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Chapter 47: Principles of Diagnostic Medical Microbiology

A 47-year-old woman had a bone marrow transplant as part of her treatment for chronic myelogenous leukemia. While in the hospital she had a central venous catheter in place for administration of fluids. In the time following the transplant, but before it had engrafted, the patient had a very low white blood cell count. She developed a fever, and blood cultures were done. Which of the following scenarios suggests that the positive blood cultures resulted from a contaminant?

(A) Two positive peripheral vein blood cultures with Staphylococcus aureus

(B) Two positive peripheral vein blood cultures with Staphylococcus epidermidis along with two positive central line blood cultures with Staphylococcus epidermidis

(C) One positive peripheral vein blood culture and one positive central line blood culture with Escherichia coli

(D) One positive central venous line blood culture with a Corynebacterium species and two negative peripheral vein blood cultures

(E) Two positive central line blood cultures with Candida albicans

Two days ago, a 22-year-old man returned from a 2-week trip to Mexico. Within 24 hours, he developed diarrhea. Which of the following will not establish the etiology of his diarrhea?

(A) Stool culture for Salmonella, Shigella, and Campylobacter

(B) Stool culture for rotavirus and Norwalk-like virus

(C) Stool enzyme immunoassay for Giardia lamblia antigen

(D) Stool examination for Entamoeba histolytica

A 37-year-old man traveled to Peru during the time of the cholera epidemic. One day after returning home, he developed severe watery diarrhea. To enhance the isolation of Vibrio cholerae from his stool, the laboratory needs to include:

(A) MacConkey agar

(B) Campylobacter blood agar

(C) Thiosulfate citrate bile salts sucrose agar

(D) Bismuth sulfite agar

(E) Hektoen agar

A 42-year-old man is known to have HIV/AIDS. Which of the following is the most appropriate method to follow the progress of his highly active antiretroviral therapy (HAART)?

(A) Determination of viral load

(B) Following anti-HIV-1 antibody levels

(C) Using Western blot to assess his anti-p24 levels

(D) Repeated culture of his blood for HIV-1 to ...

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