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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 IS 26 -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. [ABSTRACT FROM AUTHOR]

Objectives: Our aim was to determine the antimicrobial susceptibilities of 2862 Listeria monocytogenes cultured from various foods in China and to use WGS to characterize the antimicrobial resistance and virulence genotypes of those expressing a resistance phenotype.Methods: The susceptibilities of 2862 L. monocytogenes were determined by broth microdilution. Twenty-eight L. monocytogenes were found to be resistant to one to four antibiotics. All 28 resistant isolates were subsequently sequenced using short-read high accuracy protocols. The corresponding genomes were assembled and further analysis was carried out using appropriate bioinformatics pipelines.Results: All 28 resistant L. monocytogenes were classified into five STs (ST3, ST8, ST9, ST155 and ST515). Both ST9 and ST155 were dominant and their genotypes correlated with their resistance phenotypes. All ST9 isolates were MDR and could be phylogenetically classified into two clusters. One was relatively close to clinical origins and one to food. Downstream analysis of the genetic contexts in which these resistance genotypes were found suggested that these may have been acquired from other bacteria by horizontal transfer or insertion into the chromosome. All isolates harboured Listeria pathogenicity island (LIPI)-1 and LIPI-2, and only two harboured LIPI-3.Conclusions: This study reported on the antimicrobial susceptibilities of 2862 foodborne L. monocytogenes along with the genomic characterization of 28 resistant isolates, 11 of which expressed an MDR phenotype. These data showed that this bacterium can acquire resistance by horizontal gene transfer in and between species. This study may necessitate a re-evaluation of risk to public health, associated with this bacterial species. [ABSTRACT FROM AUTHOR]

Shiga toxin-producing Escherichia coli (STEC) O157 is an important foodborne pathogen. The aims of this study were to determine genetic relatedness of STEC O157 isolated from foods in China. STEC O157 isolates from food were characterized by virulence gene typing, antibiotyping, Multi-locus sequence typing (MLST), pulsed-field gel electrophoresis analysis (PFGE), Multi-locus variable number tandem repeat analysis (MLVA), and the single nucleotide polymorphism (SNP) clade typing. Of the 30 STEC O157 isolates analyzed, all isolates harbored eae , exhA , stx1 and/or stx2 genes with stx2c subtype predominating. By MLST, they were relatively homogenous with only 4 STs. PFGE and MLVA generated 22 pulsotyples and 23 patterns, respectively, which showed considerable diversity. Only one clade 8 isolate was detected. These results indicate that STEC O157 isolates from foods in China were heterogeneous. There was no correlation between genotypic characteristics and sources of isolates. Since different subtyping methods often give different discriminatory powers, the use of more than one subtyping approach is necessary in providing a more accurate picture of the genetic diversity of STEC O157. Four isolates were from ready-to-eat meat or salads, underscores the risk of infections. There is a need for surveillance of STEC O157 in foods and clinically and implementation of prevention strategies to prevent outbreaks of STEC O157 infections in China. [ABSTRACT FROM AUTHOR]