Study On Drug Resistance And Related Genes In Escherichia Coli Isolated From Chickens In Hefei Area

Modern poultry industry increasingly become large-scale and intensive,which caused colibacillosis has become one of the major infectiousdiseases and has brought great economic loss to poultry industry.To control and treat colibacillosis,abuse and overuse of antibiotics has brought severe resistance,multi-drug-resistance isolates(MDR)and a serious threat to human health and the development of poultry industry.The aim of this study is to investigate the prevalence and propagating characteristics of class 1 integrons,extended-spectrum ?-lactamase(ESBL)genes,plasmid-mediated fluoroquinolone resistance(PMQR)genes,tetracycline-resistant genes,phenicol-resistant genes and 16 S rRNA methylase genesand their coexistence in 184 Escherichia coli(E.coli)isolates collected from chicken farms in Hefei area Anhui province.The minimum inhibitory concentrations(MICs)of 15 antimicrobials were determined using the broth micro-dilution method,according to the guidelines issued by the Clinical and Laboratory Standards Institute(CLSI,2010).The results showed that there were significant difference between resistance rates to different antibiotics in 184 E.coli isolates.High rates of resistance to OTC(97.8%),SUL(97.3%),DC(90.2%),AMX(82.6%),LOM(77.7%),OFX(67.4%),ERO(55.9%)and FFC(52.7%)and low rates of resistance to AMI(7.6%)and SAR(2.2%)were observed.72.3% of the isolates were resistant to at least six antimicrobial agents,while 13.6% were resistant to at least 10 of these drugs,which indicated that the phenomenon of multiple antibiotic-resistance was quite serious.Based on acquirement of the antimicrobial resistance patterns,integrase genes and gene cassettes was amplified by PCR using specific primers,then the gene cassettes were examined by sequencing analysis.The results showed that 91(49.5%)strains harbored classIintegrons,no class II integron was detected.Seventy of the 91 intl-positive isolates carried three different gene cassettes,while 21 isolates did not carry gene cassettes.The integrated gene cassettes were dfr and aadA confered resistance to trimethoprim and streptomycin,respectively.The main order of gene cassettes were dfrA1-tnpAIS26-aadA1(45/70).Statistical analysis showed that there was a significant correlation between integrons and multi-drug-resistance.PCR were employed to characterize the prevalence of the ESBL,PMQR,tetracycline-resistant genes,phenicol-resistant genes,16 S rRNA methylase genes.The results showed that 57.6% isolates carried ESBL and 46.2% isolates possessed PMQRgenes;the positive rates of tetracycline-resistant genes and phenicol-resistant genes were17.4% and 15.8%,separately.In addition,only one isolate carried 16 S rRNA methylase genes in the form of rmtB.Coexistence of different resistance genes was identified in 82 E.coli isolates.Twenty-six isolates carried three different genes,five isolates carried four genes and three carried five genes.Only one isolate harbored six genes.PFGE analysis showed that 91 class I-positive strains exhibited 63 patterns and no major cluster among these strains.In conclusion,resistance situation was serious in Hefei area where the detecting rates of ESBL,PMQR and classI integrons were high.PFGE patterns were distributed and no major cluster indicating that the strains had genetic polymorphisms.By investigating the drug resistance,prevalence of resistance genes and PFGE patterns,this study preliminary revealed that drug resistance genes played an important role in the development of multi-drug resistance,and provided a theoretical basis for guiding rational drug use in clinic,preventing and controlling the spread of disease and resistance genes.