Which of the following bacteria is responsible for causing the disease known as tetanus?

Correct Answer: A

Rationale: The correct answer is A: Clostridium tetani. Clostridium tetani is responsible for causing tetanus by producing a neurotoxin called tetanospasmin. This neurotoxin blocks inhibitory signals in the central nervous system, leading to muscle spasms and stiffness characteristic of tetanus. Clostridium perfringens (B) causes gas gangrene, Streptococcus pyogenes (C) causes strep throat, and Escherichia coli (D) can cause gastrointestinal infections but not tetanus. Therefore, based on the specific pathogen and its mechanism of action, Clostridium tetani is the correct answer.

Correct Answer: D

Rationale: Step 1: Streptococcus pneumoniae is a common cause of community-acquired pneumonia. Step 2: Mycobacterium tuberculosis can lead to tuberculosis, which can manifest as pulmonary tuberculosis. Step 3: Escherichia coli is not typically associated with causing pneumonia. Step 4: Since Streptococcus pneumoniae and Mycobacterium tuberculosis are linked to pneumonia, and Escherichia coli is not, the correct answer is D - All of the above.

Correct Answer: A

Rationale: The correct answer is A: Trichomonads. Trichomonads are pear-shaped protozoa, typically 6-13 micrometers long, with one nucleus, undulating membrane, and four flagella at the front. These characteristics match the description provided in the question. Trichomonads are commonly found in oral cavities and can cause gum infections like periodontosis. Summary: - B: Leishmania - Leishmania is a flagellated protozoan responsible for Leishmaniasis, not typically found in the oral cavity. - C: Amoebae - Amoebae are not pear-shaped and do not have the specific characteristics described in the question. - D: Balantidia - Balantidia are ciliated protozoa, not flagellated like trichomonads, and are not typically associated with gum infections.

Correct Answer: C

Rationale: The correct answer is C: Clostridium perfringens. This bacterium is the causative agent of gas gangrene due to its ability to produce gas and toxins in anaerobic conditions. Clostridium tetani causes tetanus, Clostridium botulinum causes botulism, and Bacillus anthracis causes anthrax, not gas gangrene. Clostridium perfringens stands out as the correct choice based on its specific association with gas gangrene and its pathogenic mechanisms.

Correct Answer: A

Rationale: The correct answer is A: Neisseria meningitidis. This bacterium is a Gram-negative diplococcus, oxidase-positive, and fermentative. Neisseria meningitidis is known to cause respiratory infections and is commonly found in sputum cultures of patients with such infections. Neisseria gonorrhoeae (B) is also a Gram-negative diplococcus but is not fermentative. Moraxella catarrhalis (C) is oxidase-positive but not fermentative. Haemophilus influenzae (D) is not a diplococcus and is not fermentative. Therefore, Neisseria meningitidis is the most likely causative agent based on the given characteristics.

Correct Answer: B

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.

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: Syphilis. Hutchinson's triad is a classic presentation of congenital syphilis. Barrel-shaped teeth, parenchymatous keratitis, and deafness are hallmark signs. These occur due to infection of the fetus by the spirochete Treponema pallidum. Syphilis can lead to various systemic manifestations, including skeletal abnormalities, skin lesions, and neurological complications. Opisthorchiasis, Toxoplasmosis, and Tuberculosis do not typically present with the specific triad described in the question. Opisthorchiasis is a parasitic infection, Toxoplasmosis is caused by a protozoan, and Tuberculosis is a bacterial infection that primarily affects the lungs.

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.