Semi-automated direct epifluorescent filter technique for total bacterial count in raw milk

The Direct Epifluorescent Filter Technique (DEFT) and the reference method of counting total bacterial colonies on Petri dishes were compared. IDF Sta ndards 128 (1985) and 161A (1995) were applied. A total of 496 samples of m ilk were analyzed. Colony forming units per muL milk were transformed to de cimal logarithmic units: log (cfu/muL). The repeatability standard deviatio n, S-r = 0.114, was typical for a routine microbiological method. To study the carryover at different levels of bacteria, 3 tests were performed on mi lk samples of approximately 100, 700, and >1000 cfu/muL. For the first 2 ex periments, no carryover was detected; in the milk sample with >1000 cfu/muL , the carryover was <0.12%. When the DEFT counts were regressed versus the reference method, the values of the slope and intercept were 0.92 and 0.17, respectively; the correlation coefficient was r = 0.84; and the residual s tandard deviation was S-yx = 0.287. The paired t-test showed that the refer ence method and DEFT do not give significantly different results (p = 0.05) .