Genetic and drug susceptibility profiles of mcr-1-bearing foodborne Salmonella strains collected in Shenzhen, China during the period 2014-2017

Comprehensive genomic and plasmid characterization of multidrug-resistant bacterial strains by R10.4.1 nanopore sequencing

The escalating prevalence of multidrug-resistant (MDR) bacteria pose a significant public health threat. Understanding the genomic features and deciphering the antibiotic resistance profiles of these pathogens is crucial for development of effective surveillance and treatment strategies. In this study, we employed the R10.4.1 nanopore sequencing technology, specifically through the use of the MinION platform, to analyze eight MDR bacterial strains originating from clinical, ecological and food sources. A single 72-hour sequencing run could yield approximately 12 million reads which covered a total of 34 gigabases (Gbp). The nanopore R10.4.1 data was processed using the Flye assembler, successfully assembling the genomes of eight bacterial strains and their 18 plasmids. Notably, the assemblies generated solely from R10.4.1 nanopore data closely matched those from next-generation sequencing data. Diverse antibiotic resistance patterns and specific resistance genes in the test strains were identified. Hospital strains that exhibited multidrug resistance were found to harbor various resistance genes that encode efflux pumps and extended-spectrum β-lactamases. Environmental and food sources were found to display resistance profiles in a species-specific manner. The composition of structurally complex plasmids in the test strains could also be revealed by analysis of nanopore long reads, which also suggested evidence of horizontal transfer of plasmids between different bacterial species. These findings provide valuable insights into the genetic characteristics of MDR bacteria and demonstrating the practicality of nanopore sequencing technology for detecting of resistance elements in bacterial pathogens.

Integrating metagenomic and isolation strategies revealed high contamination of pathogenies and resistome in market shrimps

This study employs a comprehensive approach combining metagenomic analysis and bacterial isolation to elucidate the microbial composition, antibiotic resistance genes (ARGs), and virulence factors (VFGs) present in shrimps from market and supermarket. Metagenomic analysis of shrimps revealed a dominance of Proteobacteria and Bacteroidetes with Firmicutes notably enriched in some samples. On the other hand, the dominant bacteria isolated included Citrobacter portucalensis, Escherichia coli, Salmonella enterica, Vibrio species and Klebsiella pneumonaie. Metagenomic analysis unveiled a diverse spectrum of 23 main types and 380 subtypes of ARGs in shrimp samples including many clinical significant ARGs such as blaKPC, blaNDM, mcr, tet(X4) etc. Genomic analysis of isolated bacterial strains identified 14 ARG types with 109 subtype genes, which complemented the metagenomic data. Genomic analysis also allowed us to identify a rich amount of MDR plasmids, which provided further insights into the dissemination of resistance genes in different species of bacteria in the same samples. Examination of VFGs and mobile genetic elements (MGEs) in both metagenomic and bacterial genomes revealed a complex landscape of factors contributing to bacterial virulence and genetic mobility. Potential co-occurrence patterns of ARGs and VFGs within human pathogenic bacteria underlined the intricate interplay between antibiotic resistance and virulence. In conclusion, this integrated analysis for the first time provides a comprehensive view and sheds new light on the potential hazards associated with shrimp products in the markets. The findings underscore the necessity of ongoing surveillance and intervention strategies to mitigate risks posed by antibiotic-resistant bacteria in the food supply chain using the novel comprehensive approaches.

Characteristics of Two mcr-1-Harboring IncHI2 Plasmids from Clinical Salmonella Isolates in Jiaxing City

Salmonella is a primary cause of foodborne diseases, and the increasing prevalence of mcr-1-carrying plasmids, which confer colistin resistance to Salmonella, poses significant global health concerns. As the frequency of occurrence of the mcr-1 gene is increasing globally, we studied the prevalence of mcr-1 in clinical Salmonella isolates by analyzing 195 clinical strains isolated in 2020. Of the 195 Salmonella isolates, 41 isolates were resistant to colistin. We found mcr-1 in two strains (Salmonella Typhimurium ZJJX20006 and Salmonella Kentucky ZJJX20014), which we analyzed in detail via whole-genome sequencing and antibiotic susceptibility testing. Two strains displayed resistance to ampicillin, ampicillin-sulbactam, tetracycline, chloramphenicol, and cotrimoxazole, while ZJJX20006 displayed resistance to colistin and ZJJX20014 was sensitive. Genomic analysis revealed that these strains had plasmid-encoded mcr-1 in IncHI2 plasmids, which were not similar to the mcr-1-IncX4 identified in 2016. These two strains also harbored other drug resistance genes, including blaOXA-1 and blaCTX-M-14. Our findings may help clarify the molecular mechanisms of mcr-1 dissemination among Salmonella strains in Jiaxing City and offer insights into the evolution of mcr-1 in Salmonella.

