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Which of the following bacteria is known for causing the disease tetanus?
- A. Clostridium tetani
- B. Clostridium perfringens
- C. Streptococcus pyogenes
- D. Escherichia coli
Correct Answer: A
Rationale: The correct answer is A: Clostridium tetani. This bacterium is known for causing tetanus due to its ability to produce tetanospasmin, a neurotoxin that leads to the characteristic muscle stiffness and spasms seen in tetanus. Clostridium perfringens (Choice B) is associated with gas gangrene, Streptococcus pyogenes (Choice C) causes streptococcal infections, and Escherichia coli (Choice D) is known for causing various gastrointestinal infections. Therefore, Choices B, C, and D are incorrect as they are not the causative agents of tetanus.
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The time response measures all of the following except:
- A. ED50
- B. Peak effect time
- C. Onset of response
- D. Threshold level
Correct Answer: A
Rationale: The correct answer is A: ED50. The time response does not measure the ED50 because ED50 refers to the effective dose needed to produce a response in 50% of the population, which is a dose-related concept, not a time-related one. Peak effect time, onset of response, and threshold level are all time-related measures in pharmacology. Peak effect time is the time taken to reach the maximum response, onset of response is the time taken for the response to start, and threshold level is the minimum dose or concentration required to produce a response. Therefore, A is the correct answer as it is the only choice that is not a time-related measure in this context.
Formic acid is a fermentation product of
- A. Streptococcus.
- B. Klebsiella.
- C. Clostridium.
- D. Actinomyces.
Correct Answer: D
Rationale: Step 1: Formic acid is produced during fermentation by Actinomyces.
Step 2: Actinomyces are known to produce organic acids like formic acid through fermentation.
Step 3: Other choices like Streptococcus, Klebsiella, and Clostridium are not typically associated with formic acid production.
Step 4: Actinomyces is the most likely candidate based on its fermentation capabilities.
Summary: Actinomyces is the correct answer because it is known to produce formic acid during fermentation, while the other choices lack this specific metabolic function.
If skin-allergic samples for tuberculosis are negative:
- A. Antibiotics are prescribed
- B. Tuberculin is introduced
- C. A vaccine is administered
- D. None of the above
Correct Answer: B
Rationale: Step-by-step rationale for why choice B (Tuberculin is introduced) is correct:
1. Tuberculin test helps identify individuals with latent TB infection.
2. Negative skin-allergic samples suggest absence of active TB.
3. Introducing tuberculin can help confirm latent TB infection.
4. Antibiotics are not prescribed for negative skin-allergic samples.
5. Vaccines are not administered for TB diagnosis.
Summary:
- Choice A is incorrect as antibiotics are not prescribed for negative skin-allergic samples.
- Choice C is incorrect as vaccines are not used for TB diagnosis.
- Choice D is incorrect as introducing tuberculin is the appropriate step in this scenario.
The virulence factors of bacteria include:
- A. size, adhesion, resistance, and mutation
- B. colonization, invasion, toxins, and adhesion
- C. toxins, evasion of body defenses, motility, and size
- D. colonization, chemotaxis, fermentation, and toxins
Correct Answer: B
Rationale: Rationale: The correct answer is B because virulence factors of bacteria are characteristics that enable them to cause disease. Colonization allows bacteria to establish and multiply in the host. Invasion refers to the ability to penetrate host tissues. Toxins are substances produced by bacteria that harm the host. Adhesion is crucial for bacteria to attach to host cells.
A: Size and mutation are not typical virulence factors. Resistance is not directly related to causing disease.
C: While toxins and evasion of body defenses are correct, motility and size are not universally considered virulence factors.
D: Chemotaxis and fermentation are not primary virulence factors, unlike colonization and toxins.
A patient's sputum was stained using Ziehl-Neelsen method, which revealed red-colored bacilli on a blue background. What structural component of the cell is responsible for this staining property?
- A. Mycolic acid
- B. Capsule
- C. Flagella
- D. Endospores
Correct Answer: A
Rationale: The correct answer is A: Mycolic acid. Ziehl-Neelsen method is used to stain acid-fast bacteria, such as Mycobacterium species. Mycolic acid in the cell wall of these bacteria resists decolorization, leading to red-colored bacilli on a blue background. Capsule, flagella, and endospores do not play a role in this staining property. Capsules are usually stained using special techniques, flagella are not typically visible with this stain, and endospores are stained using the Schaeffer-Fulton method.