In Vitro Evaluation of Antimicrobial Amyloidogenic Peptides for the Treatment of Early and Mature Bacterial Biofilms

Biofilm formation by pathogenic bacteria, including methicillin-resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa, and Escherichia coli, represents a major clinical challenge due to the high resistance of biofilms to conventional antimicrobial therapy. In this in vitro study, we investigated the antimicrobial and antibiofilm activity of synthetic peptides R23IT, R23LP, V31KT, R44KS, R44KP, V31KS, and I31KP against methicillin-resistant S. aureus (MRSA, SA180-F strain), S. aureus (129B), P. aeruginosa (2943), and E. coli (MG1655). In liquid medium, peptides R23LP and R44KS exhibited the broadest and most potent antimicrobial activity against all tested strains. On solid agar, these peptides demonstrated comparable activity, with notable effects particularly against E. coli. We further assessed the peptides’ impact on both early-stage and mature biofilms using crystal violet staining for total biomass and the MTT assay for cellular metabolic activity. Peptide R44KS showed a strong dose-dependent inhibitory effect on early MRSA biofilm formation, while most peptides unexpectedly enhanced biofilm formation by S. aureus and E. coli. Peptides R44KP and V31KS at 10 mg/mL significantly reduced both biomass and metabolic activity of early P. aeruginosa biofilms. None of the peptides inhibited mature biofilm biomass across species; however, several, particularly I31KP, significantly reduced the metabolic activity of MRSA within mature biofilms. These findings underscore the strain- and stage-specific effects of antimicrobial peptides and highlight R23LP, R44KS, R44KP, V31KS, and I31KP as promising candidates for targeted biofilm control in vitro, especially against MRSA.