Epidemiologic and genomic insights on mcr-1-harbouring Salmonella from diarrhoeal outpatients in Shanghai, China, 2006–2016

Abstract

Background Colistin resistance mediated by mcr-1 -harbouring plasmids is an emerging threat in Enterobacteriaceae, like Salmonella . Based on its major contribution to the diarrhoea burden, the epidemic state and threat of mcr-1 -harbouring Salmonella in community-acquired infections should be estimated. Methods This retrospective study analysed the mcr-1 gene incidence in Salmonella strains collected from a surveillance on diarrhoeal outpatients in Shanghai Municipality, China, 2006–2016. Molecular characteristics of the mcr-1 -positive strains and their plasmids were determined by genome sequencing. The transfer abilities of these plasmids were measured with various conjugation strains, species, and serotypes. Findings Among the 12,053 Salmonella isolates, 37 mcr-1 -harbouring strains, in which 35 were serovar Typhimurium, were detected first in 2012 and with increasing frequency after 2015. Most patients infected with mcr-1 -harbouring strains were aged <5 years. All strains, including fluoroquinolone-resistant and/or extended-spectrum β-lactamase-producing strains, were multi-drug resistant. S. Typhimurium had higher mcr-1 plasmid acquisition ability compared with other common serovars. Phylogeny based on the genomes combined with complete plasmid sequences revealed some clusters, suggesting the presence of mcr-1 -harbouring Salmonella outbreaks in the community. Most mcr-1 -positive strains were clustered together with the pork strains, strongly suggesting pork consumption as a main infection source. Interpretation The mcr-1 -harbouring Salmonella prevalence in community-acquired diarrhoea displays a rapid increase trend, and the ESBL -mcr-1 -harbouring Salmonella poses a threat for children. These findings highlight the necessary and significance of prohibiting colistin use in animals and continuous monitoring of mcr-1 -harbouring Salmonella .

Genomic Characterization of mcr-1-carrying Salmonella enterica Serovar 4,[5],12:i:- ST 34 Clone Isolated From Pigs in China

“…All mcr-1-positive S. enterica 4,[5],12:i:-strains, belonging to ST34, were often related to an evolving multidrug-resistant S. enterica 4,[5],12:i:-clade in Australia, China, Italy, and United States (Li et al, 2016;Alicia et al, 2018;Elnekave et al, 2018). It is likely that the clonal dissemination of S. enterica 4,[5],12:i:-ST34 contributes to the spread of the mcr-1 gene among food animals in China (Lu et al, 2019) and may become a global significant public health concern (Elnekave et al, 2018;Mather et al, 2018;Monte et al, 2019).…”

Characterization of Salmonella Resistome and Plasmidome in Pork Production System in Jiangsu, China

“…Previous reports showed that the prevalence of mcr-1 gene was quite infrequent in Salmonella. Among the 12,053 Salmonella isolates in China (2006-2016), the mcr-1 gene was found only in 37 strains, out of which 35 strains were S. Typhimurium, and the remaining two strains were S. Enteritidis and S. Wandsworth (43,44).…”

Carriage of Distinct mcr‐1‐Harboring Plasmids by Unusual Serotypes of Salmonella

“…The increasing host range of mcr‐1 ‐harboring plasmid in Salmonella strains were found in Homo sapiens , food, and livestock and poultry in recent years in China,18,23,29,30 which further increased the risk of antibiotic resistance to public health. In this study, two strains isolated from ducks harbored mcr‐1 ‐bearing plasmids, while none was isolated from chicken or pig, which is different from the previous study that pig and chicken farms had the highest isolation rate of mcr‐1 ‐carrying strains 12,13.…”