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Chapter 9: Pathogenesis of Bacterial Infection

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A 22-year-old woman who works in a plant nursery presents with a history of fever and cough for 2 months. Over this period of time she has lost 5 kg. Chest radiography shows bilateral upper lobe infiltrates with cavities. A stain of her sputum shows acid-fast bacilli. The likely means by which the patient acquired her infection is

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(A) Sexual activity

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(B) Ingesting the microorganisms in her food

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(C) Holding onto contaminated hand rails when she takes public transportation

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(D) Handling potting soil

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(E) Breathing aerosolized droplets containing the microorganism

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During a pandemic of a well-characterized disease, a group of 175 airline passengers flew from Lima, Peru, to Los Angeles. Lunch on the plane included crab salad, which was eaten by about two-thirds of the passengers. After landing in Los Angeles, many of the passengers transferred to other flights with destinations in other parts of California and other Western states. Two of the passengers who stayed in Los Angeles developed severe watery diarrhea. The status of the other passengers was unknown. The likely cause of the diarrhea in the two passengers is

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(A) Escherichia coli O157:H7 (lipopolysaccharide O antigen 157; flagellar antigen 7)

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(B) Vibrio cholerae type O139 (lipopolysaccharide O antigen 139)

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(C) Shigella dysenteriae type 1

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(D) Campylobacter jejuni

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(E) Entamoeba histolytica

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A 65-year-old woman has a long-term central venous catheter for intravenous therapy. She develops fever and subsequently has multiple blood cultures positive for Staphylococcus epidermidis. All of the S epidermidis isolates have the same colony morphology and antimicrobial susceptibility pattern, suggesting that they are the same strain. An S epidermidis biofilm is thought to be present on the catheter. Which one of the following statements about such an infection is correct?

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(A) The biofilm containing the S epidermidis is likely to wash off the catheter.

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(B) Production of an extracellular polysaccharide inhibits growth of the S epidermidis, limiting the infection.

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(C) The S epidermidis in the biofilm are likely to be more susceptible to antimicrobial therapy because the bacteria have decreased rates of metabolism.

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(D) The quorum-sensing ability of S epidermidis results in increased susceptibility to antimicrobial therapy.

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(E) The complex molecular interactions within the biofilm make it difficult to ...

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