A large study by food scientists at the University of California, Davis, found that unpasteurized milk, commonly known as raw milk, contains a large number of antimicrobial resistance genes that can cause dangerous bacteria very quickly when placed at room temperature,media New Atlas reported. The researchers looked at 2,034 milk samples collected from retail stores in five U.S. states (California, Idaho, Arizona, South Carolina and Maine). Four milk processing techniques were studied, from products that were completely unpasteurized to large barrels of pasteurization, short-temperature (HTST) and ultra-pasteurization (UHT) products.
The results showed that the live bacteria content of raw milk samples was significantly higher than that of other processed milks. However, as long as the milk is refrigerated, these bacterial levels do remain stable. The researchers re-positioned the genetic material in the milk sample and found that raw milk “contained significantly more ARGs (antimicrobial resistance genes) than pasteurized milk.” This is the second recent study to detect relevant levels of ARGs in raw milk samples. But more worryingly, when raw milk is placed at room temperature, bacteria with these genes appear very quickly.
“Our study shows that bacteria with antimicrobial-resistant genes can grow, whether intentionally or unintentionally, in raw milk, ” explains co-author Michele Jay-Russell, a microbiologist. “It’s not just about spoiling. If not handled correctly, the risk is really high. “
The researchers expressed particular concern about the production of yogurt. David Mills, co-author of the study, suggests that those keen on making the fermented product should use a start-up culture. This, he says, will help people avoid growing large numbers of antibiotic-resistant bacteria that may be found in raw milk.
“You might just flood your gastrointestinal tract with these genes, ” Mills said. “We no longer live in an antibiotic-free world. These genes are everywhere, and we need to do everything we can to stop them from flowing into our bodies. “
In addition to these significant levels of ARGs in raw milk, the researchers also analyzed the broader bacterial population that existed in the product. Liu Jinxin, lead author of the study, said a large number of “beneficial bacteria” were not found in raw milk samples. The findings run counter to the widely accepted belief that unpasteurized milk contains a large amount of beneficial lactic acid bacteria, which are subsequently destroyed during pasteurization.
“We don’t want to scare people, we want to warn them,” the researchers said. “If you want to continue drinking raw milk, put it in the fridge to minimize its risk of producing bacteria with antibiotic-resistant genes. “
The new study was published in the journal Microbiology.