openstax microbiology test bank

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A patient with an abscess had Gram-positive cocci in clusters isolated from a wound culture. The organism was catalase-positive and coagulase-positive. What is the likely causative agent?

  • A. Staphylococcus aureus
  • B. Staphylococcus epidermidis
  • C. Streptococcus pyogenes
  • D. Enterococcus faecalis
Correct Answer: A

Rationale: Step-by-step rationale:
1. Gram-positive cocci in clusters suggest Staphylococcus or Streptococcus.
2. Catalase-positive and coagulase-positive narrow it down to Staphylococcus.
3. Staphylococcus aureus is catalase-positive and coagulase-positive.
Therefore, the likely causative agent is Staphylococcus aureus.

Summary:
A: Correct - Staphylococcus aureus fits all the characteristics.
B: Incorrect - Staphylococcus epidermidis is catalase-negative and coagulase-negative.
C: Incorrect - Streptococcus pyogenes is catalase-negative and coagulase-negative.
D: Incorrect - Enterococcus faecalis is catalase-negative and coagulase-negative.

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Which of the following is a type of acute infection generally caused by group A Streptococcus?

  • A. Carbuncle
  • B. Impetigo
  • C. Erysipelas
  • D. Acne
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.

Tularemia is caused by

  • A. Francisella tularensis
  • B. Bordetella pertussis
  • C. Brucella suis
  • D. Legionella sp.
Correct Answer: A

Rationale: Step-by-step rationale:
1. Tularemia is caused by Francisella tularensis, a highly infectious bacterium.
2. Francisella tularensis is the only pathogen specifically known to cause tularemia.
3. The other choices (Bordetella pertussis, Brucella suis, Legionella sp.) are not associated with tularemia.
4. Therefore, the correct answer is A - Francisella tularensis.

The technique that combines freezing and drying to preserve microbes and other cells is

  • A. desiccation.
  • B. lyophilization.
  • C. pasteurization.
  • D. radiation.
Correct Answer: B

Rationale: The correct answer is B: lyophilization. This technique involves freezing the sample and then removing the ice through sublimation, preserving the cells in a dry state. Desiccation (A) simply involves drying without freezing. Pasteurization (C) is a heat treatment to kill pathogens, not used for preservation. Radiation (D) can sterilize but doesn't involve freezing and drying like lyophilization.

Which of the following organisms belongs in the group I category?

  • A. Francisella tularensis
  • B. Clostridium difficile
  • C. Helicobacter pylori
  • D. Bacillus anthracis
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.

A patient with a wound infection had a Gram-positive cocci isolated from the sample. The bacteria were catalase-positive and coagulase-positive. What is the most likely causative agent?

  • A. Staphylococcus aureus
  • B. Staphylococcus epidermidis
  • C. Streptococcus pyogenes
  • D. Enterococcus faecalis
Correct Answer: A

Rationale: The correct answer is A: Staphylococcus aureus. Staphylococcus aureus is a Gram-positive cocci that is catalase-positive and coagulase-positive, making it the most likely causative agent for the wound infection. Catalase-positive bacteria produce the enzyme catalase, which helps break down hydrogen peroxide. Coagulase-positive bacteria produce the enzyme coagulase, which causes the plasma proteins to clot. Staphylococcus epidermidis is catalase-positive but coagulase-negative, making it less likely to cause a wound infection. Streptococcus pyogenes is catalase-negative, and Enterococcus faecalis is catalase-negative and coagulase-negative, so they are less likely to be the causative agent.

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