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Testing Microbiology Samples


We follow these rules specifically. The process is very easy, but make sure you follow the rules and you'll be performing from memory before you know it!!!

Hands must be washed before putting on gloves.
Surfaces must be wiped down with sodium hypochlorite (bleach water) before and after testing.


  • Label tray with site number, collection time/date, processing time/date, processor's initials.
  • Retrieve sample and Colilert from refrigerator.
  • Aseptically (just means free of pathogenic microorganisms) add one packet of reagent to the sample.
  • Re-cap bottle and shake until reagent is mostly dissolved. (If sample "flashes blue" it contains excessive chlorine and is invalid for analysis)
  • Pour into Quanti-Tray.
  • Place tray in rubber insert for Quanti-Tray sealer machine. The sealer works like a laminator and seals the backing onto the tray.

  • Feed tray into Quanti-Tray sealer.


  • Place tray into incubator and incubate at 35.0 degrees Celsius for 24 hours. 


After incubation, the tray is removed from incubator and results are read.

Charts used for reading results

  • Tray is placed under UV light and fluorescence. Tray wells that fluoresce are positive for E. coli, and this number is proportional to the number of E. coli present in the sample. Compare counted number to the designated chart and record results in the MICROBIOLOGY LAB NOTEBOOK.

  • The wells that turn yellow while in incubation proved total coliform bacteria are present. Observe number of yellow samples within the wells and compare to the designated chart and record results in the MICROBIOLOGY LAB NOTEBOOK.


Turn off IDEX machine and UV light. All areas must be wiped down with sodium hypochlorite when testing is complete. Samples should be thrown away in the RED BIOHAZARD bag upon recording in the lab notebook.

**ALL RESULTS ARE REPORTED AS MPN/100ml**
MPN (Most Probable Number)

Templates in the lab notebook make it VERY easy to record results!



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