Enterococci: Part II: Reading Samples


  1. Approximately 24 hours after preparing the samples, remove the trays from the incubator.
  2. Bring the trays and a permanent marker over to the UV light. Fill in the date and time on the right half of each tray.
  3. Turn on the UV light and place one tray under the light. Mark with the marker each well that is illuminated.
  4. Remove the tray from the UV light, count and record the number of illuminated large wells (include the overflow well as a large well), then count and record the number of illuminated small wells.
  5. Using the MPN (Most Probable Number) chart, read and record the MPN for the diluted sample.
  6. Multiply the initial MPN by 10, since the sample is a 1/10 dilution, and record the final MPN. The MPN indicates the number of cfu/100 mL (colony forming units per 100 mL of sample water).
  7. Record the MPN on your group’s data sheets.
  8. Repeat steps 3-7 for each tray, then turn off the UV light and place all trays into the fridge.