HPC for Quanti-Tray*

Heterotrophic plate count made easy for bottling and manufacturing plants and on-premise testing


  • Quantifies heterotrophic organisms in a 100 mL format
  • No autoclaving, filtering, or agar
  • No colony counting or interpretation

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How the HPC for Quanti-Tray test works

The HPC for Quanti-Tray test is used for the quantification of heterotrophic organisms in 100 mL of water.

The test is based on the IDEXX proprietary Multiple Enzyme Technology, which detects viable heterotrophic organisms by testing for the presence of key enzymes known to be present in these organisms. The test uses multiple enzyme substrates that produce blue fluorescence when metabolized by waterborne bacteria.

The sample/reagent mixture is added to a Quanti-Tray, incubated, and then examined for fluorescing wells. The number of fluorescing wells corresponds to a most probable number (MPN) of total heterotrophic organisms in the original sample.

The HPC for Quanti-Tray test detects organisms at 1 cfu/100 mL after 44–72 hours of incubation.




How to use



Step 1

Add reagent to sample (sample will turn pink).

Step 2

Pour into Quanti-Tray or Quanti-Tray/2000.

Step 3

Seal using a Quanti-Tray Sealer; incubate for 44 hours.

Step 4

Read under ultraviolet light; count blue fluorescent wells and refer to MPN table.

Frequently asked questions


The HPC for Quanti-Tray test is designed specifically for bottled-water samples. Bottled-water samples are defined as samples taken from any point in the bottled-water manufacturing process (from the original water source, to transportation vehicles, to the manufacturing line, to the finished product).

Water samples are incubated at 36ºC (± 2ºC) for 44 hours, and results are valid up to 72 hours.

The HPC for Quanti-Tray test detects heterotrophic organisms at 1 cfu/100 mL.

There is no comparator for the HPC for Quanti-Tray test. Use a negative control for comparison when you interpret results.

Yes, if the results are positive. An inoculated HPC for Quanti-Tray test sample that is positive before 44 hours is a confirmed positive test. However, for an accurate quantitative determination of heterotrophic count in a sample, the results should be read between 44 and 72 hours of incubation.

Yes, if the results are negative. If an inoculated HPC for Quanti-Tray test sample is inadvertently incubated over 72 hours, lack of fluorescence is a valid negative test. However, a fluorescent read after the 72 hours is not valid and should be repeated or verified.

Yes, both the Quanti-Tray and Quanti-Tray/2000 can be used with the HPC for Quanti-Tray test in the 100-mL format.

The HPC for Quanti-Tray test reagent powder should be pink in color and of a free-flowing, granular consistency. Direct any concerns about the color or integrity of the powder to IDEXX Technical Service at 1-800-321-0207 or

Check with your local, state, and/or federal authorities for proper disposal of bacteriological biohazard materials at your facility.

The HPC for Quanti-Tray test should not be used with carbonated water samples.

Resources & Tools

Tests & Accessories

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Product Information

HPC for Quanti-Tray Test (20 test pack)
Product number: 98-2389-00
Catalog number: WHQT-20
HPC for Quanti-Tray Test (200 test pack)
Product number: 98-27390-00
Catalog number: WHQT-200
HPC for Quanti-Tray /2000 Test (20-test pack combo)
Product number: 99-27855
Catalog number: WHQT2K-20
HPC for Quanti-Tray /2000 Test (200-test pack combo)
Product number: 99-27856
Catalog number: WHQT2K-200


IDEXX Water has reference materials and approval documents to support the many products in our water portfolio. Find the document(s) you need by selecting the link below.

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Water Customer Support

Corporate Headquarters
IDEXX Laboratories, Inc.
One IDEXX Drive
Westbrook, Maine 04092 USA

Tel: 1-800-321-0207
Fax: 1-207-556-4630

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*The HPC for Quanti-Tray Test is intended to be used only for water quality research and analysis, by technically qualified individuals or under their supervision.