Which of the following statements is accurate in explaining why gram-negative bacteria are generally more resistant to penicillin than gram-positive bacteria

Correct Answer: C

Rationale: The correct answer is C: gram-negative bacteria have an outer membrane that acts as an extra barrier. This outer membrane in gram-negative bacteria contains lipopolysaccharides and porins, which restrict the entry of antibiotics like penicillin. The outer membrane acts as an additional layer of protection, making it harder for penicillin to penetrate and reach its target, the peptidoglycan layer. Choices A, B, and D do not directly address the specific mechanism of resistance seen in gram-negative bacteria. Choice A focuses on transpeptidase enzyme quantity, which is not the primary reason for penicillin resistance. Choice B refers to β-lactamase enzymes in the periplasmic space, which are actually enzymes that degrade penicillin and contribute to resistance, but this is not unique to gram-negative bacteria. Choice D mentions a thicker cell wall, which is a characteristic of gram-positive bacteria, not gram-negative bacteria.

Correct Answer: C

Rationale: The correct answer is C: plasmids. Plasmids are nonchromosomal DNA molecules commonly found in bacterial cells, providing additional genetic material for bacteria. They are not essential for bacterial survival but can confer advantages such as antibiotic resistance. Endospores (A) are dormant bacterial structures resistant to harsh conditions. Transposons (B) are mobile genetic elements that can move within a genome. Prions (D) are misfolded proteins causing neurodegenerative diseases, not DNA molecules.

Correct Answer: A

Rationale: The correct answer is A: Microscopy of blood smears. Malaria diagnosis is confirmed by identifying the Plasmodium parasite in a blood smear. This step is crucial as it directly visualizes the causative agent. The other choices are incorrect as they do not directly detect malaria parasites. B: Studying lymph node punctate is not specific for malaria. C: Urinalysis does not show malaria parasites. D: Studying cerebrospinal fluid is used to diagnose conditions affecting the brain and spinal cord, not malaria.

Correct Answer: D

Rationale: The correct answer is D because a fourfold increase in titer in the second serum sample indicates a significant rise in specific antibodies, which is crucial for diagnosing viral infections accurately. This increase is considered significant in serologic reactions as it shows a strong antibody response to the virus. A: A threshold increase may not be substantial enough to confirm a diagnostic antibody response. B: Dismissing the increase in titer would overlook important diagnostic information. C: A twofold increase may not be as indicative of a strong antibody response compared to a fourfold increase.

Correct Answer: C

Rationale: The correct answer is C because chills, fever, and loss of consciousness are not typical symptoms of botulism. Botulism is characterized by descending, flaccid paralysis (choice A), dry mouth, difficulty swallowing, and speaking (choice B), and blurred vision, diplopia (choice D). These symptoms result from the neurotoxin produced by Clostridium botulinum, leading to muscle weakness and paralysis. Chills, fever, and loss of consciousness are more commonly associated with infections or other conditions, not botulism.

Correct Answer: A

Rationale: The correct answer is A: Leptospira. The key features pointing to Leptospira are the presence of convoluted bacteria resembling C and S letters, which is characteristic of Leptospira species. Leptospirosis presents with fever, jaundice, haemorrhagic rash, and acute renal insufficiency. The other choices (B: Treponema, C: Spirilla, D: Borrelia) do not match the histological description or the clinical presentation of the case. Treponema is associated with syphilis, Spirilla with genus Spirochaeta, and Borrelia with Lyme disease, none of which match the given scenario.

Correct Answer: A

Rationale: The correct answer is A: Complex. Poxviruses have a complex nucleocapsid symmetry due to their unique structure with multiple layers of proteins and genetic material. Isohedral symmetry (B) refers to a regular polyhedron shape, which is not characteristic of poxviruses. Helical symmetry (C) is found in viruses like tobacco mosaic virus, not poxviruses. "All of the above" (D) is incorrect because poxviruses do not exhibit isohedral or helical symmetry.

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: B

Rationale: The correct answer is B: mycorrhizae. Mycorrhizae are symbiotic fungi that form a mutualistic relationship with plant roots, aiding in the absorption of minerals and water. They enhance the plant's nutrient uptake capacity, promoting plant growth and health. Decomposers (A) break down dead organic matter, yeasts (C) are single-celled fungi used in fermentation, and molds (D) are fungi that grow in multicellular filaments. These options do not specifically assist plant roots in mineral and water absorption like mycorrhizae do.