Which of the following organisms produces toxins that target cholesterol?

Correct Answer: C

Rationale: Step 1: Escherichia coli is known to produce a toxin called colibactin that targets cholesterol. Step 2: Colibactin disrupts cholesterol metabolism in host cells. Step 3: This disruption can lead to various health issues. Step 4: Streptococcus pyogenes produces different toxins, not specifically targeting cholesterol. Step 5: Corynebacterium diphtheriae produces diphtheria toxin, not targeting cholesterol. Step 6: Aeromonas hydrophila produces various toxins, but not known for targeting cholesterol. Summary: Escherichia coli produces toxins that specifically target cholesterol, making it the correct choice over the other options.

Correct Answer: C

Rationale: The correct answer is C: Direct flaming. Direct flaming is the simplest heat-related method to sterilize metal because it involves passing the metal through a flame to kill microorganisms. The high temperature of the flame effectively destroys any bacteria or spores present on the metal surface. Incineration (A) is not practical for sterilizing metal as it involves burning at extremely high temperatures. Autoclaving (B) uses steam under pressure to sterilize, which is effective but more complex than direct flaming. Indirect heating (D) is not an effective method for sterilizing metal as it does not directly expose the metal to high temperatures required for sterilization.

Correct Answer: A

Rationale: The correct answer is A: Mononuclears, T-lymphocytes and lymphokines. In a Mantoux test reaction, mononuclear cells, mainly T-lymphocytes, are activated by the injected allergen. These T-lymphocytes release lymphokines, leading to the observed swelling, hyperaemia, and tenderness. Granulocytes and IgG (choice B) are not the primary players in this type of delayed hypersensitivity reaction. Plasmatic cells (choice C) are not involved in the initial stages of this reaction. B-lymphocytes and IgM (choice D) are not the key components in the Mantoux test reaction.

Correct Answer: A

Rationale: The correct answer is A: Cytopathic effect. This is because polioviruses cause visible changes in infected cells, leading to cell damage and death, known as cytopathic effect. This is a key characteristic of viral infection. Choice B (Cytotoxic effect) is incorrect as it refers to the toxicity of a substance to cells, not the specific effect of polioviruses. Choice C (Cytolytic effect) is incorrect as it specifically refers to cell lysis, which is not the primary mechanism of poliovirus infection. Choice D (They Don't Change The Cell Cultures) is incorrect because polioviruses do indeed cause changes in cell cultures due to their cytopathic effect.

Correct Answer: B

Rationale: The correct answer is B: Azotobacter species. Azotobacter are known for their ability to fix nitrogen through the process of nitrogen fixation, converting atmospheric nitrogen into a form that plants can use. Bacillus cereus is not known for nitrogen fixation. Clostridium botulinum is a bacterium that causes botulism and does not fix nitrogen. Escherichia coli is a common gut bacterium but does not have the ability to fix nitrogen. Thus, Azotobacter species is the correct choice based on its unique ability to fix nitrogen.

Correct Answer: D

Rationale: The correct answer is D: iatrogenic infections. Iatrogenic infections refer to infections caused by medical or surgical treatment, including procedures that introduce microorganisms into the body. In this case, infections of the reproductive tract caused by medical procedures fall under this category. A: Chronic infections do not specifically refer to infections caused by medical procedures. B: Endogenous infections arise from organisms already present in or on the body, not introduced through medical procedures. C: Systemic infections affect the entire body, not specific to infections caused by medical procedures. Therefore, the term "iatrogenic infections" is the most appropriate choice in this context.

Correct Answer: A

Rationale: Correct Answer: A Rationale: 1. Enteropathogenic E. coli (EPEC) attach to enterocytes via a type III secretion system. 2. Once attached, they form attaching and effacing lesions on the microvilli, leading to microvillus destruction. 3. This mechanism allows EPEC to cause diarrhea by disrupting the normal absorptive function of the intestines. Summary: - B (They are invasive and produce enterotoxin) is incorrect because EPEC are non-invasive and do not produce enterotoxins. - C (Cause disease clinically similar to bacterial) is vague and does not provide specific information about EPEC pathogenesis. - D (None of the above) is incorrect as A is the correct explanation for EPEC pathogenicity.

Correct Answer: A

Rationale: The correct answer is A: Nucleoid. The bacterial genome is located in the nucleoid, a region within the bacterial cell where the genetic material is condensed and organized. This structure is not the same as a nucleus found in eukaryotic cells. The other choices (B: Nucleotide and C: ATP) are incorrect because nucleotide refers to a building block of DNA or RNA, and ATP is a molecule used for energy transfer in cells, neither of which specifically houses the bacterial genome. Choice D: None of the above is incorrect as well, as the correct term for the compact structure containing the bacterial genome is the nucleoid.

Correct Answer: A

Rationale: The correct answer is A: Staphylococcus epidermidis. The presence of Gram-positive cocci in clusters, catalase-positive, and coagulase-negative characteristics indicate Staphylococcus species. Specifically, Staphylococcus epidermidis is a common skin commensal and a frequent cause of wound infections. Staphylococcus aureus is catalase-positive and coagulase-positive, making it less likely in this scenario. Streptococcus pyogenes and Enterococcus faecalis are both Gram-positive cocci but are catalase-negative, making them less likely causative agents.