Competitive exclusion of uropathogenic E. coli biofilm by Salmonella through matrix inhibition

Biofilm is a predominant lifestyle of bacteria in host and non-host environments with cell collectives and extracellular matrix as the defining principles of biofilm. Several factors trigger biofilm formation including response to competition. Urinary tract infections (UTI) are highly prevalent worldwide and mainly caused by uropathogenic E. coli (UPEC), which progresses into chronic form due to the biofilm formation by the pathogen. In this study, we hypothesized that competition for territorial space could occur between species by intervening in the biofilm matrix production, particularly of UPEC, thereby reducing its colonizing ability. UPEC colony displays different morphology in congo red media based on matrix production, which we exploited for screening bacterial isolates capable of inhibiting the matrix. This was validated by using the cell-free supernatants of the isolates to impair UPEC biofilm. Isolates that inhibited matrix production belonged to species of Shigella, Escherichia, Enterobacter, and Salmonella from Enterobacteriaceae family. Competition experiments between the isolates and UPEC revealed spiteful interactions particularly during biofilm formation, indicating fierce competition for territorial space colonization. The isolate Salmonella enterica B1 could competitively exclude UPEC in the biofilm. Altogether, we show that interference competition by matrix inhibition occurs as a strategy by bacteria to colonize territorial space.