A patient with skin mycosis has disorder of cellular immunity. The most typical characteristic of it is reduction of the following index:

Correct Answer: A

Rationale: The correct answer is A: T-lymphocytes. In skin mycosis, a disorder of cellular immunity indicates a deficiency in T-lymphocytes, which play a crucial role in cell-mediated immunity. T-lymphocytes are responsible for recognizing and destroying infected cells. Reduction in T-lymphocytes impairs the body's ability to fight fungal infections. Incorrect choices: B: Immunoglobulin G - Immunoglobulin G is involved in humoral immunity, not cellular immunity. C: Immunoglobulin E - Immunoglobulin E is typically associated with allergic responses, not cellular immunity. D: B-lymphocytes - B-lymphocytes are responsible for producing antibodies in humoral immunity, not directly involved in cell-mediated immunity.

Correct Answer: D

Rationale: The correct answer is D: Hyaluronidase synthesis. Hyaluronidase is an enzyme produced by some pathogens to break down hyaluronic acid in the extracellular matrix, aiding their spread. This action does not directly counteract the immune system's mechanisms. Antigenic heterogeneity and mimicry can evade immune recognition. IgA proteases degrade IgA antibodies, impairing mucosal immunity. Therefore, D is the only choice not directly involved in counteracting the immune system.

Correct Answer: B

Rationale: Facultative anaerobes can switch between aerobic and anaerobic metabolism based on oxygen availability. This flexibility enables them to grow in both oxygen-rich and oxygen-poor environments, making choice B correct. Choice A is incorrect because facultative anaerobes do not require oxygen for survival. Choice C is incorrect as obligate anaerobes cannot grow in the presence of oxygen. Choice D is incorrect because obligate anaerobes cannot tolerate any amount of oxygen.

Correct Answer: A

Rationale: The correct answer is A: Artificial food media. Treponema pallidum is a fastidious bacterium that cannot be cultivated on artificial food media due to its complex nutritional requirements. It can be cultivated on cell lines and intratesticular in rabbits. Therefore, option A is incorrect. Option B and C are correct.

Correct Answer: D

Rationale: The correct answer is D: All of the above. Clostridium tetani, Staphylococcus aureus, and Escherichia coli are all capable of producing exotoxins. Exotoxins are proteins released by bacteria that can cause damage to the host. Clostridium tetani produces tetanospasmin, causing tetanus. Staphylococcus aureus produces toxins like enterotoxin and toxic shock syndrome toxin-1. Escherichia coli can produce Shiga toxin and heat-labile toxin. Therefore, all three bacteria listed can produce exotoxins, making choice D the correct answer. Choices A, B, and C are incorrect as they do not encompass all the bacteria capable of producing exotoxins.

Correct Answer: A

Rationale: The correct answer is A: Transformation. During transformation, bacteria take up foreign DNA from the environment and incorporate it into their own genetic material. This process allows for genetic diversity and adaptation. Transduction (B) involves transfer of DNA via a virus, conjugation (C) involves direct transfer of DNA between bacterial cells, and binary fission (D) is a form of asexual reproduction in bacteria. Transformation is the only process specifically related to bacteria taking up foreign DNA.

Correct Answer: C

Rationale: The correct answer is C: RNA-dependent RNA polymerase. This enzyme is required for replicating viral RNA due to its ability to catalyze the synthesis of RNA using an RNA template. Reverse transcriptase (A) is used to transcribe RNA into DNA, not replicate viral RNA. DNA polymerase (B) is used for replicating DNA, not RNA. Ligase (D) is involved in joining DNA fragments, not in replicating viral RNA. Therefore, RNA-dependent RNA polymerase is the only enzyme that specifically performs the function required for replicating viral RNA.

Correct Answer: A

Rationale: The correct answer is A: Lice. Lice, specifically body lice (Pediculus humanus corporis), are known carriers of the pathogen Rickettsia prowazekii, which causes epidemic typhus. Body lice are commonly found in unsanitary conditions and can transmit the bacteria through their bites. Spiders (choice B), bed-bugs (choice C), and cockroaches (choice D) are not known vectors of epidemic typhus. Spiders are predators that do not transmit diseases to humans, while bed-bugs and cockroaches are associated with other health issues but not epidemic typhus transmission.

Correct Answer: B

Rationale: The correct answer is B: It causes epidemic meningitis. Neisseria Meningitidis is a bacterium that can cause meningitis, an infection of the protective membranes covering the brain and spinal cord. This bacterium is known to cause outbreaks or epidemics of meningitis, especially in crowded or close-contact settings. The other choices are incorrect because: A: Neisseria Meningitidis does have a capsule, which helps it evade the immune system. C: Neisseria Meningitidis grows on selective media like Thayer-Martin agar, not differential media. D: Neisseria Meningitidis is a Gram-negative diplococcus, not a Gram-positive rod.