A broad-spectrum bactericidal lipopeptide with anti-biofilm properties

Previous studies of the oligoacyllysyl (OAK) series acyl-lysyl-lysyl-aminoacyl-lysine-amide, suggested their utility towards generating robust linear lipopeptide-like alternatives to antibiotics, although to date, none exhibited potent broad-spectrum bactericidal activity. To follow up on this premise, we produced a new analog (C(14)KKc(12)K) and investigated its properties in various media. Mechanistic studies suggest that C(14)KKc(12)K uses a non-specific membrane-disruptive mode of action for rapidly reducing viability of Gram-negative bacteria (GNB) similarly to polymyxin B (PMB), a cyclic lipopeptide used as last resort antibiotic. Indeed, C(14)KKc(12)K displayed similar affinity for lipopolysaccharides and induced cell permeabilization associated with rapid massive membrane depolarization. Unlike PMB however, C(14)KKc(12)K was also bactericidal to Gram-positive bacteria (GPB) at or near the minimal inhibitory concentration (MIC), as assessed against a multispecies panel of >50 strains, displaying MIC(50) at 3 and 6 µM, respectively for GPB and GNB. C(14)KKc(12)K retained activity in human saliva, reducing the viability of cultivable oral microflora by >99% within two minutes of exposure, albeit at higher concentrations, which, nonetheless, were similar to the commercial gold standard, chlorhexidine. This equipotent bactericidal activity was also observed in pre-formed biofilms of Streptococcus mutans, a major periodontal pathogen. Such compounds therefore, may be useful for eradication of challenging poly-microbial infections.