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Background <p><i>Salmonella</i> is the primary enteric pathogen related to foodborne illnesses worldwide, posing significant public health concerns. Amongst the diversity and pathogenicity of over 2000 <i>Salmonella</i> serovars, <i>Salmonella</i> Infantis (<i>S.</i> Infantis) ranks among the top <i>Salmonella</i> serovars implicated in foodborne outbreaks, with thousands of reported cases annually in the United States. Moreover, the incidence of <i>S.</i> Infantis infections has spread rapidly worldwide from the U.S. to Europe, where more than 50% of isolated <i>S.</i> Infantis strains have developed antibiotic resistance. Previous studies have demonstrated that antibiotic resistance genes (ARGs), particularly those carried by plasmids, contribute to the persistence and spread of multipledrug-resistant (MDR) <i>Salmonella</i> strains in various environments. However, the information regarding the multidrug resistance and spread of <i>S.</i> Infantis is scarce. Hence, the objectives of this study were to characterize antibiotic-resistant <i>S.</i> Infantis isolated from the poultry production line in the United States and to examine the correlation between mobile genetic elements and bacterial resistome evolution.</p> Results <p>A total of 9 <i>S.</i> Infantis strains were isolated from poultry production lines in 2022, including comminuted chicken, raw intact/nonintact chicken, and chicken carcass. These strains were further subject to antimicrobial susceptibility tests, whole-genome sequencing, and bioinformatic analysis. Most strains were MDR and phenotypically resistant to five or more antibiotics, such as Streptomycin and Tetracycline. The complete bacterial genome results showed that all isolates had a dsDNA chromosome with a GC content of 52.3% and an average genome size of 4,730&#xa0;kb, belonging to the sequence type 32. The genomic characterization of <i>S.</i> Infantis isolates revealed that each strain contained one IncFIB mega-plasmid with lengths from 289 to 327&#xa0;kb. Five or more ARGs were detected in each strain, most of which were located in the mega-plasmids and bordered by diverse mobile genetic elements, including transposons, integrons, and prophages. The common ARGs present in the mega-plasmids included <i>bla</i><sub>CTX−M−65</sub>, <i>aac(3)-IV</i>, <i>tetA</i>, <i>suil1</i>, <i>dfrA14</i>, <i>ant(3’’)-Ia</i> and <i>floR.</i> Moreover, the majority of whole-genome sequencing (WGS)-derived ARG profiles had concordant phenotypic traits.</p> Conclusion <p>These findings reveal the genomic features and antimicrobial resistance profiles of <i>S.</i> Infantis strains from poultry production lines in the United States, indicating the potential of mobile genetic elements-driven <i>S.</i> Infantis resistome development.</p>

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Mobile genetic elements drive the evolution and multidrug resistance of Salmonella infantis along the United States poultry production line

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年3月3日

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  • Yujie Zhang,
  • Mackenna Chu,
  • Sanghvi Samala,
  • Alexandra Salvador,
  • Yen-Te Liao,
  • Vivian C.H. Wu

摘要

Background

Salmonella is the primary enteric pathogen related to foodborne illnesses worldwide, posing significant public health concerns. Amongst the diversity and pathogenicity of over 2000 Salmonella serovars, Salmonella Infantis (S. Infantis) ranks among the top Salmonella serovars implicated in foodborne outbreaks, with thousands of reported cases annually in the United States. Moreover, the incidence of S. Infantis infections has spread rapidly worldwide from the U.S. to Europe, where more than 50% of isolated S. Infantis strains have developed antibiotic resistance. Previous studies have demonstrated that antibiotic resistance genes (ARGs), particularly those carried by plasmids, contribute to the persistence and spread of multipledrug-resistant (MDR) Salmonella strains in various environments. However, the information regarding the multidrug resistance and spread of S. Infantis is scarce. Hence, the objectives of this study were to characterize antibiotic-resistant S. Infantis isolated from the poultry production line in the United States and to examine the correlation between mobile genetic elements and bacterial resistome evolution.

Results

A total of 9 S. Infantis strains were isolated from poultry production lines in 2022, including comminuted chicken, raw intact/nonintact chicken, and chicken carcass. These strains were further subject to antimicrobial susceptibility tests, whole-genome sequencing, and bioinformatic analysis. Most strains were MDR and phenotypically resistant to five or more antibiotics, such as Streptomycin and Tetracycline. The complete bacterial genome results showed that all isolates had a dsDNA chromosome with a GC content of 52.3% and an average genome size of 4,730 kb, belonging to the sequence type 32. The genomic characterization of S. Infantis isolates revealed that each strain contained one IncFIB mega-plasmid with lengths from 289 to 327 kb. Five or more ARGs were detected in each strain, most of which were located in the mega-plasmids and bordered by diverse mobile genetic elements, including transposons, integrons, and prophages. The common ARGs present in the mega-plasmids included blaCTX−M−65, aac(3)-IV, tetA, suil1, dfrA14, ant(3’’)-Ia and floR. Moreover, the majority of whole-genome sequencing (WGS)-derived ARG profiles had concordant phenotypic traits.

Conclusion

These findings reveal the genomic features and antimicrobial resistance profiles of S. Infantis strains from poultry production lines in the United States, indicating the potential of mobile genetic elements-driven S. Infantis resistome development.