What is the role of coagulase in bacteria like Staphylococcus aureus?

Correct Answer: C

Rationale: The correct answer is C because coagulase helps bacteria like Staphylococcus aureus to form clots, allowing them to evade the host immune response. This mechanism helps the bacteria to hide from the immune system and establish infection. A. Adhesion to surfaces is usually facilitated by other factors like adhesins. B. Breaking down red blood cells is not a function of coagulase. D. Antibiotic resistance is typically mediated by other mechanisms like efflux pumps or enzymatic inactivation, not coagulase.

Correct Answer: A

Rationale: Pili in bacteria are responsible for conjugation, allowing the transfer of genetic material between cells. They form a bridge between donor and recipient cells, facilitating the exchange of DNA. Flagella are for movement, capsules for protection, and ribosomes for protein synthesis. Pili is the only structure directly involved in genetic material exchange.

Correct Answer: A

Rationale: The correct answer is A: Borrelia burgdorferi. This bacterium is associated with Lyme disease, a tick-borne illness. Borrelia burgdorferi is transmitted to humans through the bite of infected black-legged ticks. It causes a range of symptoms, including fever, rash, joint pain, and neurological problems. Summary: B: Clostridium botulinum is associated with botulism, a serious illness caused by a toxin produced by this bacterium. C: Escherichia coli is a common bacterium found in the intestines of humans and animals, some strains can cause food poisoning. D: Streptococcus pneumoniae is a bacterium that can cause pneumonia and other respiratory infections, but not Lyme disease.

Correct Answer: C

Rationale: The correct answer is C: IgG. IgG is the only antibody that can cross the placenta due to its small size and unique structure, allowing it to provide passive immunity to the fetus. IgA is mainly found in mucosal secretions, IgM is too large to cross the placental barrier, and IgD plays a role in B cell activation but is not involved in placental transfer.

Correct Answer: A

Rationale: The correct answer is A: Break down antibiotics like penicillin. Beta-lactamase is an enzyme produced by bacteria to inactivate beta-lactam antibiotics like penicillin by breaking the beta-lactam ring. This mechanism helps bacteria resist the antibiotic's effects. The other choices are incorrect because beta-lactamase does not enhance protein synthesis, facilitate DNA replication, or transport nutrients. It specifically targets and deactivates beta-lactam antibiotics, making choice A the most appropriate answer.

Correct Answer: C

Rationale: The correct answer is C: 10% of the infected men have no symptoms. This is true because gonorrhea can be asymptomatic in some individuals, leading to undiagnosed cases. Testicular pain and epididymal tenderness (choice A) are not typical symptoms of gonorrhea in men. Painful urination (choice B) may or may not be present. Purulent discharge (choice D) is a common symptom but not always present. Therefore, choice C is the most accurate statement regarding gonorrhea symptoms in men.

Correct Answer: C

Rationale: The correct answer is C: Beta lactamase. This enzyme is produced by bacteria to break down the beta-lactam ring structure of penicillins, rendering them ineffective. Beta lactam ring (A) is part of the penicillin molecule, not an enzyme. MRSA (B) stands for methicillin-resistant Staphylococcus aureus, a type of bacteria resistant to certain antibiotics, not an enzyme. Aminoglycoside ring (D) refers to a different class of antibiotics and is not related to penicillin resistance in bacteria.

Correct Answer: B

Rationale: The correct answer is B because retroviruses, including those in the Family Retroviridae, have a capsid consisting of two copies of single-stranded RNA (ssRNA). This is a defining characteristic of retroviruses, which use reverse transcriptase to convert their ssRNA into DNA. This DNA is then integrated into the host cell's genome. Choices A, C, and D are incorrect because Family Retroviridae viruses are not helical non-enveloped viruses (C), they are not helical enveloped viruses (A), and they do not have a complex type of symmetry (D).

Correct Answer: A

Rationale: The correct answer is A: Lipopolysaccharides. Lipopolysaccharides (LPS) are major components of the outer membrane of Gram-negative bacteria and are known to have endotoxic activity. LPS can trigger a strong immune response leading to inflammation and septic shock. Choice B, Lipoproteins of Braun, are not known to have endotoxic activity. Choice C, Protein A, is a surface protein found in Staphylococcus aureus and is not associated with endotoxic activity. Choice D, None, is incorrect as LPS is indeed a bacterial structure with endotoxic activity.