DETERMINATION OF THE BACTERIOLOGICAL QUALITY OF RAW-MILK BY AUTOMATICFLUORESCENT MICROSCOPIC COUNTING OF SINGLE BACTERIA (BACTOSCAN-8000) - A REVIEW

The fluorescent automatic microscopic counting of single bacteria in r aw milk (Bactoscan 8000) is applied as a routine method for the determ ination of the bacteriological quality of ex-farm milk in an increasin g number of countries. One major aim of methodological modifications i n the past was to decrease the lower limit of detection due to the inc reasing bacteriological quality of raw milk under the pressure of decr easing class limits by legal requirements. The following descriptive p arameters were derived: lower and upper limit of detection 10-20000 an d >3 mill colony forming units (cfu)/ml, respectively; precision data are dependent on the count level; repeatability r and reproducibility R on a level of 100 Bactoscan Counts (BC) were 0.06 and 0.12 log cfu/m l, respectively; the accuracy of the estimate (s(y,x)) was indicated b y 0.2-0.35 log cfu/ml. Calibration and standardization are, - as for a ll quantitative microbiological methods -, very critical and difficult to solve. Changes in sensitive reagents, as for example, technical st andard and dye, can cause systematic deviations of BCs. The ratio betw een BCs and cfu is influenced by numerous factors, as for example type , number, physiological status of the microorganisms, milk production and time/temperature conditions of the sample. Pure culture trials wit h mastitis pathogens revealed for some types (Staphylococcus aureus, S treptococcus uberis) an underestimation of the cfu using the Bactoscan method.