©Christine L. Case
Skyline College


Clinical Problem Solving

This problem will provide practice interpreting data and information on an infectious disease. The questions are those that the primary care physician and epidemiologist ask themselves and each other as they solve a clinical problem.


E. coli is a facultatively anaerobic gram-negative rod that produces acid and gas from lactose and does not use citrate as its sole carbon source. E. coli O157:H7 is identified by its somatic (O) and flagellar (H) antigens; it is also sorbitol-negative.

The figure shows DNA fingerprints from E. coli O157:H7 isolates submitted by four different laboratories to PulseNet. The DNA fingerprints were made by Pulsed Field Gel Electrophoresis. The bacteria were isolated from apple juice produced in one state and patients from three different states.

  1. Which isolates are genetically the same? What can you conclude?

  2. Do you need any additional information from the patients?

  3. E. coli is a normal and necessary part of human intestinal microbiota. Why is it necessary to identify E. coli O157:H7?

  4. If these are all E. coli isolates, why do the DNA fingerprints differ?

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