Life sciences · Journal article

Phenotypic and genomic characteristics of Salmonella isolates from 99,780 wet market workers in Shanghai

BMC Microbiology · August 11, 2026

Preliminary Why this matters to you Expert discussion

Early or partial results. Treat as a signal, not a conclusion.

AI Summary

This is a large cross-sectional surveillance study documenting Salmonella carriage and antimicrobial resistance patterns in 99,780 asymptomatic wet market workers in Shanghai. The study identified a Salmonella prevalence of 0.12% with notable resistance to third-generation cephalosporins (17.24%) and fluoroquinolones (11.21%), and is the first to detect tet(X4)-harboring Salmonella in asymptomatic carriers in this setting. The findings provide baseline epidemiological data for understanding community transmission of resistant S. enterica but do not establish causality, compare populations, or evaluate interventions.

What was studied

Cross-sectional surveillance study with whole-genome sequencing and phenotypic analysis. Asymptomatic wet market workers in Shanghai, China; sampling across six districts in 2023.. n = 99,780. Six districts in Shanghai, China.

Key findings

Salmonella prevalence of 0.12% (116 isolates from 99,780 wet market workers) in Shanghai in 2023 Resistance to third-generation cephalosporins in 17.24% of isolates and fluoroquinolones in 11.21% qnrS1 gene prevalence 31.03%, bla CTX-M-55 5.17%, mph(A) 12.93%, fosA7 12.07% of isolates

Safety

Safety was not reported in the material analysed. Check the source before drawing any conclusion about harm.

Who this may help

This surveillance study documents the burden and resistance patterns of Salmonella in an occupationally exposed asymptomatic population, highlighting a potential reservoir for community transmission of resistant strains. The data may inform public health surveillance and infection control strategies for food-handling environments but does not directly address clinical diagnosis, treatment, or prevention in symptomatic patients.

Plain-language summary

A large cross-sectional surveillance study in asymptomatic carriers with genomic characterization, but descriptive in design with no comparator group, control arm, or hypothesis test; provides epidemiological baseline data rather than evaluating an intervention or clinical outcome.

Study design

As stated by the source record.

MethodsSalmonella isolates obtained from 99,780 wet market workers across six districts in Shanghai during 2023. Isolates underwent phenotypic antimicrobial susceptibility testing and whole-genome sequencing. Phylogenetic analysis was performed on predominant serovars. Resistance genes were identified and characterized at the genomic level.

DesignCross-sectional surveillance study with whole-genome sequencing and phenotypic analysis

PopulationAsymptomatic wet market workers in Shanghai, China; sampling across six districts in 2023.

Sample size99,780

SettingSix districts in Shanghai, China

Reported figures

Quoted from the source exactly as published.

Salmonella prevalence0.12%

Sample size99780

Number of isolates116

Resistance to third-generation cephalosporins17.24%

Resistance to fluoroquinolones11.21%

qnrS1 prevalence31.03%

bla CTX-M-55 prevalence5.17%

mph(A) prevalence12.93%

Clinical bottom line

Caveats

Descriptive cross-sectional study with no comparison group or control; cannot establish causation or risk factors
No confidence intervals or statistical inference reported; prevalence estimates lack precision measures
Selection bias possible if enrollment of workers was not systematic across all market types and districts
No follow-up data; cannot assess persistence of carriage, transmission routes, or clinical outcomes in exposed contacts

Evidence assessment

Graded across the dimensions that decide whether you should act, each from what the source actually supports. There is no single score, and where a dimension was not assessed it says so.

Study design

moderate

Large cross-sectional survey with whole-genome sequencing and phenotypic testing; no control or comparator group.

Directness

strong

Directly measures Salmonella prevalence and AMR patterns in the target population of wet market workers.

Consistency

insufficient

Source does not compare findings to prior studies or discuss consistency with other datasets.

Risk of bias

moderate

Surveillance study; potential selection bias if workers were not systematically enrolled; no blinding discussed.

Sample adequacy

strong

Large sample of 99,780 workers; 116 Salmonella isolates provide adequate numbers for prevalence and resistance profiling.

Source abstract

Antimicrobial resistance (AMR) in Salmonella enterica ( S. enterica ) poses an increasing public health threat. To better understand and assess the prevalence and AMR patterns of Salmonella carried by asymptomatic individuals, whole-genome sequencing and phenotypic analysis were used to investigate the epidemiology and AMR patterns within Salmonella isolates from 99,780 wet market workers in Shanghai, China. A total of 116 Salmonella isolates (0.12%) were isolated from 99,780 wet market workers in 2023 across six districts in Shanghai, China. The predominant serovars were S. I 1,4,[5],12:i:- and S. London. Antimicrobial phenotypic tests showed that 17.24% and 11.21% of these isolates were resistant to third-generation cephalosporins and fluoroquinolones, respectively, with marked serovar disparity. The prevalence of qnrS1, bla CTX-M-55, mph(A), and fosA7 was 31.03%, 5.17%, 12.93%, and 12.07% of these isolates, respectively. Phylogenetic analysis indicated that S. I 1,4,[5],12:i:- ST34 strains diversified into five distinct clades, each harboring a unique resistance gene array. Two isolates carried the tigecycline resistance gene tet (X4) that were highly homologous to plasmids from both human and porcine Salmonella in China, with tet (X4) flanked by IS CR2 and IS 1 -family elements. To our knowledge, this is the first study to uncover the prevalence (0.12%) of Salmonella among 99,780 wet market workers, and the first detection of tet (X4)-harboring Salmonella in asymptomatic carriers in Shanghai. These findings underscore the critical role of asymptomatic carriers in the community spread of resistant S. enterica and provide crucial baseline data for future genomic surveillance and control strategies.

Follow from this

Taken from the source record, never inferred. Follow any of these and new work involving them reaches your briefing.

Yanan WangSujuan YangYibin ZhouZiru YangYuhang PeiYue Liu