Quantitative and qualitative microbial analysis of raw milk reveals substantial diversity influenced by herd management practices

Abstract

The quantitative (n = 260) and qualitative (n = 24) microbial compositions of raw milk samples were assessed using culture analyses and a molecular inventory based on the rDNA sequences of 1697 isolates. A statistical analysis was also performed to correlate farm practices with the microbial populations present in the milk samples. Ripening bacteria and Pseudomonas were the dominant groups. Milk samples were distinguishable by the different proportions of their microbial groups, which varied among producers. Individual practices influenced the levels of technologically important microorganisms, for example, pre-dipping of teats reduced levels of lactococci. Standard plate counts correlated with the levels of Gram-negative bacteria, Pseudomonas, lactococci and ripening bacteria, depending on the milking season. Lactic acid bacteria and yeasts, which were poorly represented, nevertheless seemed to constitute a resilient basal flora. Qualitative species diversity was considerable, with more than 100 bacterial species identified, dominated by Gram-positive bacteria, notably staphylococci and Corynebacterium.