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

Clonal spread of blaNDM-1-carrying Salmonella enterica serovar Typhimurium clone ST34 and wide spread of IncHI2/ST3-blaNDM-5 plasmid in China

OBJECTIVES

To characterize blaNDM-carrying Salmonella recovered from a pig slaughterhouse.

METHODS

In this study, 46 environment samples were collected from a slaughterhouse in China, and screened for carbapenem-resistant Enterobacterales. WGS, antimicrobial susceptibility testing and conjugation experiments were carried out to identify the isolates' resistance phenotypes and genetic characteristics. The phylogenetic relatedness of the Salmonella isolates obtained in this study and Salmonella (ST34 and ST29) in GenBank was determined.

RESULTS

Two ST34 Salmonella Typhimurium and one ST29 Salmonella Stanley, recovered from three environmental samples (6.52%), were positive for blaNDM-1 and blaNDM-5, respectively. The two ST34 S. Typhimurium strains exhibited a close relationship (10-36 SNPs) with two human-derived blaNDM-1-bearing isolates from China (Hong Kong and Guangxi Province) and two blaNDM-negative ST34 Salmonella strains from the UK. The blaNDM-1 genes were located on IncHI2/ST3 plasmids. The capture of blaNDM-1 by the IncHI2/ST3 plasmid seems to be due to homologous recombination mediated by circular structures, as the genetic arrangements of the blaNDM-1 gene contain two IS26 elements of the same orientation. The blaNDM-5 gene was also carried by the IncHI2/ST3 plasmid, which shares highly similar structures with other blaNDM-5-bearing IncHI2/ST3 plasmids from other sources (fish, chicken, duck, human).

CONCLUSIONS

This is the first report of a blaNDM-5-carrying IncHI2/ST3 plasmid in Salmonella. The clonal spread of NDM-1-producing ST34 S. Typhimurium across human and animal-associated environments, and the widespread dissemination of epidemic blaNDM-5-carrying IncHI2/ST3 plasmids among Enterobacteriaceae in China indicate the potential of further dissemination of blaNDM among Salmonella, which poses a threat to public health.

Genomic characterization of Salmonella isolated from retail chicken and humans with diarrhea in Qingdao, China

Salmonella, especially antimicrobial resistant strains, remains one of the leading causes of foodborne bacterial disease. Retail chicken is a major source of human salmonellosis. Here, we investigated the prevalence, antimicrobial resistance (AMR), and genomic characteristics of Salmonella in 88 out of 360 (24.4%) chilled chicken carcasses, together with 86 Salmonella from humans with diarrhea in Qingdao, China in 2020. The most common serotypes were Enteritidis and Typhimurium (including the serotype I 4,[5],12:i:-) among Salmonella from both chicken and humans. The sequence types were consistent with serotypes, with ST11, ST34 and ST19 the most dominantly identified. Resistance to nalidixic acid, ampicillin, tetracycline and chloramphenicol were the top four detected in Salmonella from both chicken and human sources. High multi-drug resistance (MDR) and resistance to third-generation cephalosporins resistance were found in Salmonella from chicken (53.4%) and humans (75.6%). In total, 149 of 174 (85.6%) Salmonella isolates could be categorized into 60 known SNP clusters, with 8 SNP clusters detected in both sources. Furthermore, high prevalence of plasmid replicons and prophages were observed among the studied isolates. A total of 79 antimicrobial resistant genes (ARGs) were found, with aac(6')-Iaa, blaTEM-1B, tet(A), aph(6)-Id, aph(3″)-Ib, sul2, floR and qnrS1 being the dominant ARGs. Moreover, nine CTX-M-type ESBL genes and the genes blaNMD-1, mcr-1.1, and mcr-9.1 were detected. The high incidence of MDR Salmonella, especially possessing lots of mobile genetic elements (MGEs) in this study posed a severe risk to food safety and public health, highlighting the importance of improving food hygiene measures to reduce the contamination and transmission of this bacterium. Overall, it is essential to continue monitoring the Salmonella serotypes, implement the necessary prevention and strategic control plans, and conduct an epidemiological surveillance system based on whole-genome sequencing.

