Abstract: Purpose: In order to control the contamination of Salmonella Derby during food processing, the inhibitory effect of different concentrations of sodium hypochlorite on the biofilm formation of Salmonella Derby was studied and the underlying mechanism was investigated. Methods: The crystal violet staining and plate counting methods were used to observe the potential of sodium hypochlorite to inhibit and eradicate Salmonella Derby biofilm, and the content of extracellular polymeric substances (EPS), biofilm metabolism, micromorphology and swimming mobility of Salmonella Derby in the presence of sodium hypochlorite at different concentrations were observed. Results: The minimum inhibitory concentration (MIC) of sodium hypochlorite was 0.08% (V/V), and the sub-MICs (0.04%, 0.02% and 0.01%) of sodium hypochlorite could inhibit the formation of Salmonella Derby biofilm, and also eradicate mature biofilms and the effect of sodium hypochlorite with different sub-MICs was significantly different (P < 0.05). Sodium hypochlorite could significantly reduce biofilm metabolism of Salmonella Derby and inhibit biofilm exopolysaccharide synthesis, and the effect of sodium hypochlorite with different concentrations was significantly different (P < 0.05). The results of confocal laser scanning microscopy (CLSM) showed that sodium hypochlorite treatment greatly reduced the thickness of the biofilm, reduced the number of live bacterial cells, increased the number of dead bacterial cells, and transform the biofilm cells from an aggregated state to a dispersed one. Conclusion: Sodium hypochlorite at different sub-MICs has a significant inhibitory effect on the formation of Salmonella Derby biofilms, possibly by interfering with bacterial growth, metabolism and extracellular polysaccharide secretion.

Key words: Salmonella Derby; biofilm; sodium hypochlorite; metabolism; extracellular polymeric substance