Coexistance of two transferable plasmids-encoding ampC and/or ESBLs in one E.coli cell

Objective:To determine the genetic forms of plasmids-encoding ampC and/or extended spectrum β lactamases(ESBLs) in isolates of E.coli. Methods:Forty-two isolates of E.coli classified as AmpC β-lactamase producers according to the three-dimensional test were collected. The transferability of the third generation cephalosporins resistances was tested in broth mating experiments using an E.coli C600 recipient and CRO and CAZ/CTX/CA for selection of transconjugants.Donors and transconjugants were compared with PCR amplification of plasmid-encoded ampC and(ESBLs) genes, three-dimensional extract patterns and antimicrobial susceptibility testing.Results:These experiments showed that the resistant determinants for the third generation cephalosporins were transferable from 37 donors at the frequency of approximately 10~(-7)to 10~(-5) transconjugants/recipient,while ESBLs determinants alone were transferable from 23 donors,AmpC determinants alone were from 3 donors,both AmpC and ESBLs determinants were from 11 donors.Among these 11 strains,AmpC/ESBLs determinants carried on one plasmid were from 7 donors,transconjugants derived from the other 4 donors each showed 2 types,2 donors each derived both(ESBLs-producing) transconjugant and AmpC/ESBLs-producing transconjugant and the other 2 donors each derived both ESBLs-producing transconjugant and AmpC-producing transconjugant.Conclusion:The coexisting ESBLs-and ampC-enzymes in some E.coli could not be separated by conjugation experiments,while some could be separated when two transferable ampC-and/or ESBLs-encoding plasmids coexisted in one cell.