Genetic Characterization of mcr-1-Positive Multidrug-Resistant Salmonella enterica Serotype Typhimurium Isolated From Intestinal Infection in Children and Pork Offal in China

The prevalent dynamic and genetic characterization of mcr-1 encoding multi-drug resistant Escherichia coli strains recovered from poultry in Hebei, China

OBJECTIVES

Colistin is known as the last resort antibiotic to treat the infections caused by multi-drug resistant (MDR) foodborne pathogens. The emergence and widespread dissemination of plasmid-mediated colistin resistance gene mcr-1 in the E. coli incurs potential threat to public health. Here, we investigated the epidemiology, transmission dynamics, and genetic characterization of mcr-1 harboring E. coli isolates from poultry origin in Hebei province, China.

METHODS

A total of 297 fecal samples were collected from the two large poultry farms in Hebei province, China. The samples were processed for E. coli identification by MALDI-TOF-MS and 16S rD4A sequencing. Then, mcr-1 gene harboring E. coli strains were identified by PCR and subjected to antimicrobial susceptibility testing by broth microdilution assay. The genomic characterization of the isolates was done by whole genome sequencing using the various bioinformatics tools, and multi-locus sequence typing (MLST) was done by sequence analysis of the seven housekeeping genes. The conjugation experiment was done to check the transferability of mcr-1 along with the plasmid stability testing.

RESULTS

A total of six mcr-1 E. coli isolates with MIC of 4 μg/mL were identified from 297 samples (2.02%). The mcr-1 harboring E. coli were identified as MDR and belonged to ST101 (n=4) and ST410 (n=2). The genetic environment of mcr-1 presented its position on IncHI2 plasmid in four isolates and p0111 in two isolates which is rarely reported plasmid type for mcr-1. Moreover, both type of plasmids was transferable to recipient J53, and mcr-1 was flanked by three mobile elements ISApl1, Tn3, and IS26 forming a novel backbone Tn3-IS26-mcr-1- pap2-ISApl1 on p0111 plasmid. The phylogenetic analysis shared a common lineage with mcr-1 harboring isolates from the environment, human and animals which indicate its horizontal spread among the diverse sources, species, and hosts.

CONCLUSION

This study recommends the one health approach for future surveillance across multiple sources and bacterial species to adopt relevant measures and reduce global resistance crises.

Epidemiological, Genetic, and Phenotypic Characteristics of Non-Typhoidal Salmonella in Young Children, as Obtained from a Tertiary Hospital in Guangzhou, China

Gastroenteritis caused by non-typhoidal Salmonella (NTS) is a significant disease in childhood, ranking as the seventh-leading cause of diarrhea mortality in children aged < 5 years. To understand the epidemiological, genetic, and phenotypic characteristics of NTS, 465 anal swabs from children aged < 5 years in a tertiary hospital in Conghua District, Guangzhou, China, were collected from June to October 2021. An average prevalence of 35.27% (164/465) was observed, with whole genome sequencing identifying 11 serotypes, among which Salmonella 1,4,[5],12:i:- was the most prevalent (65.24%, 107/164). Meanwhile, ST34 was found to be the predominant subtype. Children who are breastfed, eat fresh food, and have good hygiene habits show a relatively low prevalence of NTS. Fever is a common symptom that may be caused by NTS infection. Antimicrobial resistance testing revealed that the majority of strains were resistant to tetracycline (83.5%) and ampicillin (82.3%), with multi-drug resistance (MDR) observed in 50.61% (83/164) of all strains tested. The predominant resistance spectrum presents as tetracycline-ampicillin-chloramphenicol-trimethoprim-sulfamethoxazole (30.49%, 50/164). The antimicrobial resistance rates (2.4%, 9.8%, 9.8%, 10.4%, 9.1%, and 3.7%, respectively) of cephalosporins (cefepime, cefuroxime, cefuroxime axetil, ceftriaxone, ceftazidime, and cefoxitin) were low. Therefore, continued surveillance of the prevalence and MDR profiles of NTS, along with the rational use antibiotics, is required. This protocol is significant for preventing further dissemination of NTS and formulating effective prevention and control strategies.

