Prevalence and Molecular Characteristics of Avian-Origin mcr-1-Harboring Escherichia coli in Shandong Province, China

Abstract

The objective of this study was to evaluate the prevalence and characteristics of avian-origin <i>mcr</i>-1-harbouring <i>Escherichia coli</i> in Shandong Province, China. During 2017-2018, a total of 668 non-duplicate <i>E. coli</i> isolates were separately collected from 8eight large intensive poultry farms in Shandong Province. Antimicrobial susceptibility testing for 10 antimicrobial agents commonly used in farms was performed on all <i>E. coli</i> isolates by the agar dilution method; the mobile colistin resistance gene (<i>mcr</i>-1) gene was screened by PCR, and <i>mcr</i>-1 positive isolates were PCR-screened for antimicrobial resistance genes and typed by multi-locus sequence typing (MLST). Among the 668 <i>E. coli</i>, 102 (15.3%) harbored the <i>mcr</i>-1 gene; high antimicrobial resistance rates were observed for ampicillin (100/102, 98.0%), followed by amoxicillin (99/102, 97.1%) and florfenicol (97/102, 95.1%), and a low level of resistance was found for amoxicillin/clavulanic acid (24/102, 23.5%). Five ESBL genes were detected, and all isolates carried <i>bla</i> _<i>TEM</i> (102/102, 100%), followed by <i>bla</i> _CTX-M (90/102, 88.2%). Four PMQR genes were detected; <i>aac(6)-Ib-cr</i> (40/102, 39.2%) was the most commonly isolated PMQR gene, followed by <i>qnrA</i> (10/102, 9.8%). Thirty-eight different kinds of STs were identified, and the dominant ST was ST93 (19/102, 18.6%), followed by ST48 (9/102, 8.8%). In summary, <i>E. coli</i> from poultry in Shandong could be a reservoir for the <i>mcr</i>-1 gene, which could pose serious risks to human public health.