Drug-Resistant Bugs Found in Organic Meat
If you’re paying premium prices for pesticide- and antibiotic-free meat, you might expect that it’s also free of antibiotic-resistant bacteria. Not so, according to a new study. The prevalence of one of the world’s most dangerous drug-resistant microbe strains is similar in retail pork products labeled “raised without antibiotics” and in meat from conventionally raised pigs, researchers have found.
Methicillin-resistant Staphylococcus aureus (MRSA), a drug-resistant form of the normally harmless S. aureus bacterium, kills 18,000 people in the United States every year and sickens 76,000 more. The majority of cases are linked to a hospital stay, where the combination of other sick people and surgical procedures puts patients at risk. But transmission also can happen in schools, jails, and locker rooms (and an estimated 1.5% of Americans carry MRSA in their noses). All of this has led to a growing concern about antibiotic use in agriculture, which may be creating a reservoir of drug-resistant organisms in billions of food animals around the world.
Tara Smith, an epidemiologist at the University of Iowa College of Public Health in Iowa City who studies the movement of staph bacteria between animals and people, wondered whether meat products might be another mode of transmission. For the new study, published this month in PLoS ONE, she and colleagues bought a variety of pork products—395 packages in all—from 36 different stores in two big pig farming states, Iowa and Minnesota, and one of the most densely populated, New Jersey.
In the laboratory, the team mixed meat samples “vigorously” with a bacterial growth medium and allowed any microbes present to grow. MRSA, which appears as mauve-colored colonies on agar plates, was genetically typed and tested for antibiotic susceptibility.
The researchers found that 64.8% of the samples were positive for staph bacteria and 6.6% were positive for MRSA. Rates of contamination were similar for conventionally raised pigs (19 of 300 samples) and those labeled antibiotic-free (seven of 95 samples). Results of genetic typing identified several well-known strains, including the so-called livestock-associated MRSA (ST398) as well as common human strains; all were found in conventional and antibiotic-free meat.