The Occurrence and Genomic Characteristics of mcr-1-Harboring Salmonella from Retail Meats and Eggs in Qingdao, China

Salmonella are widely distributed foodborne pathogens and are often associated with food animal products. Colistin resistance mediated by mcr-1 is an increasing threat; however, data on the characteristics of mcr-1-harboring Salmonella among retail foods are still lacking. In this study, retail meats from 24 supermarkets and eggs from nine markets in Qingdao city were investigated to determine the presence and genomic characteristics of mcr-1-harboring Salmonella. We found the retail meats and eggs were highly contaminated by Salmonella, with detection rates of 17.5% (31/177) and 12.3% (16/130), respectively. A total of 76 Salmonella isolates were obtained in this study, and 77.6% showed multidrug resistance (MDR). The MDR proportion of egg isolates (97.5%) was significantly higher than that in meat isolates (55.6%) (p < 0.05). The most prevalent Salmonella serotypes were Typhimurium (56.6%) and Enteritidis (17.1%). Of the 76 Salmonella isolates, 40 possessed mcr-1. All 40 mcr-1-positive isolates were ST34 S. Typhimurium and were from eggs of eight brands. Different mcr-1-harboring isolates existed in the same egg, and some isolates from different egg samples or brands showed clonal relationships. The mcr-1 was located on similar IncHI2/HI2A MDR non-conjugative plasmids lacking transfer region, resulting in the failure of conjugation. The phylogenetic tree using genome sequences showed that the mcr-1-positive isolates from eggs clustered together with mcr-1-positive isolates from chicken and humans in China, revealing that mcr-1-positive egg-borne Salmonella might be derived from chicken and could potentially trigger outbreaks in humans. The high occurrence of mcr-1-harboring Salmonella in fresh eggs is alarming, and there is an urgent need to monitor mcr-1-harboring Salmonella in retail meats and eggs. We report for the first time the role of retail eggs in disseminating mcr-1-positive Salmonella and the risk of transmission of these MDR pathogens from retail food to humans should be evaluated comprehensively.

Antimicrobial resistance of Salmonella Indiana from retail chickens in China and emergence of an mcr-1-harboring isolate with concurrent resistance to ciprofloxacin, cefotaxime, and colistin

Salmonella enterica serotype Indiana (S. Indiana) in Chinese poultry meat has aroused widespread concern because of its high prevalence and strong antimicrobial resistance. In consideration of the relationship in our previous study between S. Indiana and co-resistance to ciprofloxacin and cefotaxime (CIP-CTX), which were the first-line drug which were used in Salmonella infection in clinical, the antimicrobial resistance (AMR) of 224 CIP-CTX co-resistant S. Indiana isolated from retail chicken samples in China were investigated, with the aim of characterizing the AMR profiles and related resistance mechanisms to ciprofloxacin and cefotaxime among these CIP-CTX co-resistant S. Indiana isolates, all of which showed multi-drug-resistant (MDR) phenotypes. GyrA (S83F and D87N/G) with ParC (T57S and S80R) were the dominant amino acid substitution types, with oqxA, oqxB, and aac (6′)-Ib-cr identified as common plasmid-mediated quinolone resistance (PMQR)-encoding genes. Five bla_CTX-M gene subtypes were identified with bla_CTX-M-65 ranking at the top. Equally important, we obtained one isolate CFSA664 harboring the mcr-1 gene was ESBL producer with co-resistance to nine in ten classes of tested drugs inclduing colistin. A single circular chromosome and 3 circular plasmids were found in its genome. Among the 26 AMR genes identified, 24 were located on plasmid pCFSA664-1, including three ESBL genes, while plasmid pCFSA664-3 owning only the mcr-1 gene and sharing the same backbone structure with plasmids from Enterobacteriaceae. No insertion sequences were found near the mcr-1 gene but a relaxase-encoding gene in the flank, which could transfer into E. coli J53 at a relatively high frequency. S. Indiana in this study exhibited highly drug-resistant phenotypes, contributing to the acceleration of the dissemination and emergence of this pathogen among different sources. Surveillance and a One Health strategy are needed to limit the emergence of S. Indiana along the food chain.