Characterization of bacterial population of raw milk from bovine mastitis by culture-independent PCR–DGGE method

Culture-independent PCR–DGGE fingerprinting was used to reveal the bacterial composition and diversity associated with raw milk of mastitis-infected cows from Hokkaido, Japan for the first time. All the mastitic milk samples were diagnosed as solely infected by coliforms using the classical microbiological method following on-farm culturing. The variation in community structure between each sample observed in our results indicated that the bovine mastitis-associated bacteria were host-specific. Klebsiella pseudomoniae, Lactococcus lactis, Staphylococcus aureus and members of the Escherichia genus were found to be widely distributed. Furthermore, more than one pathogen known to cause mastitis was found to be present in some milk samples. These pathogens are not only potential etiological agents but may also play a role in disrupting the natural microbial ecology in mastitic cows. This finding highlights the limitation of the traditional identification and characterization strategy, and the PCR–DGGE are shown to be a powerful tool for describing the bacterial flora and especially etiological agents in mastitic milk.