HPC for Quanti-Tray Test

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

Quanti-Tray main image


  • Quantifies heterotrophic organisms in a 100 mL format
  • No autoclaving, filtering, or agar
  • No colony counting or interpretation
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  • Convenient 100-mL sample size—test source water, transport vehicle water, manufacturing line water, and finished products.
  • Simple procedure needs no special training.
  • Shares the same Quanti-Tray system as Colilert, Enterolert, and Pseudalert tests for maximum efficiency.
  • Results valid at 44–72 hours.


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 metabolised 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

How to use the HPC for Quanti-Tray test

File Icon  View/Print HPC for Quanti-Tray Test Procedure


Step-by-step guide to using the HPC for Quanti-Tray test


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.


Q & A

Frequently asked questions and answers

Which water types can be tested?
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).

What is the sample incubation time and temperature?
Water samples are incubated at 36ºC (± 2ºC) for 44 hours, and results are valid up to 72 hours.

What is the detection limit?
The HPC for Quanti-Tray test detects heterotrophic organisms at 1 cfu/100 mL.

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

Are results valid prior to 44 hours?
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.

Are results valid after 72 hours?
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.

Can either a 51-well or a 97-well Quanti-Tray be used?
Yes, both the Quanti-Tray and Quanti-Tray/2000 can be used with the HPC for Quanti-Tray test in the 100-mL format.

What are the recommended test storage conditions?
2ºC–25ºC away from light.

What should be the colour and consistency of the test powder?
The HPC for Quanti-Tray test reagent powder should be pink in colour and of a free-flowing, granular consistency. Direct any concerns about the colour or integrity of the powder to IDEXX Technical Service at +44(0)1638 676800 or wateruk@idexx.com. 

How should customers dispose of a positive HPC sample?
Check with your local authority for proper disposal of bacteriological biohazard materials at your facility.

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

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Resources & Product Information


IDEXX Water has reference materials and approval documents to support the many products in our water portfolio.

Product information

HPC for Quanti-Tray Test (20 test pack)
Catalogue number: WHQT-20

HPC for Quanti-Tray Test (200 test pack)
Catalogue number: WHQT-200

HPC for Quanti-Tray /2000 Test (20-test pack combo)
Catalogue number: WHQT2K-20

HPC for Quanti-Tray /2000 Test (200-test pack combo)
Catalogue number: WHQT2K-200

IDEXX Water Customer Support

UK Headquarters

IDEXX Technologies Ltd Units 1B & 1C, Newmarket Business Park, Studlands Park Avenue, Newmarket, Suffolk, CB87ER

Tel: 01638 676800


ISO Certifications

File Icon  ISO 9001:2008

File Icon  ISO 17025:2005

File Icon  ISO 14001:2004