openstax microbiology test bank

Correct Answer: D

Rationale: The correct answer is D: thimerosal. Thimerosal is a mercury-containing compound used as a preservative in vaccines. It helps prevent contamination and growth of bacteria and fungi in multi-dose vials. Choice A, analgesic, refers to pain relievers, not preservatives. Choice B, EDTA, is a chelating agent used to bind metal ions and is not a preservative. Choice C, codeine, is an opioid pain medication and not a preservative used in vaccines. Thimerosal is the correct answer as it specifically fits the description of a mercury-containing compound used in vaccines.

Correct Answer: C

Rationale: The correct answer is C: Helicobacter pylori. Group I organisms are classified based on their low infectious doses and potential for bioterrorism. H. pylori is known to cause gastric ulcers and is categorized as a Group I organism due to its ability to cause disease at low doses. A: Francisella tularensis is a Group A bioterrorism agent, not Group I. B: Clostridium difficile is not typically classified as a Group I organism. D: Bacillus anthracis is a Group A bioterrorism agent, not Group I.

Correct Answer: A

Rationale: The correct answer is A: Escherichia coli. E. coli typically produces red colonies on Endo agar due to its ability to ferment lactose. This results in the production of acid, causing the colonies to appear red. Salmonella and Shigella are non-lactose fermenters, so they would appear colorless or transparent on Endo agar. Proteus vulgaris is not commonly associated with red colonies on Endo agar. Therefore, based on the characteristic lactose fermentation pattern, E. coli is the most likely microorganism in this scenario.

Correct Answer: B

Rationale: The correct answer is B: Pseudomonas aeruginosa. This bacterium is commonly associated with hospital-acquired infections due to its ability to survive in hospital environments, resist antibiotics, and infect immunocompromised patients. Streptococcus pneumoniae (choice A) is more commonly associated with community-acquired pneumonia. Vibrio cholerae (choice C) causes cholera, a waterborne disease, and is not typically associated with hospital-acquired infections. Choice D is incorrect because Pseudomonas aeruginosa is indeed associated with hospital-acquired infections.

Correct Answer: C

Rationale: Step 1: Chlorhexidine belongs to the group of biguanides, which are commonly used for disinfecting hands, skin, and mucous membranes. Step 2: It is known to have broad-spectrum antimicrobial activity against various pathogens. Step 3: The usage of chlorhexidine in healthcare settings for preoperative skin preparation and surgical hand scrub is well-established. Step 4: The effectiveness and safety profile of chlorhexidine make it a preferred choice for disinfection purposes. Summary: - Option A is incorrect as chlorhexidine is not characterized by strong human toxicity. - Option B is incorrect as chlorhexidine is not classified as an alcohol and is primarily used for disinfecting hands, skin, and mucous membranes. - Option D is incorrect as chlorhexidine has a wide range of applications in disinfection, especially in healthcare settings.