Efficient screening of adsorbed receptors for Salmonella phage LP31 and identification of receptor-binding protein

The adsorption process is the first step in the lifecycle of phages and plays a decisive role in the entire infection process. Identifying the adsorption mechanism of phages not only makes phage therapy more precise and efficient but also enables the exploration of other potential applications and modifications of phages. Phage LP31 can lyse multiple Salmonella serotypes, efficiently clearing biofilms formed by Salmonella enterica serovar Enteritidis (S. Enteritidis) and significantly reducing the concentration of S. Enteritidis in chicken feces. Therefore, LP31 has great potential for many practical applications. In this study, we established an efficient screening method for phage infection-related genes and identified a total of 10 genes related to the adsorption process of phage LP31. After the construction of strain C50041ΔrfaL 58-358, it was found that the knockout strain had a rough phenotype as an O-antigen-deficient strain. Adsorption rate and transmission electron microscopy experiments showed that the receptor for phage LP31 was the O9 antigen of S. Enteritidis. Homology comparison and adsorption experiments confirmed that the tail fiber protein Lp35 of phage LP31 participated in the adsorption process as a receptor-binding protein. IMPORTANCE A full understanding of the interaction between phages and their receptors can help with the development of phage-related products. Phages like LP31 with the tail fiber protein Lp35, or a closely related protein, have been reported to effectively recognize and infect multiple Salmonella serotypes. However, the role of these proteins in phage infection has not been previously described. In this study, we established an efficient screening method to detect phage adsorption to host receptors. We found that phage LP31 can utilize its tail fiber protein Lp35 to adsorb to the O9 antigen of S. Enteritidis, initiating the infection process. This study provides a great model system for further studies of how a phage-encoded receptor-binding protein (RBP) interacts with its host's RBP binding target, and this new model offers opportunities for further theoretical and experimental studies to understand the infection mechanism of phages.

The characteristics of mcr-bearing plasmids in clinical Salmonella enterica in Sichuan, China, 2014 to 2017

Salmonella is one of the most important zoonotic pathogens and a major cause of foodborne illnesses, posing a serious global public health hazard. The emergence of plasmid-mediated mcr genes in Salmonella has greatly reduced the clinical choice of salmonellosis treatment. The aim of this study was to investigate the plasmid characteristics of mcr-positive Salmonella identified from patients in Sichuan, China during 2014 to 2017 by whole genomes sequencing. In this study, a total of 12 mcr-positive isolates (1.15%, ; mcr-1, n=10; mcr-3, n=2) were identified from 1046 Salmonella isolates using PCR. Further characterization of these isolates was performed through antimicrobial susceptibility testing, conjugation assays, whole genome sequencing, and bioinformatics analysis. The mcr-1 gene in these isolates were carried by three types of typical mcr-1-bearing plasmids widely distributed in Enterobacteriaceae (IncX4, IncI2 and IncHI2). Of note, two mcr-1-harboring IncHI2 plasmids were integrated into chromosomes by insertion sequences. Two mcr-3-bearing plasmids were IncC and IncFIB broad-host-range plasmids respectively. Genetic context analysis found that mcr-1 was mainly located in Tn6330 or truncated Tn6300, and mcr-3 shared a common genetic structure tnpA-mcr-3-dgkA-ISKpn40. Overall, we found that mcr gene in clinical Salmonella were commonly carried by broad-host plasmids and have potential to transfer into other bacteria by these plasmids. Continuous surveillance of MDR Salmonella in humans and investigation the underlying transmission mechanisms of ARGs are vital to curb the current severe AMR concern.