Genomic analysis of almost 8,000 Salmonella genomes reveals drivers and landscape of antimicrobial resistance in China

IMPORTANCE

We established the largest Salmonella genome database from China and presented the landscape and spatiotemporal dynamics of antimicrobial resistance genes. We also found that economic, climatic, and social factors can drive the rise of antimicrobial resistance. The Chinese local Salmonella genome database version 2 was released as an open-access database (https://nmdc.cn/clsgdbv2) and thus can assist surveillance studies across the globe. This database will help inform interventions for AMR, food safety, and public health.

Microevolution of Salmonella 4,[5],12:i:- derived from Salmonella enterica serovar Typhimurium through complicated transpositions

Salmonella enterica subsp. enterica serovar 4,[5],12:i:- (Salmonella 4,[5],12:i:-), derived from S. Typhimurium, has become the dominant serotype causing human salmonellosis. In this study, we define the genetic mechanism of the generation of Salmonella 4,[5],12:i:- from S. Typhimurium through complicated transpositions and demonstrate that Salmonella 4,[5],12:i:- displays more efficient colonization and survival abilities in mice than its parent S. Typhimurium strain. We identified intermediate strains carrying both resistance regions (RRs) and the fljAB operon for the generation of Salmonella 4,[5],12:i:-. The insertion of RR3 into the chromosomal hin-iroB site of S. Typhimurium produced RR3-S. Typhimurium as a primary intermediate. Salmonella 4,[5],12:i:- was then produced by replacing the fljAB operon and/or its flanking sequences through intramolecular transpositions mediated by IS26 and/or IS1R elements in RR3-S. Typhimurium, which was further confirmed both in vitro and in vivo. Overall, we demonstrate the molecular mechanism underlying the origin, generation, and advantage of RRs-Salmonella 4,[5],12:i:- from S. Typhimurium.

Non-Typhoidal Salmonella Infections Among Children in Fuzhou, Fujian, China: A 10-Year Retrospective Review from 2012 to 2021

Purpose

Non-typhoidal salmonella (NTS) infection is a leading cause of acute gastroenteritis in children. Recently, NTS infections have increased, especially those associated with Salmonella Typhimurium, which has become a global problem because of its high level of drug resistance. Diseases caused by NTS serotypes vary considerably. We summarised NTS infections among children in Fuzhou, Fujian, China, from 2012 to 2021, and synthesised studies indicating the clinical symptoms, laboratory test results, and drug resistance associated with S. Typhimurium and non-S. Typhimurium to enhance the knowledge of these infections and improve their diagnoses and treatment.

Patients and Methods

Between January 2012 and December 2021, 691 children with NTS infections confirmed by positive culture test results were recruited from Fujian Children's Hospital and Fujian Maternity and Child Health Hospital. Clinical demographic data of each case were collected from the electronic medical records and analysed.

Results

A total of 691 isolates were identified. The number of NTS infections increased significantly in 2017 and increased sharply during 2020 and 2021, especially S. Typhimurium greatly increased and was the dominant serotype (58.3%). S. Typhimurium infection was commonly occurred in children younger than 3 years and most of them were gastrointestinal infection, while non-S. Typhimurium more often observed in older children and associated with extra-intestinal infection. The rate of multidrug-resistant S. Typhimurium was significantly higher than that of non-S. Typhimurium, especially during the last 2 years of this study (2020 and 2021).

Conclusion

S. Typhimurium was the dominant serotype and greatly increased among children in Fuzhou city. There are significant differences in clinical symptoms, laboratory test results, and drug resistance between S. Typhimurium and non-S. Typhimurium. More attention should be paid on S. Typhimurium. Long-term high-quality surveillance and control measures should be conducted to prevent salmonella infections and drug resistance.