Description and validation of a rapid (1 h) flow cytometry test for enumerating thermophilic bacteria in milk powders.
OBJECTIVE
The aim of this study was to develop a rapid assay for enumerating thermophilic bacteria in milk powder.


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.


CONCLUSIONS
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.
Flint
S
S
Fonterra Research Centre, Palmerston North, New Zealand. steve.flint@fonterra.com
Walker
K
K
Waters
B
B
Crawford
R
R
D000818:Animals; D015169:Colony Count, Microbial; D005434:Flow Cytometry / Q000379:methods*; D005516:Food Microbiology; D001411:Geobacillus stearothermophilus / Q000302:isolation & purification*; D008892:Milk / Q000382:microbiology*; D009520:New Zealand