medical microbiology test bank

Correct Answer: A

Rationale: The correct answer is A: Icosahedral structures. Icosahedral symmetry is commonly found in viruses due to its efficient way of packing genetic material. The icosahedron has 20 equilateral triangular faces, making it ideal for viral capsids. The other choices, B: Hexahedral, C: Tetrahedral, and D: Dodecahedral structures, do not accurately describe the cubic type of symmetry seen in viruses. Hexahedral refers to a six-faced polyhedron, tetrahedral to a four-faced polyhedron, and dodecahedral to a twelve-faced polyhedron, none of which align with the structure commonly observed in viruses.

Correct Answer: A

Rationale: The correct answer is A: chloroplasts. Algae and plant cells have chloroplasts, which are responsible for photosynthesis. This organelle contains chlorophyll, enabling these cells to convert sunlight into energy. Mitochondria (B) are found in all eukaryotic cells, not specific to algae and plants. Vacuoles (C) are present in plant cells but also in other eukaryotic cells. Vesicles (D) are membrane-bound sacs found in all types of cells for transport and storage purposes, not unique to algae and plants. Therefore, A is the correct answer.

Correct Answer: D

Rationale: The correct answer is D, "All of the above," because all three bacteria (Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus) can cause urinary tract infections. E. coli is the most common causative agent of UTIs, followed by Staphylococcus aureus and occasionally Pseudomonas aeruginosa. Each of these bacteria has different virulence factors that enable them to infect the urinary tract. Therefore, it is important to consider all three options when diagnosing and treating UTIs. Choices A, B, and C are incorrect because each of those bacteria can individually cause UTIs, so the correct answer is D, as it encompasses all the possible causative agents.

Correct Answer: D

Rationale: The bacitracin sensitivity test is used to differentiate between different types of streptococci. Group A streptococci are sensitive to bacitracin, which means they will show inhibition around the bacitracin disk. This sensitivity is a characteristic feature of group A streptococci and helps in their identification. Staphylococci, pneumococci, and intestinal bacteria do not exhibit this sensitivity to bacitracin. Therefore, the correct answer is D: group A streptococci.

Correct Answer: D

Rationale: The correct answer is D: Index of fecal coli-forms. Fecal coli-forms are bacteria found in the intestines of warm-blooded animals, including humans. Their presence in water indicates fecal contamination, which is a common source of hepatitis A transmission. Monitoring the index of fecal coli-forms can help identify potential sources of contamination and assess the risk of disease transmission. A: Number of coli-phages - Coli-phages are viruses that infect coliform bacteria and are not directly related to fecal contamination. B: Escherichia coli index - While E. coli is a type of coliform bacteria found in the intestines of warm-blooded animals, it alone may not be a reliable indicator of fecal contamination in water sources. C: Oxidability - Oxidability is a measure of the water's ability to react with oxygen and does not provide direct information about fecal contamination or the presence of pathogens like hepatitis A. In summary,