Polycations sensitize enteric bacteria to antibiotics

Abstract

Polymyxin B nonapeptide, a polymyxin B derivative which lacks the fatty acyl part and the bactericidal activity of polymyxin, sensitized smooth encapsulated Escherichia coli (O18:K1) and smooth Salmonella typhimurium to hydrophobic antibiotics (novobiocin, fusidic acid, erythromycin, clindamycin, nafcillin and cloxacillin). The polymyxin B nonapeptide-treated bacteria were as sensitive to these antibiotics as deep rough mutants. A lysine polymer with 20 lysine residues (lysine20) had a largely similar effect. Larger lysine polymers and the protamine salmine were bactericidal but, at sublethal concentrations, sensitized the strains to the antibiotics mentioned above; lysine4, streptomycin, cytochrome c, lysozyme and the polyamines cadaverine, spermidine and spermine had neither bactericidal nor sensitizing activity.