Farm to table: colistin resistance hitchhiking through food

Colistin is a high priority, last-resort antibiotic recklessly used in livestock and poultry farms. It is used as an antibiotic for treating multi-drug resistant Gram-negative bacterial infections as well as a growth promoter in poultry and animal farms. The sub-therapeutic doses of colistin exert a selection pressure on bacteria leading to the emergence of colistin resistance in the environment. Colistin resistance gene, mcr are mostly plasmid-mediated, amplifying the horizontal gene transfer. Food products such as chicken, meat, pork etc. disseminate colistin resistance to humans through zoonotic transfer. The antimicrobial residues used in livestock and poultry often leaches to soil and water through faeces. This review highlights the recent status of colistin use in food-producing animals, its association with colistin resistance adversely affecting public health. The underlying mechanism of colistin resistance has been explored. The prohibition of over-the-counter colistin sales and as growth promoters for animals and broilers has exhibited effective stewardship of colistin resistance in several countries.

Carriage and Transmission of mcr-1 in Salmonella Typhimurium and Its Monophasic 1,4,[5],12:i:- Variants from Diarrheal Outpatients: a 10-Year Genomic Epidemiology in Guangdong, Southern China

The banning of colistin as a feed additive for food-producing animals in mainland China in 2017 caused the decline in the prevalence of Escherichia coli-mobilized colistin resistance (mcr-1) in China. Salmonella Typhimurium and its monophasic 1,4,[5],12:i:- variants are also the main species associated with the spread of mcr-1; however, the evidence of the prevalence and transmission of mcr-1 among Salmonella is lacking. Herein, the 5,354 Salmonella isolates recovered from fecal samples of diarrheal patients in Guangdong, Southern China, from 2009 to 2019 were screened for colistin resistance and mcr-1, and mcr-1-positive isolates were characterized based on whole-genome sequencing (WGS) data. Relatively high prevalence rates of colistin resistance and mcr-1 (4.05%/4.50%) were identified, and more importantly, the prevalence trends of colistin-resistant and mcr-1-positive Salmonella isolates had a similar dynamic profile, i.e., both were first detected in 2012 and rapidly increased during 2013 to 2016, followed by a sharp decrease since 2017. WGS and phylogenetic analysis indicate that, whether before or after the ban, the persistence and cross-hospital transmission of mcr-1 are primarily determined by IncHI2 plasmids with similar backbones and sequence type 34 (ST34) Salmonella in specific clades that are associated with a high prevalence of IncHI2 plasmids and clinically important antimicrobial resistance genes, including bla_CTX-M-14-fosA3-oqxAB-floR genotypes. Our work reveals the difference in the prevalence rate of mcr-1 in clinical Salmonella before and after the Chinese colistin ban, whereas mcr-1 transmission was closely linked to multidrug-resistant IncHI2 plasmid and ST34 Salmonella across diverse hospitals over 10 years. Continued surveillance is required to explore the factors related to a sharp decrease in mcr-1 after the recent ban and determine whether the ban has affected the carriage of mcr-1 in Salmonella circulating in the health care system. IMPORTANCE Colistin is one of the last-line antibiotics for the clinical treatment of Enterobacteriaceae. However, the emergence of the mobilized colistin resistance (mcr-1) gene has spread throughout the entire human health system and largely threatens the usage of colistin in the clinical setting. In this study, we investigated the existence of mcr-1 in clinical Salmonella from a 10-year continuous surveillance and genomic study. Overall, the colistin resistance rate and mcr-1 carriage of Salmonella in tertiary hospitals in Guangdong (2009 to 2019) were relatively high and, importantly, rapidly increased from 2013 to 2016 and significantly decreased after the Chinese colistin withdrawal. However, before or after the ban, the MDR IncHI2 plasmid with a similar backbone and ST34 Salmonella were the main vectors involved in the spread of mcr-1. Interestingly, these Chinese mcr-1-carrying Salmonella obtain phylogenetically and phylogeographically distinct patterns compared with those from other continents and are frequently associated with clinically important ARGs including the extended-spectrum β-lactamases. Our data confirmed that the national stewardship intervention seems to be successful in blocking antibiotic resistance determinants and that continued surveillance of colistin resistance in clinical settings, farm animals, and related products is necessary.