Which bacteria are responsible for causing foodborne illnesses?

Correct Answer: D

Rationale: The correct answer is D, "All of the above," because all three bacteria (Salmonella enterica, Clostridium botulinum, Escherichia coli) are known to cause foodborne illnesses. Salmonella causes symptoms like diarrhea, fever, and abdominal cramps. Clostridium botulinum produces a toxin leading to botulism, a severe illness affecting the nervous system. Escherichia coli strains like E. coli O157:H7 can cause food poisoning with symptoms such as bloody diarrhea. Therefore, all the listed bacteria can cause foodborne illnesses due to their ability to contaminate food and infect individuals.

Correct Answer: D

Rationale: The correct answer is D because antibody diversity is generated by rearrangements of DNA encoding variable regions of heavy and light chains (choice A) and by the combination of different heavy and light chains that form the antigen binding site (choice B). Step 1: DNA rearrangements create different variable regions in heavy and light chains. Step 2: Combination of different heavy and light chains leads to unique antigen binding sites. Step 3: This diversity allows antibodies to bind to different epitopes on the same antigen. Step 4: Choice C is incorrect as antibodies do not physically change shape to bind different epitopes.

Correct Answer: B

Rationale: The correct answer is B: psittacosis. Psittacosis is an infection caused by Chlamydia psittaci that primarily affects the lower respiratory tract, leading to pneumonia-like symptoms. Mycoplasma pneumoniae causes atypical pneumonia, not pharyngitis (Choice A). Chronic atrophic rhinitis (Choice C) and rhinoscleroma (Choice D) both affect the upper respiratory tract, not the lower respiratory tract. Psittacosis specifically targets the lower respiratory tract, making it the most appropriate answer.

Correct Answer: C

Rationale: Correct Answer: C - Immunological tolerance to the pathogen Rationale: 1. Immunological tolerance is when the immune system does not mount a response against specific antigens to prevent autoimmunity. 2. In the context of infection, tolerance to the pathogen means the immune system does not recognize the pathogen as a threat and does not initiate a protective response. 3. This lack of response leaves the host vulnerable to infection as there is no specific immune defense mechanism activated against the pathogen. Summary of incorrect choices: A: Opsonic action of antibody - enhances phagocytosis of pathogens B: Viral neutralization by specific antibody - prevents viral entry into host cells D: Neutralization of protein exotoxin - prevents the harmful effects of toxins produced by pathogens.

Correct Answer: B

Rationale: The correct answer is B because a supercapsid is a lipoprotein membrane that encloses the nucleocapsid, providing protection to the genetic material inside. This structure is distinct from the capsid which is the protein coat surrounding the nucleic acid. Choice A is incorrect as there is no shell located between the capsid and supercapsid. Choice C is incorrect as it describes the nucleocapsid itself, not the supercapsid. Choice D is incorrect as a protein envelope around the nucleic acid does not specifically refer to a supercapsid.