Phenotypic and Genotypic Characterization of Multidrug-Resistant Enterobacter hormaechei Carrying <i>qnrS</i> Gene Isolated from Chicken Feed in China

Abstract

Multidrug resistance (MDR) in Enterobacteriaceae including resistance to quinolones is rising worldwide. The plasmid-mediated quinolone resistance (PMQR) gene <i>qnrS</i> is prevalent in Enterobacteriaceae. However, the <i>qnrS</i> gene is rarely found in Enterobacter hormaechei (<i>E. hormaechei</i>). Here, we reported one multidrug resistant <i>E. hormaechei</i> strain M1 carrying the <i>qnrS1</i> and <i>bla</i>_TEM-1 genes. This study was to analyze the characteristics of MDR <i>E. hormaechei</i> strain M1. The <i>E. hormaechei</i> strain M1 was identified as Enterobacter cloacae complex by biochemical assay and 16S rRNA sequencing. The whole genome was sequenced by the Oxford Nanopore method. Taxonomy of the <i>E. hormaechei</i> was based on multilocus sequence typing (MLST). The <i>qnrS</i> with the other antibiotic resistance genes were coexisted on IncF plasmid (pM1). Besides, the virulence factors associated with pathogenicity were also located on pM1. The <i>qnrS1</i> gene was located between insertion element IS2A (upstream) and transposition element ISKra4 (downstream). The comparison result of IncF plasmids revealed that they had a common plasmid backbone. Susceptibility experiment revealed that the <i>E. hormaechei</i> M1 showed extensive resistance to the clinical antimicrobials. The conjugation transfer was performed by filter membrane incubation method. The competition and plasmid stability assays suggested the host bacteria carrying <i>qnrS</i> had an energy burden. As far as we know, this is the first report that <i>E. hormaechei</i> carrying <i>qnrS</i> was isolated from chicken feed. The chicken feed and poultry products could serve as a vehicle for these MDR bacteria, which could transfer between animals and humans through the food chain. We need to pay close attention to the epidemiology of <i>E. hormaechei</i> and prevent their further dissemination. <b>IMPORTANCE</b> Enterobacter hormaechei is an opportunistic pathogen. It can cause infections in humans and animals. Plasmid-mediated quinolone resistance (PMQR) gene <i>qnrS</i> can be transferred intergenus, which is leading to increase the quinolone resistance levels in Enterobacteriaceae. Chicken feed could serve as a vehicle for the MDR <i>E. hormaechei</i>. Therefore, antibiotic-resistance genes (ARGs) might be transferred to the intestinal flora after entering the gastrointestinal tract with the feed. Furthermore, antibiotic-resistant bacteria (ARB) were also excreted into environment with feces, posing a huge threat to public health. This requires us to monitor the ARB and antibiotic-resistant plasmids in the feed. Here, we demonstrated the characteristics of one MDR <i>E. hormaechei</i> isolate from chicken feed. The plasmid carrying the <i>qnrS</i> gene is a conjugative plasmid with transferability. The presence of plasmid carrying antibiotic-resistance genes requires the maintenance of antibiotic pressure. In addition, the <i>E. hormaechei</i> M1 belonged to new sequence type (ST). These data show the MDR <i>E. hormaechei</i> M1 is a novel strain that requires our further research.