openstax microbiology test bank

Correct Answer: A

Rationale: The correct answer is A: Streptococcus pyogenes. This is because Streptococcus pyogenes is a Gram-positive cocci in chains bacterium that is catalase-negative, making it the most likely causative agent in this scenario. Streptococcus pyogenes is a common pathogen causing bacterial endocarditis. Summary of other choices: B: Staphylococcus aureus is a Gram-positive cocci bacterium but is catalase-positive, so it is unlikely in this case. C: Enterococcus faecalis is a Gram-positive cocci bacterium, but it is catalase-negative, which is not consistent with the given information. D: Micrococcus luteus is a Gram-positive cocci bacterium but is catalase-positive, making it an unlikely causative agent.

Correct Answer: A

Rationale: The correct answer is A: Norwalk Virus. The Norwalk Virus belongs to the family Caliciviridae because it has characteristic features such as a nonenveloped, single-stranded RNA genome. The other options, Yellow fever virus, Rubella virus, and CMV, belong to different virus families and have distinct characteristics that differentiate them from Caliciviridae. Yellow fever virus is a Flavivirus, Rubella virus belongs to Togaviridae, and CMV is a member of the Herpesviridae family. Therefore, based on the genomic and structural characteristics of the Norwalk Virus, it is the correct choice for belonging to the Caliciviridae family.

Correct Answer: D

Rationale: The correct answer is D: All of the above. Streptococcus pneumoniae, Mycobacterium tuberculosis, and Escherichia coli can all cause pneumonia, but through different mechanisms. S. pneumoniae is a common cause of community-acquired pneumonia, M. tuberculosis can lead to tuberculosis-related pneumonia, and E. coli can cause pneumonia in immunocompromised individuals. Therefore, all three bacteria can be responsible for causing pneumonia, making option D the correct choice. Option A, Streptococcus pneumoniae, is correct but does not cover all possible causes of pneumonia. Option B, Mycobacterium tuberculosis, is too specific and does not include other common causes. Option C, Escherichia coli, is also a possible cause of pneumonia but does not account for all potential pathogens.

Correct Answer: A

Rationale: The correct answer is A: 4 and 250. Coli index is calculated by dividing the number of red colonies by the volume of water analyzed, which gives 2 red colonies / 500 ml = 4. Coli titer is the reciprocal of the coli index, so it is 1 / 4 = 250. This indicates the concentration of coliform bacteria in the water sample. Choices B, C, and D are incorrect as they do not follow the correct calculation steps for determining the coli index and coli titer. B has the correct coli index but incorrect coli titer. C and D have the values reversed, leading to incorrect results.

Correct Answer: C

Rationale: The correct answer is C: Peptidoglycan. Bacterial cell walls are primarily composed of peptidoglycan, a unique molecule consisting of alternating sugar chains connected by peptide cross-links. This structure provides rigidity and shape to the cell wall, protecting the bacterial cell from osmotic pressure. Lipopolysaccharides (A) are found in the outer membrane of Gram-negative bacteria. Cellulose (B) is a component of plant cell walls, not bacterial cell walls. Chitin (D) is a polysaccharide found in the exoskeletons of arthropods and fungi, not in bacterial cell walls.