In a new study, researchers found that raw or unpasteurized cows’ milk from U.S. retail stores can hold a huge amount of antimicrobial-resistant genes if left at room temperature.
They also found bacteria that harbored antimicrobial-resistant genes can transfer them to other bacteria, potentially spreading resistance if consumed.
The research was conducted by a team at the University of California, Davis.
An estimated 3 percent of the U.S. population consumes unpasteurized, or raw, milk, which has not been heated to kill pathogens and extend shelf life.
Raw milk is often touted to consumers as having an abundant supply of probiotics, or healthy bacteria, compared with pasteurized milk. The researchers did not find that to be the case.
In the study, the team analyzed more than 2,000 retail milk samples from five states, including raw milk and milk pasteurized in different ways.
They found raw milk had the highest prevalence of antibiotic-resistant microbes when left at room temperature.
If people leave raw milk at room temperature, it creates dramatically more antimicrobial-resistant genes than pasteurized milk.
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.
Some consumers are intentionally letting raw milk sit outside of the refrigerator at room temperature to ferment, in order to make what’s known as clabber.
The team said if consumers eat raw milk clabber, they are likely adding a high number of antimicrobial-resistant genes to their gut.
The team says if people want to keep drinking raw milk, keep it in the refrigerator to minimize the risk of it developing bacteria with antibiotic-resistant genes.
One author of the study is Jinxin Liu, a postdoctoral researcher in the Department of Food Science and Technology at UC Davis.
The study is published in the journal Microbiome.
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