Inhibition of planktonic and sessile Salmonella enterica cells by combinations of enterocin AS-48, polymyxin B and biocides

Enterocin AS-48 was tested against planktonic Salmonella enterica UJ3197 in combination with polymyxin B and/or biocides. Enterocin AS-48 added at 50 mg/l or 100 mg/l in combination with 2 mg/l polymyxin B caused partial or complete growth inhibition of S. enterica UJ3197 at 24 h incubation. At 2 mg/l, polymyxin B did not enhance significantly the inhibitory effect of biocides against strain UJ3197, except for 25 mg/l cetrimide. The combination of polymyxin B (2 mg/l) and enterocin AS-48 (25 mg/l) significantly inhibited growth of strain UJ3197 in combination with 2.5 or 25 mg/l cetrimide, 25 mg/l hexadecylpyridinium chloride, 500 mg/l chlorhexidine, and also with 0.16 or 1.6 mg/l poly-(hexamethylen guanidinium) hydrochloride. Biofilms formed by four Salmonella strains (S62, S64, UJ3197, UJ3198) on polystyrene microtiter plates were treated with biocides singly or in combinations with polymyxin B (2 mg/l), enterocin AS-48 (25 or 50 mg/l) or both. Sessile salmonellae showed an increased tolerance to all biocides tested compared to planktonic cells. At the concentration tested, polymyxin B did not enhance the bactericidal activity for any of the biocides on sessile salmonellae. Enterocin AS-48 improved the activity of most biocides, but only for some of the strains and only for the highest bacteriocin concentration tested in most cases. The combinations of enterocin AS-48 and polymyxin B improved inactivation of sessile salmonellae for all biocides tested, although the degree of inactivation was highly dependent on strain and biocide. The combination of polymyxin B (2 mg/l) and enterocin AS-48 (50 mg/l) improved significantly (p < 0.05) the inactivation of all Salmonella strains in sessile state by the biocides benzalkonium chloride, cetrimide, triclosan, hexachlorophene, chlorhexidine, poly-(hexamethylen guanidinium) hydrochloride, and P3-oxonia.