Investigating the effect of alkaline stress on biofilm formation by Salmonella enteritidis

Bacterial biofilm formation is an important survival strategy in multiple environments. It is affected by the attachment surface, the bacterial strain and the surrounding environment. In Salmonella enteritidis, a biofilm-forming foodborne pathogen, the molecular biofilm regulators act as on-off controls between the sessile and the planktonic population, while the exact underlying formation mechanism still remains unclear. The aim of this project is to study the effect of alkaline environment on the formation of Salmonella biofilms and to examine the architecture of biofilm produced under alkaline conditions, by use confocal microscopy. Neutral pH was found to be the optimal pH for Salmonella biofilm formation, while pH 10 significantly reduces it (P-value=0.015). However, cell viability remains high at pH 10, which suggests that the pathogen can easily survive the alkaline stress. Biofilm morphology at pH 7 is characterized by thick cell clusters, whereas at pH 10 it is characterised by thin layers of individual cells. These findings can help us understand how Salmonella enteritidis survives under highly alkaline conditions, potentially leading to the design of new and more effective disinfection strategies involving highly alkaline detergents.