Nokea
Which bacteria are Gram-negative cocci?
- A. Neisseria species
- B. Streptococcus species
- C. Bacillus species
- D. Clostridium species
Correct Answer: A
Rationale: The correct answer is A: Neisseria species. Gram staining differentiates bacteria based on cell wall composition. Gram-negative bacteria like Neisseria have a thin peptidoglycan layer and an outer membrane, making them appear pink under the microscope. Streptococcus species (B) are Gram-positive cocci with a thick peptidoglycan layer, appearing purple. Bacillus (C) and Clostridium (D) species are Gram-positive rods, not Gram-negative cocci. Thus, the correct answer is A because Neisseria species are the only Gram-negative cocci among the choices provided.
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All statements of viral neutralization reaction are true except:
- A. A key component of the reaction is the complement system involvement
- B. Specific virus neutralising antibodies block the viral ability to infect cells
- C. The antibodies are titrated and two serum samples are required
- D. It is also used to identify newly isolated virus
Correct Answer: A
Rationale: Rationale:
A: Incorrect - The complement system is not directly involved in the viral neutralization reaction.
B: Correct - Specific antibodies neutralize viruses by blocking their ability to infect cells.
C: Incorrect - Antibodies are titrated, but only one serum sample is required for neutralization testing.
D: Incorrect - Viral neutralization is primarily used to measure antibody response, not to identify newly isolated viruses.
What is the structure of the bacterial cell wall?
- A. Peptidoglycan
- B. Lipopolysaccharides
- C. Phospholipids
- D. Chitin
Correct Answer: A
Rationale: The correct answer is A: Peptidoglycan. Bacterial cell walls are composed of peptidoglycan, a unique macromolecule consisting of sugars and amino acids. This structure provides rigidity and protection to the cell. Lipopolysaccharides are found in the outer membrane of Gram-negative bacteria, not in the cell wall. Phospholipids are the main components of cell membranes, not cell walls. Chitin is a structural polysaccharide found in the cell walls of fungi and some algae, not bacteria.
Which is NOT a property of interferon?
- A. Released from infected cells
- B. Acts extracellularly to inactivate virus
- C. Coded for by cellular DNA
- D. Not virus-specific but is cell-specific
Correct Answer: D
Rationale: Interferon is a cell-specific protein that is produced and released from infected cells in response to viral infections. It acts extracellularly to interfere with viral replication, not to inactivate the virus itself. Interferon is not coded for by cellular DNA, but by viral RNA during infection. Therefore, the correct answer, D, is that interferon is not virus-specific but is cell-specific. This is because interferon can be produced by various cell types in response to different types of viral infections, making it a broad-spectrum antiviral defense mechanism.
Which of the following bacteria is associated with the formation of dental caries?
- A. Streptococcus mutans
- B. Streptococcus pneumoniae
- C. Bacillus cereus
- D. Clostridium tetani
Correct Answer: A
Rationale: Step 1: Streptococcus mutans is known for its ability to produce lactic acid, which contributes to the demineralization of tooth enamel, leading to dental caries.
Step 2: Streptococcus pneumoniae is a common respiratory pathogen and not directly associated with dental caries.
Step 3: Bacillus cereus is a foodborne pathogen and not typically found in the oral cavity or associated with dental caries.
Step 4: Clostridium tetani causes tetanus, a neurological condition, and is not involved in the formation of dental caries.
Summary: Choice A is correct as Streptococcus mutans is specifically linked to dental caries due to its acidogenic and aciduric properties. Choices B, C, and D are incorrect as they are not associated with dental caries.
Which of the following viruses belongs to family Caliciviridae?
- A. Norwalk Virus
- B. Yellow fever virus
- C. Rubella virus
- D. CMV
Correct Answer: A
Rationale: The correct answer is A: Norwalk Virus. The Norwalk Virus belongs to the family Caliciviridae because it has characteristic features such as a nonenveloped, single-stranded RNA genome. The other options, Yellow fever virus, Rubella virus, and CMV, belong to different virus families and have distinct characteristics that differentiate them from Caliciviridae. Yellow fever virus is a Flavivirus, Rubella virus belongs to Togaviridae, and CMV is a member of the Herpesviridae family. Therefore, based on the genomic and structural characteristics of the Norwalk Virus, it is the correct choice for belonging to the Caliciviridae family.