Dual-species biofilm and other profiles altered by interactions between Salmonella Typhimurium and Pseudomonas fluorescens isolated from meat.

Salmonella Typhimurium is a significant foodborne pathogen that poses substantial health risks to humans. Pseudomonas fluorescens is a key bacterium responsible for meat deterioration through the production of spoilage-associated enzymes. Both species are widely presented in meat, and can form dense biofilms on slaughterhouse equipment surfaces, acting as persistent sources of bacterial contamination that compromise both safety and quality issues in the meat industry. However, how ecological interactions between S. Typhimurium and P. fluorescens affect the function and stability of mixed-species biofilms remain largely unexplored. The purpose of this work is to investigate the altered profiles of a mixed-species biofilm by meat-derived S. Typhimurium N25 and P. fluorescens PF2 through RNA-sequencing analysis in combined with phenotype validation, including the bacterial growth and antibiotic resistance of planktonic cells, biofilm-forming capacity, biofilm structures, and biofilm EPS production. The results demonstrated that the presence of S. Typhimurium inhibited the growth of P. fluorescens PF2 in its planktonic state, and reduced the biofilm cell count of P. fluorescens PF2 in mixed-species biofilm when compared to that in mono-species biofilm. Furthermore, the bacterial interaction led to decreased protein and carbohydrate contents in the biofilm matrix, and reductions in biofilm coverage, average thickness, and total biomass. RNA-sequencing analysis revealed that 580 differentially expressed genes (DEGs) were mainly involved in eight downregulated pathways related to carbohydrate, amino acid, and organic acid salt metabolism. Additionally, 62 DEGs in S. Typhimurium N25 were significantly enriched in five upregulated pathways (bacterial chemotaxis, bacterial invasion of epithelial cells, Salmonella infection, two-component system, and flagellar assembly). The results facilitate updated knowledge of the complex dynamics governing biofilms formation by S. Typhimurium and P. fluorescens, which provide a theoretical foundation for improved control strategies to ensure meat safety in the food industry.