Investigating how Salmonella colonise alfalfa using a whole genome screen

Enteropathogenic bacteria including Salmonella regularly cause outbreaks of infection from fresh produce posing a significant public health threat. Salmonella ’s ability to persist on fresh produce for extended periods is partly attributed to its capacity to form biofilms, which poses a challenge to food decontamination and facilitates persistence in the food chain. Preventing biofilm formation on food products and in food processing environments is crucial for reducing the incidence of foodborne diseases. Understanding the mechanisms of colonisation and establishment on fresh produce will inform the development of decontamination approaches. We used Transposon-directed Insertion site sequencing (TraDIS- Xpress ) to investigate the mechanisms employed by Salmonella enterica serovar Typhimurium to colonise and establish itself on fresh produce at critical timepoints following infection. We established an alfalfa infection model and compared the findings to those obtained from glass surfaces. Our research revealed dynamic changes in the pathways associated with biofilm formation over time, with distinct plant-specific and glass-specific mechanisms for biofilm formation, alongside the identification of shared genes playing pivotal roles in both contexts. Notably, we observed variations in the significance of factors such as flagella biosynthesis, lipopolysaccharide (LPS) production, and stringent response regulation in biofilm development on plant versus glass surfaces. Understanding the genetic underpinnings of biofilm formation on both biotic and abiotic surfaces offers valuable insights that can inform the development of targeted antibacterial therapeutics, ultimately enhancing food safety throughout the food processing chain. Funding The authors gratefully acknowledge the support of the Biotechnology and Biological Sciences Research Council (BBSRC); ERH, JAA, HAK, MAW and ET were supported by the BBSRC Institute Strategic Programme Microbes and Food Safety BB/X011011/1 and its constituent project BBS/E/F/000PR13635. NV was supported by the Food Safety Research Network grant BB/X002985/1 awarded to ET. Data availability Nucleotide sequence data supporting the analysis in this study has been deposited in ArrayExpress under the accession number E-MTAB-13495. The authors confirm all supporting data, code and protocols have been provided within the article or through supplementary data files. ### Competing Interest Statement The authors have declared no competing interest.