The microbial content of raw and pasteurized cow milk as determined by molecular approaches

J Dairy Sci. 2013 Aug;96(8):4928-37. doi: 10.3168/jds.2013-6688. Epub 2013 Jun 5.


The microbial composition of raw and pasteurized milk is assessed on a daily basis. However, many such tests are culture-dependent, and, thus, bacteria that are present at subdominant levels, or that cannot be easily grown in the laboratory, may be overlooked. To address this potential bias, we have used several culture-independent techniques, including flow cytometry, real-time quantitative PCR, and high-throughput DNA sequencing, to assess the microbial population of milk from a selection of commercial milk producers, pre- and postpasteurization. The combination of techniques employed reveals the presence of a previously unrecognized and diverse bacterial population in unpasteurized cow milk. Most notably, the use of high-throughput DNA sequencing resulted in several bacterial genera being identified in milk samples for the first time. These included Bacteroides, Faecalibacterium, Prevotella, and Catenibacterium. Our culture-independent analyses also indicate that the bacterial population of pasteurized milk is more diverse than previously appreciated, and that nonthermoduric bacteria within these populations are likely to be in a damaged, nonculturable form. It is thus apparent that the application of state-of-the-art approaches can provide a detailed insight into the bacterial composition of milk and could potentially be employed in the future to investigate the factors that influence the composition of these populations.

Keywords: flow cytometry; high-throughput DNA sequencing; quantitative PCR.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cattle
  • Flow Cytometry / methods
  • High-Throughput Nucleotide Sequencing / methods
  • Milk / chemistry
  • Milk / microbiology*
  • Pasteurization / standards*
  • Real-Time Polymerase Chain Reaction / methods