Microscopic examination of a smear from a chancre revealed spiral microorganisms. The bacteria were thin and mobile with 8-12 regular coils. What is the likely diagnosis?

Correct Answer: A

Rationale: The correct diagnosis is A: Syphilis. The spiral microorganisms described are characteristic of Treponema pallidum, the causative agent of syphilis. The thin and mobile bacteria with 8-12 regular coils match the morphology of Treponema pallidum. Leptospirosis is caused by Leptospira interrogans, which are thicker and have hook-like ends, different from the described bacteria. Lyme disease is caused by Borrelia burgdorferi, which has a different appearance than the thin, coiled bacteria in the smear. Relapsing fever is caused by Borrelia recurrentis, which typically have irregular coils, unlike the regular coils seen in the smear.

Correct Answer: A

Rationale: Rationale: 1. Corynebacterium diphtheriae is the correct answer as it is the bacteria responsible for causing diphtheria, characterized by a thick pseudomembrane in the throat. 2. Streptococcus pyogenes causes strep throat but does not produce a pseudomembrane. 3. Neisseria meningitidis causes meningitis and septicemia, not a throat pseudomembrane. 4. Bacillus cereus causes food poisoning, not throat-related symptoms.

Correct Answer: B

Rationale: The correct answer is B: Helicobacter pylori. This bacterium is associated with stomach ulcers as it can survive in the acidic environment of the stomach and produce substances that weaken the stomach lining. Escherichia coli (A) is associated with foodborne illnesses, not ulcers. Bacillus cereus (C) causes food poisoning. Clostridium difficile (D) is associated with antibiotic-associated colitis, not ulcers. Therefore, Helicobacter pylori is the correct answer based on its specific association with stomach ulcers.

Correct Answer: B

Rationale: The correct answer is B: Yersinia pestis. Y. pestis is the causative agent of plague, a serious infectious disease transmitted through fleas. It causes bubonic, pneumonic, and septicemic plague. Bordetella pertussis causes whooping cough, Rickettsia prowazekii causes epidemic typhus, and Treponema pallidum causes syphilis. Y. pestis is the correct answer because it is specifically associated with plague, making the other options incorrect.

Correct Answer: B

Rationale: The correct answer is B: Catalase. Catalase is the enzyme responsible for breaking down hydrogen peroxide into water and oxygen. This process helps protect the bacteria from oxidative damage caused by hydrogen peroxide. Amylase (A), Lipase (C), and Protease (D) are enzymes that are not involved in breaking down hydrogen peroxide. Amylase is involved in breaking down starch, Lipase breaks down lipids, and Protease breaks down proteins. Therefore, they are not the correct enzymes for the given question.