Rapid enumeration of bacteria grown on surimi-based products by flow cytometry

A rapid method to enumerate bacteria adhered on a surimi-based product (kam aboko) by flow cytometry (FCM) is described. To remove Escherichia coli cel ls from the surface of kamaboko, ultrasonic energy was used. Almost all cel ls can be removed from kamaboko in 3 min with ultrasonic treatment. Because the sample might contain various non-bacterial particles such as food addi tives and debris of products, propidium iodide was used to discriminate bac terial cells from nonbacterial particles. Fluorescence scattergrams could d istinguish bacteria from the particles, and the FCM method could be used to enumerate bacteria adhered on the surface of kamaboko during storage. Cell numbers determined by FCM paralleled well with those measured using a trad itional colony counting method in the range of 10(4)-10(1) cells/g. The FCM assay could enumerate cells within 1 min and the total assay time, includi ng sample preparation, was less than 30 min.