F pili:

Correct Answer: C

Rationale: The correct answer is C because F pili are proteins on the F+ donor cell that are attached to specific receptors on the recipient cell's cell wall. This is essential for the transfer of genetic material during conjugation. Choice A is incorrect because F pili are not made up of nucleotides, but rather proteins. Choice B is incorrect because F pili are not transferred to the recipient cell itself, but they facilitate the transfer of genetic material. Choice D is incorrect because F pili are not part of the recipient cell, but rather part of the donor cell for attachment to the recipient cell.

Correct Answer: C

Rationale: The correct answer is C: halophiles. Halophiles are bacteria that thrive in high salt concentrations due to their ability to regulate osmotic pressure. They have adapted mechanisms to survive in such extreme environments. Option A, acidophiles, thrive in acidic conditions, not high salt concentrations. Option B, thermophiles, thrive in high temperature environments. Option D, mesophiles, thrive in moderate temperature conditions, not necessarily high salt concentrations. Therefore, the correct choice is C as it specifically refers to bacteria that thrive in high salt concentrations.

Correct Answer: B

Rationale: The correct answer is B: Mycobacterium tuberculosis. This bacterium is responsible for causing tuberculosis. Mycobacterium tuberculosis specifically targets the lungs, leading to respiratory symptoms and can spread to other parts of the body. Streptococcus pneumoniae (A) is known for causing pneumonia, Neisseria meningitidis (C) causes meningitis, and Clostridium botulinum (D) causes botulism, not tuberculosis. Mycobacterium tuberculosis is the only bacterium among the choices that is associated with tuberculosis.

Correct Answer: C

Rationale: The correct answer is C because there is no obligatory vaccine for Neisseria meningitidis in Bulgaria. The rationale for this is that while vaccines are available for meningococcal disease, they are not mandatory in Bulgaria. Therefore, this statement is incorrect. A: This statement is correct as Waterhouse-Friderichsen syndrome can occur during meningococcemia due to rapid progression of the infection leading to adrenal gland failure. B: This statement is incorrect as Neisseria meningitidis is most common in infants, children, and adolescents, with a second peak in young adults. D: This statement is correct as Neisseria meningitidis is transmitted through respiratory secretions, such as coughing or kissing, especially in close contacts like household members or roommates.

Correct Answer: B

Rationale: The correct answer is B: FALSE. Adenoviral infections are not restricted only to the upper respiratory tract; they can also affect the gastrointestinal tract, eyes, and other organs. Adenoviruses are known to cause a wide range of illnesses beyond just respiratory infections. Therefore, option B is correct. Option A is incorrect because it states that adenoviral infections are restricted to the upper respiratory tract, which is not true. Option C is incorrect because there is no circumstance where adenoviral infections are solely limited to the upper respiratory tract. Option D is also incorrect as the correct answer is B.

Correct Answer: A

Rationale: Step-by-step rationale for the correct answer (A: Epstein-Barr virus): 1. Epstein-Barr virus is a member of the Herpesviridae family, known for causing infectious mononucleosis. 2. Members of Herpesviridae have double-stranded DNA genomes and enveloped virions. 3. They establish latent infections in host cells and can reactivate periodically. 4. Poxvirus (B) belongs to the Poxviridae family, not Herpesviridae. 5. SARS (C) is caused by a coronavirus, not a herpesvirus. 6. HIV (D) belongs to the Retroviridae family, not Herpesviridae. Summary: The correct answer is A because Epstein-Barr virus is a member of the Herpesviridae family, exhibiting specific characteristics distinct from the other choices.

Correct Answer: C

Rationale: The correct answer is C: flagella. Flagella are whip-like structures that move fluid, mucus, or cells over the surface of a cell. They are longer and fewer in number compared to cilia, which are shorter and more numerous. Fimbriae are small, bristle-like structures that help bacteria attach to surfaces but do not move fluid. Microvilli are tiny projections that increase the surface area for absorption but do not have a role in moving fluid or cells. Therefore, flagella is the correct answer as it specifically fits the function described in the question.

Correct Answer: A

Rationale: The correct answer is A: virulence. Virulence refers to the degree or extent of disease-evoking power that a microorganism possesses. This term specifically describes the ability of a microorganism to cause disease in a host. It is a crucial factor in understanding the pathogenicity of different microorganisms. Choice B: strength is incorrect because it does not specifically relate to the disease-causing potential of a microorganism. Choice C: resistance refers to the ability of an organism to withstand the effects of a particular agent, such as a drug or environmental factor. Choice D: competence is not directly related to the disease-causing ability of a microorganism, but rather refers to the ability of an organism to perform a specific function effectively.

Correct Answer: D

Rationale: The correct answer is D: Ancylostoma duodenale. A scolex is a structure found in tapeworms, not in the other options which are roundworms. Ancylostoma duodenale is a species of hookworm, a type of intestinal parasite that has a distinct scolex with hook-like mouthparts for attachment to the host's intestinal wall. Enterobius vermicularis is a pinworm, Necator americanus is a hookworm species without a scolex, and Ascaris lumbricoides is a roundworm with a cylindrical body lacking a scolex. Therefore, the presence of a scolex specifically points to Ancylostoma duodenale.