Bacteriological diagnosis with Petrifilm of mastitis pathogens in milk samples from each quarter and bulk milk samples

Three experiments were conducted to evaluate four different Petrifllm products (3M, Neuss) for detection of mastitis pathogens in quarter and bulk milk samples, comparing them to the results of standard microbiological techniques. The aim of experiment 1 was to determine the sensitivity of 3M Rapid Coliform Count Plate in identifying clinical mastitis cases caused by coliform bacteria. Within 12 h of incubation, three times more coliform bacteria could be identified with Petrifilm than with the standard technique. For a valid result, milk samples must be free of contamination. Experiment 2 focused on whether Petrifilm was able to monitor S. aureus on bulk milk level in herds being infected with this pathogen. In relation to the gold standard (combination of both procedures (standard and Petrifilm, prevalence 52%), sensitivity for the standard procedure amounted to 15.4% and to 94% for Petrifilm. In Experiment 3 the combination of several Petrifilm (RUEGG, 2004) was compared with the standard diagnostic technique (gold standard). Sensitivity of the Petrifilm method approached the assumed gold standard to 43% and specificity to 29%. The positive predictive value of 28% showed that both procedures are not directly comparable with each other. Due to the definition of a gold standard, the weaknesses of the classical technique can be interpreted as a disadvantage of the Petrifilm procedure. The strength of the available Petrifilm as mastitis diagnostic tools is the identification of S. aureus and coliform microorganisms, moreover E. coli.