It’s been a time of slow news on the raw milk front the last few years. The big reason is that producers of unpasteurized dairy appear to have gotten their collective arms around contamination challenges, generating much less news about outbreaks of illness from pathogens like E.coli O157:H7 and campylobacter. That has meant less opportunity for the nay-sayers to do their fear-mongering than was once the case.
But that doesn’t mean the fear-mongering has ended. A new study raises a specter of danger for raw milk drinkers: antibiotic-resistant bacteria rather than beneficial lactic acid bacteria are shown to dominate the microflora of raw milk left to ferment, or clabber, at room temperature.
A team of five scientists from the University of California in Davis has spent the last three years sampling and measuring more than 2,000 retail milk samples—raw and pasteurized— collected from stores in California, Idaho, Arizona, South Carolina, and Maine.
In a paper published in the journal Microbiome, the researchers stated that “the results presented here suggest that spontaneous fermentation does not grow beneficial lactic acid bacteria and instead, enrichment of ARGs (antibiotic resistance genes) occurred even within a short period of RT (room temperature) incubation. In addition to ARGs enriched due to intentional RT fermentation, proper cold-chain maintenance can fail during transportation from the raw milk producer to the consumer or in the home of the consumer, and therefore inadvertent short-term RT incubations can also happen. Such incubation likely enriches populations of bacteria in milk which in turn contributes to a modified resistome with elevated prevalence of ARGs.”
At this point, you may be wondering: what are the dangers of adding antibiotic resistant bacteria to my gut flora? While it certainly doesn’t sound like a great thing to be ingesting, the short answer is no one knows for sure. Heck, researchers don’t even know where the antibiotic-resistant bacteria come from, especially since much of the raw milk is produced by dairies that are ostensibly organic, and claim their cows are grass fed. As the U CA researchers put it in their paper: “A better understanding of the diversity of ARG content as well as the biogeography, health risk associations and methods to reduce this ARG reservoir, is clearly warranted.”
The research team actually concluded that raw milk kept refrigerated during its journey through the supply chain does okay. Compared with pasteurized milk, “Raw milk samples had the highest prevalence of viable bacteria which were measured as all aerobic bacteria, coliform, and Escherichia coli counts, and their microbiota was distinct from other types of milk.”
In a blog post at the U CA, Davis, the lead author, Jinxin Liu, states, “We don’t want to scare people, we want to educate them. If you want to keep drinking raw milk, keep it in your refrigerator to minimize the risk of it developing bacteria with antibiotic-resistant genes.” The researcher adds: “Two things surprised us,. We didn’t find large quantities of beneficial bacteria in the raw milk samples, and if you leave raw milk at room temperature, it creates dramatically more antimicrobial-resistant genes than pasteurized milk.”
The blog post begins to fear monger when it states, “Bacteria with antimicrobial-resistant genes, if passed to a pathogen, have the potential to become ‘superbugs,’ so that pharmaceuticals to treat infection or disease no longer work. Each year, almost 3 million people get an antibiotic-resistant infection, and more than 35,000 people die, according to the Centers for Disease Control.”
The study leaves any number of questions unanswered, including: What is the microflora situation with raw milk sold directly to consumers from farms via herdshare and individual sales? Where does the antibiotic resistance come from in organic raw milk? Why do the beneficial bacteria get overwhelmed by the antibiotic resistant bacteria? And how is production of kefir, based on addition of starter bacteria, affected by such milk? Clearly there is more research to be done here. In the meantime, raw milk drinkers buying their milk at retail outlets might want to think twice before they clabber their milk.