openstax microbiology test bank

Correct Answer: A

Rationale: The correct answer is A because spheroplasts are bacteria with defective cell walls that have a parietal layer (peptidoglycan layer) and a defective peptidoglycan layer. This is because spheroplasts have lost their rigid cell wall structure, leading to an incomplete peptidoglycan layer. Choice B is incorrect as the cytoplasmic membrane is not directly affected by the loss of cell wall integrity. Choice C is incorrect because spheroplasts do not have an outer membrane defect, but rather a defect in the peptidoglycan layer. Choice D is incorrect because spheroplasts still have peptidoglycan, even though it is defective.

Correct Answer: C

Rationale: The correct answer is C (100�C) because the Koch apparatus is used for sterilization, and the standard temperature for sterilization is 100�C. At this temperature, most microorganisms are killed, making it an effective method for sterilization. Choice A (90�C), B (95�C), and D (110�C) are incorrect because they are not commonly used temperatures for sterilization purposes. Choosing a temperature lower than 100�C may not effectively kill all microorganisms, while choosing a temperature higher than 100�C may lead to unnecessary energy consumption without providing additional sterilization benefits.

Correct Answer: B

Rationale: The correct answer is B: Clostridium tetani. This bacterium produces tetanospasmin toxin, causing tetanus. Clostridium botulinum (choice A) produces botulinum toxin, leading to botulism. Bacillus anthracis (choice C) causes anthrax, not tetanus. Staphylococcus aureus (choice D) can cause various infections, but not tetanus. Therefore, only Clostridium tetani is the causative agent of tetanus.

Correct Answer: C

Rationale: The correct answer is C: Erysipelas. Erysipelas is a type of acute infection caused by group A Streptococcus bacteria. This bacteria infects the upper dermis and superficial lymphatics, leading to a distinct raised, well-demarcated, erythematous skin lesion. The other choices are incorrect because: A Carbuncle is a deep skin infection involving hair follicles, B Impetigo is a superficial skin infection caused by Staphylococcus or Streptococcus bacteria, and D Acne is a chronic inflammatory skin condition not typically caused by group A Streptococcus.

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.