Standard bacterial testing for organic raw milk is 'not sufficient', study finds

Laboratory pasteurization count (LPC) is used to assess raw milk quality; this data is used by some dairy producers to designate raw milk quality premiums paid to farmers and may also be used for troubleshooting bacterial contamination issues.

LPC typically enumerates thermoduric bacteria – the type that can withstand pasteurization – but it’s not known the type of bacteria, e.g. sporeformers or non-sporeformers, can be determined by just by looking at the LPC level.

To test if LPC levels can be an indicator of the type of bacteria present in raw milk, researchers from Cornell University collected 94 organic raw milk samples from across the US, assessed these via LPC, and characterized the bacterial isolates.

They found LPC concentrations that ranged from undetectable to 4.07 log10 cfu/mL, and 380 bacterial isolates were analyzed, with the thermoduric bacteria isolated from the samples being split in 3 groups: gram-positive sporeformers (52%), gram-positive non-sporeformers (44%) and gram-negative bacteria (2.4%).

In terms of the LPC levels, the majority of samples (66) had a LPC ≤100 cfu/mL; 6 samples were with a LPC between 100 and 200 cfu/mL, and 10 samples – with a LPC ≥200 cfu/mL. Additional analysis showed that there was an inverse trend between the proportion of gram-positive sporeformers and the LPC concentration – samples with higher LPC had lower proportions of gram-positive sporeformers. But that trend was not significant, according to the research team.

“LPC level alone provides no insight into the makeup of the thermoduric population in raw milk and further characterization is needed to elucidate the bacterial drivers of elevated LPC in raw milk,” the researchers concluded.