FRIDAY, July 10, 2020 (HealthDay News) -- If you're a fan of raw milk, keep it chilled. Leaving raw milk at room temperature can release antimicrobial-resistant genes, a new study suggests.
Also, bacteria that have antimicrobial-resistant genes can transfer them to other bacteria, spreading resistance, the researchers said.
"We don't want to scare people, we want to educate them," said researcher Jinxin Liu. "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," added Liu, a postdoctoral researcher in food science and technology at the University of California, Davis.
Some 3% of Americans drink raw milk. That's milk that has not been pasteurized. Many believe raw milk is healthier because it contains probiotics, but the researchers didn't find that.
"Two things surprised us," Liu said in a university news release. "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."
Bacteria with antimicrobial-resistant genes can become "superbugs." Each year, nearly 3 million people get an antibiotic-resistant infection, and more than 35,000 die from one, according to the U.S. Centers for Disease Control and Prevention.
For the study, the team from UC Davis analyzed more than 2,000 milk samples from five states. The investigators found that raw milk had the most antibiotic-resistant microbes when left at room temperature.
Researcher Michele Jay-Russell is a microbiologist and manager with the UC Davis Western Center for Food Safety. She said, "Our study shows that with any temperature abuse in raw milk, whether intentional or not, it can grow these bacteria with antimicrobial-resistance genes. It's not just going to spoil. It's really high risk if not handled correctly."
The report was published online June 26 in the journal Microbiome.
For more on raw milk, visit the U.S. Centers for Disease Control and Prevention.