Resistance of Escherichia coli and Salmonella against nisin and curvacin A

We have determined the effects of the following factors on the resistance o f Gram-negative bacteria against nisin and curvacin A: (i) chemotype of the lipopolysaccharide (LPS), (ii) addition of agents permeabilizing the outer membrane, (iii) the fatty acid supply of the growth medium, and (iv) the a daptation to acid and salt stress. Bacteriocin activity was determined agai nst growing and resting cells as well as protoplasts. All smooth strains of Escherichia coli and Salmonella enterica serovar Typhimurium were highly r esistant towards the bacteriocins, whereas mutants that possess the core of the LPS, but not the O antigen, as well as deep rough LPS mutants were sen sitive. Antibiotics with outer membrane permeabilizing activity, polymyxin B and polymyxin B nonapeptide, increased the sensitivity of smooth E. coli towards nisin, but not that of deep rough mutants. Incorporation of 1 g l(- 1) of either oleic acid or linoleic acid to the growth media greatly increa sed the susceptibility of E. coli LTH1600 and LTH4346 towards bacteriocins. Both strains of E. coli were sensitive to nisin and curvacin A at a pH of less than 5.5 and more than 3% (w/v) NaCl. Adaptation to sublethal pH or hi gher NaCl concentrations (pH 4.54 and 5.35 or 4.5% (w/v) NaCl) provided onl y limited protection against the bacteriocidal activity of nisin and curvac in A. Adaptation to 4.5% (w/v) NaCl did not result in cross protection to b acteriocin activity at pH 4.4, but rendered the cells more sensitive toward s bacteriocins. (C) 1999 Elsevier Science B.V. All rights reserved.