Abstract
Extended-spectrum β-lactamases (ESBLs) production and (fluoro)quinolone (FQ) resistance among Salmonella pose a public health threat. The objective of this study was the phenotypic and genotypic characterization of an ESBL-producing and nalidixic acid-resistant Salmonella enterica serovar Gloucester isolate (serotype 4:i:l,w) of sequence type 34 (ST34) from ready-to-eat (RTE) meat products in China. Whole-genome short and long read sequencing (HiSeq and MinION) results showed that it contained blaCTX–M–55, qnrS1, and tetB genes, with blaCTX–M–55 and qnrS1 located in chromosomal IS26-mediated composite transposon (IS26–qnrS1–IS3–Tn3–orf–blaCTX–M–55–ISEcp1–IS26). The same genetic structure was found in the chromosome of S. enterica subsp. enterica serovar Typhimurium strain and in several plasmids of Escherichia coli, indicating that the IS26-mediated composite transposon in the chromosome of S. Gloucester may originate from plasmids of E. coli and possess the ability to disseminate to Salmonella and other bacterial species. Besides, the structural unit qnrS1–IS3–Tn3–orf–blaCTX–M–55 was also observed to be linked with ISKpn19 in both the chromosomes and plasmids of various bacteria species, highlighting the contribution of the insertion sequences (IS26 and ISKpn19) to the co-dissemination of blaCTX–M–55 and qnrS1. To our knowledge, this is the first description of chromosomal blaCTX–M–55 and qnrS in S. Gloucester from RTE meat products. Our work expands the host range and provides additional evidence of the co-transfer of blaCTX–M–55 and qnrS1 among different species of Salmonella through the food chain.
Highlights
Salmonella enterica is a leading cause of global bacterial foodborne gastroenteritis (Kirk et al, 2015; Lokken et al, 2016)
The blaCTX−M−55 and qnrS1 genes were located on chromosome within 8,993 bp composite transposon, IS26– qnrS1–IS3–Tn3–orf –blaCTX−M−55–ISEcp1–IS26, and flanked by genes encoding DNA cytosine methyltransferase, type II site-specific deoxyribonuclease, hypothetical protein, 3 –5 exoribonuclease, DUF4224 domain-containing protein, and tyrosine-type recombinase/integrase. blaCTX−M−55 was linked with incomplete ISEcp1
The structural unit qnrS1–IS3–Tn3–orf –blaCTX−M−55 was observed in various bacterial species, such as the chromosome of E. coli strains and plasmids in E. coli, Klebsiella pneumoniae, Salmonella Typhi, and S. enterica (Figure 1 and Supplementary Table 2)
Summary
Salmonella enterica is a leading cause of global bacterial foodborne gastroenteritis (Kirk et al, 2015; Lokken et al, 2016). Cephalosporin resistance is mediated predominantly by extended-spectrum β-lactamases (ESBLs), AmpC β-lactamases, and carbapenemase (Arlet et al, 2006). These β-lactamases confer resistance to a wide range of β-lactam antibiotics, including penicillins, cephalosporins, and carbapenems. They are typically associated with multiple antibiotic resistance, such as quinolones, aminoglycosides, chloramphenicol, tetracycline, and trimethoprim–sulfamethoxazole and can transfer together among different bacteria species via mobile genetic elements (MGEs), leaving few therapeutic choices (Thomson, 2010; Iwamoto et al, 2017; Qiao et al, 2017; Nadimpalli et al, 2019)
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