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 ammo-nium 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 retail meats in 2006 were 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 com-mon disinfectants were determined using an agar dilution method. 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 contain more diverse combinations of disinfectant resistance genes than susceptible ones. All isolates showed reduced susceptibility to five of six disinfectants com-pared 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)genes were highly associated with multidrug resistance phenotypes. Using QACs in the food industr