Effects of cellulase, proteinase K, chlorine, and their combination on Salmonella enterica Gaminara biofilms on food contact surfaces at nutrient availability

This study aimed to investigate the effects of cellulase, proteinase K, chlorine, and their combination on Salmonella Gaminara biofilms on food contact surfaces at nutrient availability and to elucidate the mechanisms by determining cellulose production, membrane permeability, and morphological change. Results showed that cellulase and proteinase K significantly reduced biofilm cells formed in tryptic soy broth (TSB) on polystyrene and stainless steel surfaces by 0.7–1.5 log CFU/cm 2 ( P < 0.05), but not on glass. In 20-fold diluted TSB (1/20 TSB), only proteinase K was effective on stainless steel, with reduction of 1.2 log CFU/cm 2 . While chlorine treatment resulted in the limited reduction (<1 log CFU/cm 2 ) for biofilms in TSB, it resulted in the reduction of 3.8–4.2 log CFU/cm 2 for biofilms in 1/20 TSB. For the combination, cellulase or proteinase K followed by chlorine significantly inactivated biofilm cells formed in 1/20 TSB by 5.2–6.6 log CFU/cm 2 and in TSB by 3.2–4.7 log CFU/cm 2 ( P < 0.05), revealing the synergistic effect on both surfaces. Microscopic observations revealed that the combined treatment resulted in greater changes in biofilm morphology, particularly in the cytoplasmic membranes. In addition, no cell appendages such as curli fimbriae and pili were found in proteinase K-treated biofilm. Moreover, no increase in resistance was observed after repeated treatment of proteinase K followed by chlorine for four consecutive days. Therefore, these findings suggest that bio-enzyme may help chlorine to easily penetrate the biofilm matrix, which means bio-enzyme with chlorine-based disinfectants has the potential to control Salmonella biofilms.