Abstract
The emergence of extended-spectrum cephalosporin (ESC)-resistant Gram-negative bacteria is of great concern in both human and veterinary medicine. The aim of this study was to investigate ESC-resistant bacterial isolates from companion animals in South Korea between 2017 and 2019. Isolates with ESC resistance genes, which were identified by PCR, were assessed for genetic relatedness by multi-locus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE). In total, 91 ESC-resistant Escherichia coli, Klebsiella spp., Serratia spp., and Enterobacter cloacae isolates harbored the blaTEM gene. Among other ESC resistance genes, blaCTX-M-15, blaCIT, and blaCTX-M-55 were predominantly detected in E. coli isolates, whereas blaSHV and blaDHA were more frequently detected in Klebsiella pneumoniae isolates. In addition, all blaEBC-positive isolates were classified as E. cloacae. From the MLST results, blaCTX-M-9-carrying ST131, blaCIT-carrying ST405, and blaCTX-M-1-carrying ST3285 strains were dominant among E. coli isolates. ST273 and ST275 strains harboring blaSHV were frequently detected in K. pneumoniae isolates. Various sequence types were obtained in E. cloacae and Klebsiella oxytoca isolates. All isolates demonstrated unique PFGE profiles (<57–98% similarity) and were unlikely to be derived from a single clone. The present study reveals the presence and wide genetic distribution of ESC-resistant bacterial species in South Korean companion animals.
Highlights
The emergence and prevalence of β-lactam resistance in Gram-negative bacteria has increased consistently over the past few decades [1,2]
extended-spectrum cephalosporin (ESC) resistance is mainly caused by the expression of extended-spectrum β-lactamase (ESBL) and AmpC β-lactamase (AmpC) genes that are normally encoded on mobile genetic elements, mostly plasmids [1]
Among the 91 ESC-resistant Enterobacterales isolates analyzed in this study, all of the isolates harbored the blaTEM gene. blaCTX-M (n = 42, 82.4%) was abundantly detected in E. coli isolates, whereas blaSHV (n = 16, 94.1%) was mainly detected in Klebsiella pneumoniae isolates (Table 1)
Summary
The emergence and prevalence of β-lactam resistance in Gram-negative bacteria has increased consistently over the past few decades [1,2]. Resistance to β-lactams is mostly caused by bacterially produced β-lactamases that hydrolyze and inactivate extendedspectrum cephalosporins (ESCs), such as third and fourth generation cephalosporins [1]. ESC resistance is mainly caused by the expression of extended-spectrum β-lactamase (ESBL) and AmpC β-lactamase (AmpC) genes that are normally encoded on mobile genetic elements, mostly plasmids [1]. The first ESBLs have evolved from the native β-lactamases TEM and SHV via genetic mutations [3]. CTX-M β-lactamases, a new group of plasmid-mediated ESBLs, were first reported in Japan in 1986 [4]. Since 2000, CTX-M β-lactamases have increasingly been reported in both human and animal populations and are the dominant type of ESBL, replacing classical TEM- and SHV-type ESBLs in most areas of the world [5]
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