DETERMINATION OF VIABLE BACTERIAL-POPULATIONS IN RAW-MILK WITHIN 20 MINUTES BY USING A DIRECT EPIFLUORESCENT FILTER TECHNIQUE

The results from a shortened procedure for the direct epifluorescent f ilter technique (DEFT) determination of viable bacterial populations i n raw milk were compared to standard plate counts. Shortening the pref iltration trypsin-Triton X-100 incubation period from 10 to 3 min enab led the completion of the analysis within 20 min. The short DEFT metho d results had a correlation coefficient (r) of 0.81 with plate counts. With respect to precision, the average difference between values of d uplicate plate count analyses was 0.16 log units; that of the short DE FT was 0.14 log units. The slopes of the regressions equations were le ss than 1, indicating that a direct correlation is not achieved. Short DEFT values were 0.17 log units higher than those of plate counts on milk samples containing less than 10,000 CFU/ml. For milk samples cont aining counts over 10,000 CFU/ml, short DEFT values averaged only 0.05 log units above plate count readings. Daily preparation of the stain appears unnecessary since acridine orange solutions stored for up to 2 days at 4 degrees C did not produce results significantly (P > 0.05) different from those obtained with fresh solutions. The short DEFT met hod has potential for the assessment of the bacteriological quality of raw milk in tanker deliveries.