Fitness Of Bacteria Carrying Aac?6'?-Ib-cr Or Aac?6'?-Ib-cr+bla_CTX-M-27gene

Plasmid-mediated quinolone resistance?PMQR?determinants have attracted much attentionworldwide since theywere discovered,particularthe aac?6'?-Ib-cr gene,which conferring resistance to both fluoroquinolones and aminoglycosides having being often found in CTX-M type ESBLs-producing enterobacterial isolates,showing higher-level resistance to both the third generation cephalosporins and fluoroquinolones.Our previous study demonstrated that bacteria carrying aac?6'?-Ib-cr plasmid might contribute the capture of the other resistant plasmid.In present study,weintended to construct both E.coliJ53andS.entericaSH10strainscarryingaac?6'?-Ib-cr,bla_{CT X-M-27}and aac?6'?-Ib-cr+bla_{CT X-M-27}plasmid,respectively,exploringthe effect of strains carrying single or double resistance plasmids on drug resistance,bacteria fitnessas well asthe abilities of biofilm formation.The outcomings of the present study provided foundation to understand the effect of aac?6'?-Ib-cr gene on the development of drug resistance,bacteria fitness and the development of high level resistance when co-exist with CTX-M type ESBLs gene.BothE.coliJ53 and S.enterica SH10strainscarryingaac?6'?-Ib-cr,bla_{CT X-M-27} and aac?6'?-Ib-cr+bla_{CT X-M-27}plasmid,respectively,wereconstructedviatransformation experiments.ThetransformantswereassignedasJ53+aac?6'?-Ib-cr,J53+bla_CTX-M-27,J53+aac?6'?-Ib-cr+bla_{CT X-M-27},SH10+bla_CTX-M-27,SH10+aac?6'?-Ib-cr+bla_{CT X-M-27},and SH10+aac?6'?-Ib-cr,respectively.Susceptibilities of the strains to several kinds of antimicrobial agents were determined by the double agar dilution method.The results showed that compared with the parental strain J53 and SH10,the MICs of ciprofloxacin and kanamycin for the strains carringaac?6'?-Ib-crplasmid increased 2-4 folds and 32-128 folds,respectively.The strains carrying bla_CTX-M-27 plasmid showed enhanced resistance to cephalosporins,particular tocefotaximeandceftiofurinSH10transformant.TheJ53carrying aac?6'?-Ib-cr+bla_{CT X-M-27}double plasmidsdemonstranted further elevated MICs for cephalorporins and quinolones comparing with SH10 double plasmid transformant.Thefitnessofthestrainscarryingaac?6'?-Ib-cr,bla_CTX-M-27and aac?6'?-Ib-cr+bla_{CT X-M-27}weredetermined via performing the growth ability,the plasmid stability,andgrowth competition experiments.Results derived from plasmid stability experiment showedthat when the strains were passaged on the eighth day,the proportion of the strains carrying bla _CTX-M-27 plasmid was 100%,carryingaac?6'?-Ib-crfalling to 80%,carryingaac?6'?-Ib-cr+bla _CTX-M-27fallingto85%.StrainJ53carrying bla_{CT X-M-27},aac?6'?-Ib-cr+bla_{CT X-M-27} had a similar growth abilities as the parental strains,but all better than that carrying aac?6'?-Ib-cr.While strain SH10 carrying aac?6'?-Ib-cror bla_{CT X-M-27} showed a similar growth abilities as the parental strains,but all better than that carrying aac?6'?-Ib-cr+bla _CTX-M-27.The results from competition experimentsshowed that strainscarryingdoubleplasmids(J53+aac?6'?-Ib-cr+bla_{CT X-M-27}and SH10+aac?6'?-Ib-cr+bla_{CT X-M-27})were more competitive than that carrying single aac?6'?-Ib-cr plasmid?J53+aac?6'?-Ib-crand SH10+aac?6'?-Ib-cr?,while had an obvious competitive disadvantage than that carrying single bla_CTX-M-27 plasmid(J53+bla_CTX-M-27 and SH10+bla_CTX-M-27).Strains carrying single bla _CTX-M-27plasmids(J53+bla_CTX-M-27 and SH10+bla_CTX-M-27)were significantly more competitive than parental strains and that carrying single aac?6'?-Ib-crplasmids?J53+aac?6'?-Ib-cr and SH10+aac?6'?-Ib-cr?.The above results suggested that aac?6'?-Ib-cr alone in plasmid was unable persisting,while coexistingwith bla_CTX-M-27could improve the fitnessin favor of spread of resistance genes communication.However bla _CTX-M-27 alone in plasmid could be stable and persisting in bacteria.Strains J53 and SH10 had no orweakability to form biofilm.O nce carrying single plasmid(bla_CTX-M-27or aac?6'?-Ib-cr),the strains had theability to form biofilm.Furthermore,strains carrying double plasmids(aac?6'?-Ib-cr and bla_{CT X-M-27})showed stronger abilities of biofilm formation.Conclusion:aac?6'?-Ib-cralone in plasmid was not stable,however coexistence with bla_{CT X-M-27}could improve the fitness and competiton,and enhancing the abilities to form biofilm,leading the spread of resistance genes.