LAUSR

Abstract This study aimed to determine the enzymatic effect of cellulase, DNase I, and proteinase K on Salmonella enterica Enteritidis biofilms on the stainless steel surface at nutrient availability [tryptic soy broth (TSB) and 20 times diluted TSB (1/20 TSB)] and to evaluate the synergistic effect of proteinase K combined with chlorine (50 ppm for 1 min). The results showed that cellulase and proteinase K degraded S. Enteritidis ME 14 biofilms, regardless of nutrient availability, whereas S. Enteritidis ATCC 13076 biofilms formed in TSB were effectively degraded by all the enzymes tested, but resistant to cellulase and DNase I in 1/20 TSB. Proteinase K or chlorine alone reduced the two S. Enteritidis biofilms formed in TSB by 1.1–1.5 log CFU/cm2, while the combined treatment with proteinase K followed by chlorine resulted in 3.8–6.1 log reductions, revealing the synergistic effect. On the contrary, both S. Enteritidis biofilms formed in 1/20 TSB were more resistant to proteinase K treatment followed by chlorine than TSB. Furthermore, microscopic observation using Live/Dead® assay and scanning electron microscopy (SEM) showed that biofilm morphology was greatly altered by the combined treatment, and proteinase K might make it easier for chlorine to penetrate the biofilm matrix. Therefore, these results indicate proteinase K with chlorine-based sanitizer has a potential for effective control of Salmonella biofilms formed on the food contact surface, decreasing the chance of cross-contamination and the risk of salmonellosis.