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Validation of Petrifilm plates for enumeration of total bacteria, psychotropic bacteria, and coliforms in goat milk

S. S. Chen, J. S. Van Kesse, B. Bah, F. Z. Ren, and S. S. Zeng

Journal of Animal Science 85(Supplement 1):487. 2007

PetrifilmTM Aerobic Count (AC) and Coliform Count (CC) plates were validated against standard methods for enumeration of coliforms, total bacteria, and psychrotrophic bacteria in raw (n = 39) and pasteurized goat milk (n = 17) samples. All microbiological data were transformed into log form and statistically analyzed using paired comparison t-test of SAS. There were no significant differences (P < 0.01) between PetrifilmTM CC and the standard Violet Red Bile Agar Petri dish method. PetrifilmTM AC was as accurate (P > 0.05) as the standard Petri dish methods for both total bacteria and psychrotrophic bacteria when the total bacteria count was less than 1x106 CFU/ml. Correlations between PetrifilmTM plates and the standard Petri dish agar methods were high (r = 0.992, 0.997, and 0.974 for coliform, total bacteria, and psychrotrophic bacteria, respectively). In conclusion, PetrifilmTM AC and CC plates can be used as alternatives to standard methods for enumeration of total bacteria, psychrotrophic bacteria, and of coliforms, respectively. Advantages of PetrifilmTM plates include rapidity, ease of performance, labor saving, and no need for agar preparation or autoclaving. This validation is of practical importance to goat milk producers and processors because of the limited numbers of goat milk samples available daily and the lack of advanced laboratory facilities on most goat farms and in most goat milk processing plants.


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