Enhanced inactivation of Salmonella enterica Enteritidis biofilms on the stainless steel surface by proteinase K in the combination with chlorine

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/cm 2 , 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. • Cellulase, DNase I, or proteinase K can reduce Salmonella Enteritidis biofilms. • Proteinase K with chlorine synergistically inactivated S. Enteritidis biofilm. • The combined treatment was less effective against biofilm formed in diluted medium. • Biofilm morphology was changed by the combined treatment. • Proteinase K could promote chlorine penetration in biofilm.