Presence of Heavy Metal Resistance Genes in Escherichia coli and Salmonella, and Analysis of Resistance Gene Structure in E. coli E308.

Little attention has been paid to heavy metal resistance (HMR) to pathogenic bacteria with the wide use of heavy metals as feed additives in food animals. Therefore, present study was constructed to investigate the presence of HMR in Escherichia coli and Salmonella, and its correlation with disinfectant resistance genes (DRGs) and antibiotic resistance genes (ARGs).The heavy metal resistance genes (HMRGs) of 178 E. coli and 294 Salmonella isolated from chicken farms and retail meats were detected by polymerase chain reaction (PCR). The minimal inhibitory concentrations (MICs) of heavy metals were determined by broth micro-dilution method. The complete-genome of E. coli E308 which had indications of multi-resistance was recovered and assembled using third-generation sequencing.Results showed that frequency of different HMRGs in E. coli and Salmonella ranged 0.60 - 77.0% and 0.30 - 87.1%, respectively. MICs of heavy metals for E. coli and Salmonella ranged widely from ≤ 12.5 mg/L to 1600 mg/L. Moreover, the HMRGs (zntA, arsB, merA, pcoR, pcoA, pcoC and chrA) were found to be significantly associated with one or more DRGs (sugE(c), emrE, mdfA, ydgE/ydgF, qacF, sugE(p) and qacEΔ1) and ARGs (sul1, sul2, sul3, tetA, tetB, tetC, bla, bla and bla) (p < 0.05).The present study demonstrated that HMRGs were widely present in E. coli and Salmonella isolated from chicken farm and retail meats, and the association between HMRGs with DRGs and ARGs may lead to the co-resistance of heavy metals and other antimicrobials.