A flow cytometry method for rapid detection and enumeration of total bacteria in milk

Application of flow cytometry (FCM) to microbial analysis of milk is hampered by the presence of milk proteins and lipid particles. Here we report on the development of a rapid (less than or equal to 1-h) FCM assay based on enzymatic clearing of milk to determine total bacteria in milli. When bacteria were added to ultra-heat-treated milk, a good correlation (r greater than or equal to 0.98) between the FCM assay and the more conventional methods of plating and direct microscopic counting was achieved. Raw milk data showed a significant correlation (P < 0.01) and a good agreement (r = 0.91) between FCM and standard plate count methods. The detection limit of the FCM assay was less than or equal to 10(4) bacteria mi of milk(-1). This limit is below the level of detection required to satisfy legislation in many countries and states.