Nokea
Which of the following does NOT refer to viruses
- A. cell-free infectious living systems
- B. obligate intracellular parasites
- C. they have either DNA or RNA as genetic material
- D. they are not sensitive to interferon
Correct Answer: D
Rationale: The correct answer is D because viruses are sensitive to interferon, a natural defense mechanism of the body against viral infections. Interferon helps to inhibit viral replication.
A: Viruses are cell-free infectious particles, not living systems.
B: Viruses are obligate intracellular parasites as they require host cells to replicate.
C: Viruses can have either DNA or RNA as genetic material, which is a characteristic feature.
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Which bacterium is known for producing an exotoxin that causes severe diarrhea?
- A. Clostridium tetani
- B. Clostridium botulinum
- C. Vibrio cholerae
- D. Shigella dysenteriae
Correct Answer: C
Rationale: Rationale:
1. Vibrio cholerae produces cholera toxin causing severe diarrhea.
2. Clostridium tetani causes tetanus, not diarrhea.
3. Clostridium botulinum causes botulism, not diarrhea.
4. Shigella dysenteriae causes dysentery, not typical diarrhea.
Summary:
A: Incorrect, causes tetanus.
B: Incorrect, causes botulism.
C: Correct, produces cholera toxin causing severe diarrhea.
D: Incorrect, causes dysentery.
Which of the following bacteria is known for causing dental caries (cavities)?
- A. Streptococcus mutans
- B. Streptococcus pneumoniae
- C. Bacillus anthracis
- D. Clostridium botulinum
Correct Answer: A
Rationale: Step 1: Streptococcus mutans is known for its ability to produce acids that contribute to the demineralization of tooth enamel, leading to dental caries.
Step 2: Streptococcus pneumoniae is a common cause of respiratory infections, not dental caries.
Step 3: Bacillus anthracis causes anthrax, a serious bacterial infection, not dental caries.
Step 4: Clostridium botulinum causes botulism, a severe form of food poisoning, not dental caries.
Summary: Streptococcus mutans is the correct answer as it is specifically associated with causing dental caries, while the other choices are linked to different diseases.
A 16-year-old adolescent was vaccinated with DTP. In eight days there was stiffness and pain in the joints, subfebrile temperature, urticarial skin eruption, enlargement of inguinal, cervical lymph nodes and spleen. What kind of allergic reaction is observed?
- A. Immunocomplex
- B. Hypersensitivity of immediate type
- C. Cytoxic
- D. Hypersensitivity of delayed type
Correct Answer: D
Rationale: The correct answer is D: Hypersensitivity of delayed type. The symptoms described occur 5-10 days after exposure to the antigen, consistent with a delayed hypersensitivity reaction. This type of reaction involves T cells and is characterized by cell-mediated immune response, leading to inflammation and tissue damage. Choices A, B, and C are incorrect because they are associated with different mechanisms of allergic reactions. Immunocomplex reactions (choice A) involve antigen-antibody complexes depositing in tissues, immediate hypersensitivity reactions (choice B) involve IgE-mediated mast cell degranulation, and cytotoxic reactions (choice C) involve antibodies targeting specific cells for destruction.
Which of the following bacteria produces a toxin that causes botulism?
- A. Clostridium botulinum
- B. Clostridium tetani
- C. Staphylococcus aureus
- D. Escherichia coli
Correct Answer: A
Rationale: The correct answer is A: Clostridium botulinum. Clostridium botulinum produces the botulinum toxin, which causes botulism. This bacteria thrives in anaerobic environments and can contaminate improperly canned foods. Clostridium tetani causes tetanus, not botulism. Staphylococcus aureus produces enterotoxins causing food poisoning, not botulism. Escherichia coli can cause food poisoning through various toxins, but not botulism. Therefore, the correct choice is Clostridium botulinum as it specifically produces the botulinum toxin responsible for botulism.
During the skill-building session in microbiology the students need to stain the prepared and fixed sputum smears obtained from a tuberculosis patient. What staining technique should be used in this case?
- A. Gram
- B. Giemsa
- C. Ziehl-Neelsen
- D. Burry
Correct Answer: C
Rationale: The correct staining technique for staining sputum smears from a tuberculosis patient is Ziehl-Neelsen staining. This technique uses a carbol fuchsin stain that specifically stains acid-fast organisms like Mycobacterium tuberculosis. The steps involved include staining with carbol fuchsin, decolorizing with acid-alcohol, counterstaining with methylene blue, and then examining under a microscope. This staining method is crucial for detecting the acid-fast bacilli characteristic of tuberculosis.
Explanation for incorrect choices:
A: Gram staining is used to differentiate bacteria into Gram-positive and Gram-negative, not suitable for acid-fast organisms like Mycobacterium tuberculosis.
B: Giemsa staining is used for detecting parasites and certain types of white blood cells, not specific for acid-fast bacteria.
D: Burry staining is not a recognized staining technique in microbiology for staining acid-fast organisms.