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

J Appl Microbiol. 2007 Apr;102(4):909-15. doi: 10.1111/j.1365-2672.2006.03167.x.


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.

MeSH terms

  • Animals
  • Colony Count, Microbial
  • Flow Cytometry / methods*
  • Food Microbiology*
  • Geobacillus stearothermophilus / isolation & purification*
  • Milk / microbiology*
  • New Zealand