Produce may harbor antibiotic resistant genes

A study published in mBio suggests that common supermarket produce may be a reservoir for transferable antibiotic resistance genes that may be missed by traditional detection methods.

“Despite its benefit to human health, consumption of produce is increasingly recognized as a source of pathogenic bacteria, antibiotic-resistant bacteria, and antibiotic resistance genes associated with mobile genetic elements,” wrote the researchers.

The researchers bought mixed salad, arugula, and cilantro—three foods generally consumed raw—from German supermarkets and tested them for resistant bacteria using cultivation- and DNA-based methods. They focused on tetracycline-resistant E. coli because of large amounts of tetracyclines are used in the breeding and care of food animals like pigs and cows and end up making their way into soil through organic fertilizers.

Testing found tetracycline-resistant E. coli isolates on all produce samples. According to the researchers, the profiles of 63 tetracycline-resistant E. coli isolates—mostly from cilantro—showed that almost all were resistant to antibiotics from at least one class and two were resistant to eight classes. Most (84%) were also resistant to ampicillin and amoxicillin, and 73% were resistant to trimethoprim.

DNA extracted from enrichment cultures showed “an impressive diversity of self-transmissible multiple resistance plasmids” in bacteria taken from the produce—results that were missed by direct testing.

“This is the first study demonstrating that multidrug resistance plasmids present in produce-associated bacteria were transferable to sensitive E. coli recipients, a process that could occur in the human gut,” wrote the researchers. “This study highlights the importance of the rare microbiome associated with produce as a source of antibiotic resistance genes that might escape cultivation-independent detection yet may be transferred to human pathogens or commensals.”

Study