Nokea
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.
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A fecal sample cultured on Endo agar revealed colorless colonies. The bacteria were Gram-negative rods and lactose non-fermenters. What microorganism is most likely?
- A. Salmonella
- B. Escherichia coli
- C. Shigella
- D. Proteus
Correct Answer: C
Rationale: The correct answer is Shigella (Choice C) because it matches the description of being Gram-negative rods and lactose non-fermenters. Shigella is a non-lactose fermenting, Gram-negative rod that typically produces colorless colonies on Endo agar. Salmonella (Choice A) and Escherichia coli (Choice B) are both lactose fermenters and would produce pink colonies on Endo agar. Proteus (Choice D) is also a lactose fermenter and would appear pink on Endo agar. Therefore, based on the characteristics provided, Shigella is the most likely microorganism in this scenario.
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.
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.
Salmonellosis is caused by:
- A. Salmonella typhi
- B. Salmonella enteritidis
- C. Shigella flexneri
- D. None of the above
Correct Answer: B
Rationale: The correct answer is B: Salmonella enteritidis. Salmonellosis is typically caused by Salmonella species, with Salmonella enteritidis being one of the common culprits. Salmonella typhi causes typhoid fever, not salmonellosis. Shigella flexneri is responsible for causing shigellosis, a different bacterial infection. Choosing "None of the above" is incorrect as Salmonella enteritidis is a known cause of salmonellosis.
Immunity after single vaccination against tetanus - application of tetanus toxoid is:
- A. intense and usually life long
- B. of limited duration, booster vaccinations are needed
- C. infectious (non-sterile)
- D. no correct answer
Correct Answer: B
Rationale: The correct answer is B. Immunity after a single tetanus vaccination is of limited duration, usually around 10 years. Booster vaccinations are needed to maintain protection due to waning immunity over time. Choice A is incorrect as immunity is not usually lifelong. Choice C is incorrect as tetanus toxoid is a sterile vaccine and does not cause infection. Choice D is also incorrect as there is a correct answer, which is B.