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Supermarket produce contains transferable antibiotic-resistant genes
Common supermarket produce is a reservoir for transferable antibiotic resistance genes that may be missed by traditional detection methods, researchers found.
“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,” Khald Blau, a PhD student and guest researchers at the Julius Kühn Institut Federal Research Center for Cultivated Plants in Germany, and colleagues wrote.
“Recently, several foodborne disease outbreaks have been associated with produce contamination worldwide,” they continued. “The microbiome of produce is important for plant health and vigor and was shown to be highly dynamic during growth and postharvest, but can also contain pathogenic bacteria from human and animal sources, including Escherichia coli strains.”
Blau and colleagues 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, according to the study. They focused on tetracycline-resistant E. coli because of the large amounts of tetracyclines used in the breeding and care of food animals like pigs and cows which make their way into soil through organic fertilizers.
Testing found tetracycline-resistant E. coli isolates on all produce samples. According to Blau and colleagues, 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,” Blau and colleagues wrote.
“Produce is one of the most popular food commodities. Unfortunately, leafy greens can be a reservoir of transferable antibiotic resistance genes. 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.” – by Caitlyn Stulpin
Disclosures: The authors report no relevant financial disclosures.