The β-Lactamase Gene Profile and a Plasmid-Carrying Multiple Heavy Metal Resistance Genes of Enterobacter cloacae.

Chongyang Wu,Licheng Zhu,Hongmao Liu,Junwan Lu,Chaoqin Lin,Cong Cheng,Wangxiao Zhou,Yunliang Hu,Xinyi Zhu,Qiyu Bao

doi:10.1155/2018/4989602

Abstract

In this work, by high-throughput sequencing, antibiotic resistance genes, including class A (bla CTX-M, bla Z, bla TEM, bla VEB, bla KLUC, and bla SFO), class C (bla SHV, bla DHA, bla MIR, bla AZECL-29, and bla ACT), and class D (bla OXA) β-lactamase genes, were identified among the pooled genomic DNA from 212 clinical Enterobacter cloacae isolates. Six bla MIR-positive E. cloacae strains were identified, and pulsed-field gel electrophoresis (PFGE) showed that these strains were not clonally related. The complete genome of the bla MIR -positive strain (Y546) consisted of both a chromosome (4.78 Mb) and a large plasmid pY546 (208.74 kb). The extended-spectrum β-lactamases (ESBLs) (bla SHV-12 and bla CTX-M-9a) and AmpC (bla MIR) were encoded on the chromosome, and the pY546 plasmid contained several clusters of genes conferring resistance to metals, such as copper (pco), arsenic (ars), tellurite (ter), and tetrathionate (ttr), and genes encoding many divalent cation transporter proteins. The comparative genomic analyses of the whole plasmid sequence and of the heavy metal resistance gene-encoding regions revealed that the plasmid sequences of Klebsiella pneumoniae (such as pKPN-332, pKPN-3967, and pKPN-262) shared the highest similarity with those of pY546. It may be concluded that a variety of β-lactamase genes present in E. cloacae which confer resistance to β-lactam antibiotics and the emergence of plasmids carrying heavy metal resistance genes in clinical isolates are alarming and need further surveillance.

Highlights

Bacteria of the Enterobacter cloacae complex (ECC), which comprises six species, namely, E. cloacae, E. asburiae, E. hormaechei, E. kobei, E. ludwigii, and E. nimipressuralis [1], are widely distributed in nature
E. cloacae and E. hormaechei are most frequently isolated from human clinical specimens, and E. cloacae is among the Enterobacter sp. that have most commonly caused nosocomial infections in the last decade [2]
The resistance of E. cloacae to third-generation cephalosporins is caused by its overproduction of the AmpC β-lactamases when the production of this cephalosporinase is inducible in the presence of strong β-lactam antibiotics; treatment with thirdgeneration cephalosporins may promote the development of AmpC-overproducing mutants

Summary

Introduction

Bacteria of the Enterobacter cloacae complex (ECC), which comprises six species, namely, E. cloacae, E. asburiae, E. hormaechei, E. kobei, E. ludwigii, and E. nimipressuralis [1], are widely distributed in nature. E. cloacae and E. hormaechei are most frequently isolated from human clinical specimens, and E. cloacae is among the Enterobacter sp. E. cloacae has assumed clinical importance and has emerged as a major human pathogen; it accounts for up to 5% of hospital-acquired bacteremia cases, 5% of nosocomial pneumonia cases, 4% of nosocomial urinary tract infections, and 10% of postsurgical peritonitis cases [3]. The resistance of E. cloacae to third-generation cephalosporins is caused by its overproduction of the AmpC β-lactamases when the production of this cephalosporinase is inducible in the presence of strong β-lactam antibiotics (cefoxitin and imipenem); treatment with thirdgeneration cephalosporins may promote the development of AmpC-overproducing mutants. AmpC-producing organisms become resistant to almost all β-lactam antibiotics, with the exception of cefepime, cefpirome, and carbapenems

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