The <i>β</i>-Lactamase Gene Profile and a Plasmid-Carrying Multiple Heavy Metal Resistance Genes of <i>Enterobacter cloacae</i>

Abstract

In this work, by high-throughput sequencing, antibiotic resistance genes, including class A (<i>bla</i> _CTX-M, <i>bla</i> _Z, <i>bla</i> _TEM, <i>bla</i> _VEB, <i>bla</i> _KLUC, and <i>bla</i> _SFO), class C (<i>bla</i> _SHV, <i>bla</i> _DHA, <i>bla</i> _MIR, <i>bla</i> _AZECL-29, and <i>bla</i> _ACT), and class D (<i>bla</i> _OXA) <i>β</i>-lactamase genes, were identified among the pooled genomic DNA from 212 clinical <i>Enterobacter cloacae</i> isolates. Six <i>bla</i> _MIR-positive <i>E. cloacae</i> strains were identified, and pulsed-field gel electrophoresis (PFGE) showed that these strains were not clonally related. The complete genome of the <i>bla</i> _MIR <i>-</i>positive strain (Y546) consisted of both a chromosome (4.78 Mb) and a large plasmid pY546 (208.74 kb). The extended-spectrum <i>β</i>-lactamases (ESBLs) (<i>bla</i> _SHV-12 and <i>bla</i> _CTX-M-9a) and AmpC (<i>bla</i> _MIR) were encoded on the chromosome, and the pY546 plasmid contained several clusters of genes conferring resistance to metals, such as copper (<i>pco</i>), arsenic (<i>ars</i>), tellurite (<i>ter</i>), and tetrathionate (<i>ttr</i>), 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 <i>Klebsiella pneumoniae</i> (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 <i>β</i>-lactamase genes present in <i>E. cloacae</i> which confer resistance to <i>β</i>-lactam antibiotics and the emergence of plasmids carrying heavy metal resistance genes in clinical isolates are alarming and need further surveillance.