear in pairs or short chains on Gram stain. Staphylococcus aureus (B) typically presents as clusters of Gram-positive cocci, Neisseria meningitidis (C) is a Gram-negative diplococcus, and Klebsiella pneumoniae (D) is a Gram-negative rod, making them less likely causative agents in this scenario.

Correct Answer: A

Rationale: The correct answer is A: Balantidiasis. The large ciliated protozoa with a kidney-shaped macronucleus described in the stool sample is consistent with Balantidium coli, the causative agent of balantidiasis. Balantidium coli is the only ciliated protozoan parasite that infects humans and presents with these specific characteristics. Giardiasis (B) is caused by Giardia intestinalis, which is flagellated, not ciliated. Amoebiasis (C) is caused by Entamoeba histolytica, which has an amoeboid shape, not ciliated. Trichomoniasis (D) is caused by Trichomonas vaginalis, which is a flagellated protozoan and does not have a kidney-shaped macronucleus. Hence, the correct diagnosis in this case is Balantidiasis.

Correct Answer: B

Rationale: The correct answer is B because the capsule of bacteria is mainly composed of polysaccharides or polypeptides. This outer layer helps bacteria evade the host's immune system and protects them from desiccation. Peptidoglycan (choice A) is a component of the bacterial cell wall, not the capsule. Flagellin (choice C) is a protein component of the bacterial flagella, not the capsule. Choice D is incorrect as the capsule is indeed composed of polysaccharides or polypeptides.

Correct Answer: A

Rationale: The correct answer is A: Yersinia pestis. Y. pestis causes bubonic plague, characterized by enlarged, painful lymph nodes called buboes. The Gram-negative rods with a safety pin appearance are seen on Gram stain of Y. pestis. The other choices are incorrect because Francisella tularensis causes tularemia, not lymphadenitis with safety pin appearance. Brucella abortus causes brucellosis, which typically does not present with lymphadenitis. Clostridium botulinum causes botulism, which is not associated with lymphadenitis or safety pin appearance.

Correct Answer: A

Rationale: Rationale: 1. Listeria monocytogenes is a Gram-positive bacterium known for causing foodborne illnesses. 2. Gram-negative bacteria have a different cell wall structure than Gram-positive bacteria, making choice A correct. 3. Choice B is incorrect as Listeria monocytogenes is not encapsulated or sporulating. 4. Choice C is incorrect as Listeria monocytogenes does have a cell wall. 5. Choice D is incorrect as Listeria monocytogenes is indeed a Gram-positive coccobacilli.