Susceptibility of Listeria monocytogenes to antimicrobial peptides.

We assessed the susceptibility of several pathogenic and non-pathogenic Listeria species to antimicrobial peptides of animal and plant origin. Human defensins and thionins were highly inhibitory, whereas protamine, snakin and magainin showed an intermediate effect. A temperature dependence in the activity of potato defensin was observed for Listeria monocytogenes and Listeria ivanovii. PrfA* L. monocytogenes mutants, that overexpress constitutively PrfA-dependent genes, were sensitive to the peptide independently of the temperature whereas isogenic PrfA(-) derivatives were constitutively resistant. These data indicate that the thermoregulated transcription factor PrfA controls the expression of bacterial products that influence the susceptibility or resistance to some antimicrobial peptides.