Characterization and horizontal transfer of qacH-associated class 1 integrons in Escherichia coli isolated from retail meats

- The MICs of 179 E. coli isolates against BC ranged from 4 to 64 μg/mL.
- sugE(c), ydgE/ydgF, mdfA, emrE and qacEΔ1 were commonly present in these isolates.
- Three types of qacH-associated non-classic integrons were observed in four isolates.
- The non-classic integrons were on plasmids of 100-150 kb.
- The 100 kb plasmids were transferrable to another strain of E. coli.

The aim of this study was to examine the presence of genes responsible for resistance to quaternary ammonium compounds (QACs) and the association of qac genes with class 1 integrons in Escherichia coli isolated from retail meats. Among the 179 E. coli isolates tested, the minimum inhibitory concentrations (MICs) of benzalkonium chloride (BC) ranged from 4 to 64 μg/mL. PCR assays indicated that QAC-resistance genes sugE(c), ydgE/ydgF, mdfA, emrE and qacEΔ1 were commonly present (40.2%-88.3%) in these isolates, but qacE, qacF, qacH and sugE(p) were less prevalent (2.2%-28.5%). Seven different gene cassette arrangements were identified in 31 intI1-positive isolates. Three types of qacH-sul3-associated non-classic integrons were observed in four isolates: dfrA12-orfF-aadA2-cmlA1-aadA1-qacH-IS440-sul3, aadA2-cmlA1-aadA1-qacH-IS440-sul3 and dfrA1-aadA1-qacH-IS440-sul3. Non-classic class 1 integrons were located on plasmids of 100-150 kb in these four isolates. Our results demonstrated that the qacH-associated integrons located on 100 kb plasmids in two isolates could be transferred to an E. coli recipient, indicating the co-existence and co-dissemination of disinfectant and antimicrobial resistance genes among bacterial species.