Microbiology An Introduction Tortora Test Bank

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A 43-year-old cattle farm worker is brought to the surgeon with fever, malaise, and inflamed lesions on his hands and arms. He reports that about 2 weeks before his presentation at the hospital he noticed small, painless, pruritic papules that quickly enlarged and developed a central vesicle. The vesicles developed into erosion and left painless necrotic ulcers with black, depressed eschar. Gram's staining of the ulcer reveals gram-positive spore-forming bacilli. Which of the following diseases is the most likely cause of these findings?

  • A. Anthrax
  • B. Chickenpox
  • C. Syphilis
  • D. Tularemia
Correct Answer: A

Rationale: The correct answer is A: Anthrax. The clinical presentation of painless necrotic ulcers with black eschar, along with the gram-positive spore-forming bacilli seen on Gram's staining, is classic for cutaneous anthrax. Anthrax is caused by Bacillus anthracis, which produces spores and can lead to skin lesions in individuals working with animals or animal products. Choice B, Chickenpox, typically presents with vesicular rash all over the body. Choice C, Syphilis, is caused by Treponema pallidum and does not present with the characteristic eschar seen in the patient. Choice D, Tularemia, caused by Francisella tularensis, presents with ulceroglandular lesions but lacks the black eschar characteristic of anthrax.

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The degree or extent of disease-evoking power that a microorganism has is referred to as:

  • A. virulence
  • B. strength
  • C. resistance
  • D. competence
Correct Answer: A

Rationale: The correct answer is A: virulence. Virulence refers to the degree or extent of disease-evoking power that a microorganism possesses. This term specifically describes the ability of a microorganism to cause disease in a host. It is a crucial factor in understanding the pathogenicity of different microorganisms.

Choice B: strength is incorrect because it does not specifically relate to the disease-causing potential of a microorganism. Choice C: resistance refers to the ability of an organism to withstand the effects of a particular agent, such as a drug or environmental factor. Choice D: competence is not directly related to the disease-causing ability of a microorganism, but rather refers to the ability of an organism to perform a specific function effectively.

A wound infection culture revealed Gram-positive cocci in clusters. The bacteria were catalase-positive and coagulase-negative. What is the most likely causative agent?

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

Rationale: The most likely causative agent in this case is Staphylococcus epidermidis. This conclusion can be drawn based on the characteristics provided: Gram-positive cocci in clusters, catalase-positive, and coagulase-negative. Staphylococcus epidermidis fits all these criteria.

Explanation of other choices:
- Staphylococcus aureus: Typically coagulase-positive, so it does not match the characteristics given.
- Streptococcus pyogenes: Gram-positive cocci in chains, not clusters. Also, it is catalase-negative.
- Enterococcus faecalis: Gram-positive cocci in pairs or chains, not clusters. Additionally, it is catalase-negative.

Therefore, Staphylococcus epidermidis is the most likely causative agent based on the provided characteristics.

Factors that can increase the chances of vaginitis are:

  • A. urinary blockage, drug use, and stress
  • B. use of antibiotics, pregnancy, and menopause
  • C. puberty, exposure to HPV, and smoking/tobacco use
  • D. menopause, stress, and steroid use
Correct Answer: B

Rationale: The correct answer is B. Vaginitis is often caused by an imbalance in vaginal flora. Antibiotics can disrupt the natural balance, leading to overgrowth of harmful bacteria or yeast. Pregnancy alters hormone levels, making the vagina more susceptible to infection. Menopause decreases estrogen levels, thinning the vaginal walls and reducing beneficial bacteria.

A: Urinary blockage does not directly relate to vaginitis. Drug use and stress may weaken the immune system but are not direct causes of vaginitis.

C: Puberty, HPV exposure, and smoking/tobacco use do not directly increase the chances of vaginitis. HPV is a viral infection, not a direct cause of vaginitis.

D: While menopause can increase the risk of vaginitis due to hormonal changes, stress and steroid use are not primary factors in developing vaginitis.

A patient ill with amebiasis was prescribed a certain drug. The use of alcohol together with this drug is contraindicated because the drug inhibits metabolism of ethyl alcohol. What drug is it?

  • A. Metronidazole
  • B. Reserpine
  • C. Clonidine
  • D. Diazepam
Correct Answer: A

Rationale: Rationale:
1. Metronidazole is known to inhibit aldehyde dehydrogenase, an enzyme involved in alcohol metabolism.
2. Inhibition of this enzyme leads to accumulation of acetaldehyde, causing unpleasant symptoms when alcohol is consumed.
3. This reaction is known as the disulfiram-like reaction.
4. Reserpine, Clonidine, and Diazepam do not have this specific mechanism of action.
Summary:
- Option A (Metronidazole) is correct due to its inhibition of alcohol metabolism.
- Options B, C, and D are incorrect as they do not exhibit this interaction with alcohol metabolism.

Genus Rickettsia representatives are characterized by:

  • A. Gram-positive cell wall
  • B. High resistance to external environment factors
  • C. Intracellular parasitism
  • D. None of the above
Correct Answer: C

Rationale: The correct answer is C: Intracellular parasitism. Genus Rickettsia representatives are known for their ability to live and replicate inside the host's cells, making them obligate intracellular parasites. This characteristic distinguishes them from other bacteria.
A: Gram-positive cell wall is incorrect because Rickettsia have a gram-negative cell wall.
B: High resistance to external environment factors is incorrect because Rickettsia are sensitive to environmental conditions and require specific host cells for survival.
D: None of the above is incorrect because Rickettsia do exhibit the characteristic of intracellular parasitism.

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