Effect of Residual Sanitizers on Salmonella enterica Biofilm Formation

Introduction: Salmonella enterica are a diverse group of bacteria that represent a serious risk to public health.  Bacterial attachment on food and contact surfaces can lead to biofilm formation, and once in this state, bacteria are more resistant to sanitization and may serve as a continuous contamination source.  Studies have shown that common sanitizers are not able to eradicate Salmonella enterica biofilms on food contact surfaces. Here we further explored this phenomenon by examining the effect of residual concentrations of common sanitizers on Salmonella biofilm formation on solid surfaces.            

Purpose:   To evaluate biofilm formation and sanitizer resistance of various Salmonella serotypes under different environmental conditions, and to investigate the effect of residual sanitizers on biofilm formation.  

Methods:   Sixty-four strains of four common Salmonella enterica serotypes isolated from cattle sources and from human cases of salmonellosis were tested for biofilm formation and sanitizer resistance under different environmental conditions using 96-well plate absorbance assays.  Biofilm formation also was assessed after the addition of trace amounts of sanitizers to both planktonic cultures and pre-existing biofilms.  

Results: Biofilm formation by various Salmonella serotypes was dependent upon specific cell surface structures and environmental conditions.  Survival and recovery of biofilm cells after sanitization correlated with high biofilm mass that provided better protection. The presence of trace amounts of sanitizers enhanced biofilm formation of planktonic Salmonella cultures as well as increased bacterial colonization (P < 0.05) on pre-existing biofilms (P < 0.05). This was observed in certain Salmonella strains but not in all strains tested. These data suggest the existence of a unique genetic control mechanism responsible for this observation, which requires further investigation. 

Significance:  The observation that residual sanitizers could increase Salmonella biofilm formation highlights the importance of establishing proper sanitization and cleaning procedures in commercial meat plants.