Presence of disinfectant resistance genes in Escherichia coli isolated from retail meats in the USA

Objectives: To examine the distribution of all genes known to be responsible for resistance to quaternary ammonium compounds (QACs), and their association with resistance to QACs and other antimicrobials, in Escherichia coli recovered from retail meats. Methods: A total of 570 strains of E. coli isolated from US retailmeats in 2006were screened for the presence of 10 QAC resistance genes [qacE, qacED1, qacF, qacG, emrE, sugE(c), sugE(p), mdfA and ydgE/ydgF]. The MICs of six common disinfectants were determined using an agar dilutionmethod. Possible associations between the presence of the gene and bacterial resistance to QACs and antimicrobials were investigated. Results: emrE, sugE(c), mdfA and ydgE/ydgF were commonly present (77.2%- 100%) in the E. coli isolates, but qac and sugE(p) were less prevalent (0.4%- 22.3%). emrE- mdfA- sugE(c)- ydgE/F was the most common QAC resistance gene profile. A significant association was found between antimicrobial resistance and the presence of sugE(p) and qacED1 (P < 0.05). Antimicrobial- resistant E. coli isolates tended to containmore diverse combinations of disinfectant resistance genes than susceptible ones. All isolates showed reduced susceptibility to five of six disinfectants compared with the control strains. Higher MICs were generally associated with the presence of qac and sugE(p) genes. Conclusions: The QAC resistance genes were commonly present among E. coli isolated from retail meats, and the qac and sugE(p) geneswere highly associatedwithmultidrug resistance phenotypes. UsingQACs in the food industry may not be as effective as expected and could provide selection pressure for strains with acquired resistance to other antimicrobials.