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J Appl Microbiol. 2007 Apr;102(4):909-15.

Description and validation of a rapid (1 h) flow cytometry test for enumerating thermophilic bacteria in milk powders.

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1
Fonterra Research Centre, Palmerston North, New Zealand. steve.flint@fonterra.com

Abstract

AIMS:

The aim of this study was to develop a rapid assay for enumerating thermophilic bacteria in milk powder.

METHODS AND RESULTS:

The BactiFlow flow cytometer was used to count bacteria based on esterase activity in viable bacterial cells. A protocol for total viable bacteria was modified by heat-treating the sample to selectively label thermophilic bacteria. Samples of milk powder dissolved in 0.1% peptone were treated with 0.8% ethylenediaminetetraacetic acid to reduce background interference because of denatured milk proteins. Either thermophilic bacteria were added to the dissolved milk powder or milk powder solutions were incubated at 55 degrees C for 2-3 h to enrich the natural thermophile population for testing. Results from the BactiFlow were compared with traditional plate count results.

CONCLUSIONS:

Thermophilic bacteria in milk powder can be enumerated within 1 h using the BactiFlow flow cytometer.

SIGNIFICANCE AND IMPACT OF THE STUDY:

Microbiological test results obtained within 1 h can potentially be used to monitor manufacturing processes, effectively trace problems and provide confidence in the manufacture of product.

[Indexed for MEDLINE]
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