Which of the following bacteria is associated with the formation of dental caries?

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.

Correct Answer: D

Rationale: The correct answer is D: PCR. PCR (Polymerase Chain Reaction) is the most suitable method for detecting genitourinary chlamydiosis due to its high sensitivity and specificity in detecting the genetic material of Chlamydia trachomatis. PCR can detect even low levels of the pathogen, providing accurate results. A: Cultural diagnostic is not as sensitive as PCR and may take longer to produce results. B: ELISA detects antibodies, which may not be present in early stages of infection, leading to false-negative results. C: CFT (Complement Fixation Test) is an older method with lower sensitivity compared to PCR for detecting chlamydiosis.

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.

Correct Answer: D

Rationale: The correct answer is D, as all options A, B, and C are determinants of antigenicity. A: Chemical nature influences how the immune system recognizes antigens. B: The size of the antigen affects its ability to be recognized by immune cells. C: Antigens of foreign origin are more likely to trigger an immune response. Therefore, all of these factors together play a crucial role in determining antigenicity.

Correct Answer: A

Rationale: Acyclovir is the correct answer because it is an antiviral drug used to treat herpes simplex and varicella-zoster viruses, not influenza. Tamiflu, Amantadine, and Relenza are used to treat influenza by inhibiting viral replication or easing symptoms. Acyclovir's mechanism of action targets different viruses, making it ineffective for treating influenza.