| With the use of antibiotics in animals as growth promoters or as therapeutic drugs over the last several decades, the rapidly increasing resistance levels of Escherichia coli (E.coli) in animals, especially multi-drug resistance(MDR) levels, has constituted a major challenge to antimicrobial discovery and chemotherapy, and represents a threat to human health.The aim of this study was to characterize the prevalence of extended-spectrum (3-lactamase (ESBL) genes and plasmid-mediated fluoroquinolone resistance (PMQR) determinants in E.coli isolates from chickens in Anhui Province, China, and molecular mechanism of transmission. Antimicrobial susceptibility for 12 antimicrobials,such as amoxicillin, amikacin, gentamicin, florfenicol, enrofloxacin and so on was determined by broth microdilution. Resistance rates varied among 12 antimicrobials. High rates of resistance to oxytetracycline (98.0%), amoxicillin (93.5%), doxycycline (90.6%), lomefloxacin (77.5%), ceftriaxome (70.3%), ofloxacin (68.8%), enrofloxacin (56.4%), and florfenicol (53.5%) were observed in the 202 E. coli isolates. Low rates of resistance to gentamicin (34.5%), apramycin (28.0%), ceftiofur (17.5%) and amikacin (8.4%) were observed. High rates of the multi-drug resistant (MDR) strains were observed. One hundred and forty-seven (72.8%) of the isolates were resistant to at least 6 antimicrobial agents, while 28 (13.9%) were resistant to at least 10 of these drugs.Polymerase chain reaction(PCR) and DNA sequencing were employed to characterize the molecular basis for ESBL (blaTEM,blaCTX-M,blaSHV) and PMQR {qnrA,qnrB,qnrC,qnrD,qnrS,aac(6’)-Ib-cr,qepA) genes. The prevalence of blaCTX-M, blaTEM-I and blaTEM-206 genes was 19.8%(40/202),24.3%(49/202) and 11.9%(24/202), respectively and no blaSHV genes were detected. Seventy-five out of the 202 (37.1%) isolates possessed a plasmid-mediated quinolone resistance determinant in the form of qnrS (n= 21); this determinant occurred occasionally in combination with aac(6’)-1b-cr (n= 65).No qnrA,qnrB,qnrC,qnrD and qepA genes were detected. Coexistence of ESBL and PMQR genes was identified in 31 of the isolates. Two E. coli isolates carried blaTEM-l, blaCTX-M and qnrS, while two others carried blaCTX-M, qnrS and aac(6’)-1b-cr. In addition, blaTEM-I qnrS and aac(6’)-1b-cr were co-located in two other E. coli isolates. To the best of our knowledge, this study is the first to describe detection of TEM-206-producing E. coli in farmed chickens, and the presence of blaTEM-206. qnrS and aac(6’)-1b-cr in one of the isolates.The 49 ESBL-and/or PMQR-positive isolates exhibited 43 major patterns. PFGE analysis showed that these isolates were genetically diverse. As the PFGE profiles did not show any major clusters among the four chicken farms, the clonal transfer of resistant strains was not present in these four farms.Our results indicated that resistance rates to β-lactams, tetracyclines and fluoroquinolones are high and the high prevalence of ESBL(49.5%) and PMQR(37.1%) genes in E.coli of poultry origin may be attributable to horizontal spread of these resistance determinants among E. coli. As the PFGE profiles did not show any major clusters among the four chicken farms, the clonal transfer of resistant strains was not present in these four farms. However, neither ESBL nor PMQR genes in E. coli isolates from chickens have been described in the Anhui Province. The main purpose of this study was to investigate the prevalence of ESBL and PMQR genes in E. coli collected recently from four chicken farms and characterization of the P-lactam and fluoroquinolone resistance mechanisms from isolates resistant to these drugs. To the best of our knowledge, this study is the first to describe detection of TEM-206-producing E. coli in farmed chickens, and the presence of blaTEM-206, qnrS and aac(6’)-1b-cr in one of the isolates.This study provides basis of controling the resistance to β-lactams and fluoroquinolones of E.coli and molecular mechanism of transmission of ESBL and PMQR genes.It also provides guidance for clinical veterinarian to select antimicrobials rationally... |
