AUTHOR=Zhang Enbao , Zong Shuaizhou , Zhou Wei , Zhou Jinzhi , Han Jianzhong , Qu Daofeng 

TITLE=Characterization and comparative genomics analysis of RepA_N multi-resistance plasmids carrying optrA from Enterococcus faecalis

JOURNAL=Frontiers in Microbiology

VOLUME=13

YEAR=2023

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2022.991352

DOI=10.3389/fmicb.2022.991352

ISSN=1664-302X

ABSTRACT=<sec><title>Introduction</title><p>This research aimed to investigate the antibiotic resistance of <italic>Enterococcus faecalis</italic> from swine farms in Zhejiang Province and the prevalence and transmission mechanism of oxazolidone resistance gene <italic>optrA</italic>.</p></sec><sec><title>Method</title><p>A total of 226 <italic>Enterococcus faecalis</italic> were isolated and their resistance to 14 antibiotics was detected by broth microdilution. The resistance genes were detected by PCR.</p></sec><sec><title>Results</title><p>The antibiotic resistance rate of 226 isolates to nearly 57% (8/14) of commonly used antibiotics was higher than 50%. The resistance rate of tiamulin was highest (98.23%), that of tilmicosin, erythromycin, tetracycline and florfenicol was higher than 80%, and that of oxazolidone antibiotic linezolid was 38.49%. The overall antibiotics resistance in Hangzhou, Quzhou and Jinhua was more serious than that in the coastal cities of Ningbo and Wenzhou. The result of PCR showed that <italic>optrA</italic> was the main oxazolidinone and phenicols resistance gene, with a detection rate of 71.68%, and <italic>optrA</italic> often coexisted with <italic>fexA</italic> in the isolates. Through multi-locus sequence typing, conjugation transfer, and replicon typing experiments, it was found that the horizontal transmission mediated by RepA_N plasmid was the main mechanism of <italic>optrA</italic> resistance gene transmission in E. faecalis from Zhejiang Province. Two conjugative multi-resistance plasmids carrying <italic>optrA</italic>, RepA_N plasmid pHZ318-<italic>optrA</italic> from Hangzhou and Rep3 plasmid from Ningbo, were sequenced and analyzed. pHZ318-<italic>optrA</italic> contain two multidrug resistance regions (MDR), which contributed to the MDR profile of the strains. <italic>optrA</italic> and <italic>fexA</italic> resistance genes coexisted in IS<italic>1216</italic>E-<italic>fexA</italic>-<italic>optrA</italic>-<italic>ferr</italic>-<italic>erm</italic>(A)-IS<italic>1216</italic>E complex transposon, and there was a partial sequence of Tn<italic>554</italic> transposon downstream. However, pNB304-optrA only contain <italic>optrA</italic>, <italic>fexA</italic> and an insertion sequence IS<italic>Vlu1</italic>. The presence of mobile genetic elements at the boundaries can possibly facilitate transfer among <italic>Enterococcus</italic> through inter-replicon gene transfer.</p></sec><sec><title>Discussion</title><p>This study can provide theoretical basis for ensuring the quality and safety of food of animal origin, and provide scientific guidance for slowing down the development of multi-antibiotic resistant <italic>Enterococcus</italic>.</p></sec>