Mapping Salmonella’s Pathogenic Potential

Simran Krishnakant Kushwaha, PhD

(Credit: LinkedIn)

Understanding the dynamic evolution of Salmonella is crucial for managing bacterial infections effectively. This study investigates how the flexible genome of Salmonella, organized into regions of genomic plasticity (RGP), influences the pathogenicity of various Salmonella lineages. By mapping genomic spots in nonpathogenic lineages that could harbor pathogenicity genes, the study provides a blueprint for Salmonella’s pathogenicity potential.¹

The research, conducted by Simran Krishnakant Kushwaha, PhD, a Computational Biologist at the University of Liverpool, and colleagues, uncovered distinct patterns of integration for pathogenicity-related gene clusters within RGP, challenging traditional views on gene distribution in Salmonella. RGP exhibit specific preferences for certain genomic locations, and the presence or absence of these integration spots significantly impacts strain pathogenicity.¹

“Surprisingly, our findings revealed a distinctive pattern of nonrandom integration of gene clusters into specific RGP in Salmonella,” Kushwaha and coinvestigators wrote. “This pattern challenges established notions of gene distribution and demonstrates how RGP can reshape our understanding of gene presence and absence across different lineages.”¹ This insight opens new avenues for research into the mechanisms driving gene integration and regulation.

These preferences are influenced by conserved flanking genes, which may play a role in regulatory networks and interact functionally with the integrated gene clusters. Additionally, the study highlights the significant contributions of plasmids and prophages to the pathogenicity of various Salmonella lineages.¹

“Unsurprisingly, we observed that chromosomal mutations and plasmids prominently influence antibiotic resistance (ABR) patterns within Salmonella. Specifically, a substantial proportion (84%) of ABR determinants were located on the chromosome, while 16% were found within plasmids, with notable variations across subspecies and serovars,” investigators wrote.¹ This reinforces the current understanding of how antibiotic resistance develops and persists in bacterial populations.

The study involved an extensive genomic analysis of 12,244 Salmonella spp. genomes, including 2 species, 6 subspecies, and 46 serovars. The analysis aimed to identify the integration patterns of pathogenicity-related gene clusters within RGP and to explore the role of plasmids and prophages in influencing pathogenicity.¹

What to Know About Salmonella Infection

The CDC estimates that Salmonella bacteria lead to around 1.35 million infections, 26,500 hospitalizations, and 420 deaths in the United States each year, with most cases originating from contaminated food.²

Common symptoms include diarrhea, fever, and stomach cramps, typically appearing 6 hours to 6 days after infection and lasting 4 to 7 days. Most people recover on their own, and antibiotics are usually only prescribed for severe cases or those at high risk. Severe infections may require hospitalization.²

Most Current Salmonella Issues in the US

Following an October 2023 voluntary recall of raw milk from Raw Farm due to about a dozen Salmonella cases in California, further investigation revealed that over 60% of those interviewed had consumed Raw Farm products. Nearly 40% of the cases were in children under five. Twenty people were hospitalized, with no reported deaths.³

Overall, the insights from this study help predict future Salmonella adaptations and support the development of targeted strategies to combat emerging pathogenic strains.

References

1. Kushwaha S, Wu Y, Avila H, et. Al. Comprehensive blueprint of Salmonella genomic plasticity identifies hotspots for pathogenicity genes. PLOSBIOLOGY. Published August 7, 2024. Accessed August 8, 2024. Doi: https://doi.org/10.1371/journal.pbio.3002746

2. CDC. Salmonella. Last reviewed June 18, 2024. Accessed August 8, 2024. https://www.cdc.gov/salmonella/index.html

3. Aleccia J. Dozens were sickened with salmonella after drinking raw milk from a California farm. https://apnews.com/article/raw-milk-salmonella-bird-flu-raw-farm-99c8c79ece9bc2a9f90dc4f917292dad?utm_campaign=TrueAnthem&utm_medium=AP&utm_source=Twitter