Abstract
The mcr-1 gene mediating mobile colistin resistance in Escherichia coli was first reported in China in 2016 followed by reports among different species worldwide, especially in E. coli and Klebsiella. However, data on its transmission in Salmonella are still lacking. This study analyzed the antimicrobial resistance (AMR) profiles and the mcr-1 gene presence in 755 foodborne Salmonella from 26 provinces of mainland, China in 2016. Genomic features of two mcr-1-carrying isolates, genome sequencing, serotypes and further resistance profiles were studied. Among the 755 Salmonella tested, 72.6% were found to be resistant to at least one antimicrobial agent and 10% were defined as multi-drug resistant (MDR). Salmonella Derby CFSA231 and Salmonella Typhimurium CFSA629 were mcr-1-harboring isolates. Both expressed an MDR phenotype and included a single circular chromosome and one plasmid. Among the 22 AMR genes identified in S. Derby CFSA231, only the mcr-1 gene was localized on the IncX4 type plasmid pCFSA231 while 20 chromosomal AMR genes, including four plasmid-mediated quinolone resistance (PMQR) genes, were mapped within a 64 kb Salmonella genomic island (SGI) like region. S. Typhimurium CFSA629 possessed 11 resistance genes including an mcr-1.19 variant and two ESBL genes. Two IS26-flanked composite-like transposons were identified. Additionally, 153 and 152 virulence factors were separately identified in these two isolates with secretion system and fimbrial adherence determinants as the dominant virulence classes. Our study extends our concern on mcr-1-carrying Salmonella in regards to antimicrobial resistance and virulence factors, and highlight the importance of surveillance to mitigate dissemination of mcr-encoding genes among foodborne Salmonella.
Highlights
MATERIALS AND METHODSSalmonella, one of the top-ranking foodborne pathogens worldwide, is known to cause mild to severe foodborne infections, and has posed a significant public health challenge globally (Jazeela et al, 2020)
We identified a number of similar well conserved plasmids differing by less than 4 nucleotides by BLAST on National Center for Biotechnology Information (NCBI), and all of which were distributed in Enterobacteriaceae, with a high number of these (>80%) being associated with E. coli
Salmonella are important foodborne zoonotic pathogens often linked to cases of gastroenteritis and bacteremia, and are one of the leading causes of global bacterial food poisoning worldwide (Threlfall, 2002)
Summary
MATERIALS AND METHODSSalmonella, one of the top-ranking foodborne pathogens worldwide, is known to cause mild to severe foodborne infections, and has posed a significant public health challenge globally (Jazeela et al, 2020). Antimicrobial compounds are used to treat both human infections and food animal production and evidence suggests that antimicrobial use in food-producing animals contributes to resistance among foodborne Salmonella (Crump et al, 2011). This usage increases the risk of failure when clinical treatment measures are platformed (Bai et al, 2016). Colistin (polymyxin E) is considered to be an antimicrobial agent of last-resort for treatment of MDR Gram-negative bacterial infections (Elbediwi et al, 2019). Based on literature review in public scientific databases, mcr-like genes are reported at lower rates in Salmonella when compared to E. coli, there have been increased reported numbers of mcr-mediated colistin resistance in Salmonella spp. from humans, animals, and foods after 2016 (Li et al, 2016; Sun et al, 2018; Lima et al, 2019; Borowiak et al, 2020; Sia et al, 2020)
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