Nokea
Which of the following bacteria is capable of forming spores to survive in extreme conditions?
- A. Staphylococcus aureus
- B. Clostridium botulinum
- C. Escherichia coli
- D. Neisseria gonorrhoeae
Correct Answer: B
Rationale: The correct answer is B: Clostridium botulinum. This bacterium is capable of forming spores as a survival mechanism in harsh conditions. Spore formation allows it to remain dormant until conditions become favorable for growth again. Staphylococcus aureus (A), Escherichia coli (C), and Neisseria gonorrhoeae (D) do not form spores and rely on other mechanisms for survival. Staphylococcus aureus is a common skin bacterium, Escherichia coli is a gut bacterium, and Neisseria gonorrhoeae is a sexually transmitted bacterium.
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Which of the following statements is FALSE regarding B cells?
- A. B cells that recognize high concentrations of antigen (self) in the absence of other signals undergo apoptosis in the bone marrow
- B. Bone marrow stem cells migrate to the thymus and develop into B cells
- C. B cells synthesize antibodies and put them on their cell surface
- D. B cells can undergo class switching and produce a different antibody type
Correct Answer: B
Rationale: B cells develop in the bone marrow, not the thymus. Firstly, hematopoietic stem cells in the bone marrow give rise to B cells. They undergo maturation and selection processes in the bone marrow, not in the thymus. Therefore, choice B is false. On the other hand, choices A, C, and D are correct. A is true because B cells with high affinity to self-antigens undergo apoptosis to prevent autoimmunity. C is true since B cells synthesize antibodies which can be displayed on their surface as B cell receptors. D is true because B cells can undergo class switching to produce different types of antibodies based on the immune response requirements.
The causative agent of tuberculosis is:
- A. Mycobacterium leprae
- B. Mycobacterium tuberculosis
- C. Bacillus anthracis
- D. Staphylococcus aureus
Correct Answer: B
Rationale: The correct answer is B: Mycobacterium tuberculosis. Mycobacterium tuberculosis is the causative agent of tuberculosis, as it specifically infects the lungs and can spread to other parts of the body. Mycobacterium leprae (Choice A) causes leprosy, not tuberculosis. Bacillus anthracis (Choice C) causes anthrax, not tuberculosis. Staphylococcus aureus (Choice D) is a common bacterium known for causing skin infections, not tuberculosis. Therefore, Mycobacterium tuberculosis is the correct answer for the causative agent of tuberculosis.
Which of the following proteins are encoded by herpesviruses and required for viral DNA replication?
- A. viral DNA polymerase
- B. ribonucleotide reductase
- C. neuraminidase
- D. thymidine kinase
Correct Answer: A
Rationale: The correct answer is A: viral DNA polymerase. This enzyme is essential for replicating the viral DNA during the herpesvirus life cycle. It catalyzes the synthesis of new DNA strands using the viral genomic template. Ribonucleotide reductase (B) is involved in nucleotide synthesis, but not directly in DNA replication. Neuraminidase (C) is an enzyme found in influenza viruses, not herpesviruses. Thymidine kinase (D) is an enzyme that phosphorylates thymidine, but its role is more related to nucleotide metabolism rather than viral DNA replication.
Which form of human plague is present with high fever and large lymphadenopathies (buboes). The case fatality in untreated cases may reach 60%.
- A. Bubonic plague
- B. Pneumonic plague
- C. Gastrointestinal plague
- D. Septicemic plague
Correct Answer: A
Rationale: The correct answer is A: Bubonic plague. Bubonic plague is characterized by high fever and large swollen lymph nodes (buboes). The case fatality rate in untreated cases can reach 60%. This form of plague is typically transmitted through the bite of an infected flea.
B: Pneumonic plague presents with respiratory symptoms and is transmitted through respiratory droplets.
C: Gastrointestinal plague is not a recognized form of plague.
D: Septicemic plague is a severe form of plague where the bacteria multiply in the bloodstream. It may not always present with buboes.
Which of the following have a fecal oral route of transmission?
- A. Diphtheria
- B. Typhoid fever
- C. Syphilis
- D. Spotted fever
Correct Answer: B
Rationale: The correct answer is B: Typhoid fever. Typhoid fever is transmitted through the fecal-oral route, meaning the bacteria from an infected person's feces can contaminate food or water and then be ingested by another person. This can lead to infection and illness. The other choices, diphtheria (A), syphilis (C), and spotted fever (D) are not transmitted through the fecal-oral route. Diphtheria is spread through respiratory droplets, syphilis is primarily sexually transmitted, and spotted fever is transmitted through tick bites. Thus, only Typhoid fever aligns with the fecal-oral route of transmission.