Antimicrobial peptides: an effective approach to prevent bacterial biofilm formation in platelet concentrates

The safety of platelet concentrates (PCs) is a major concern in transfusion medicine due to contamination mainly with skin Gram-positive bacteria. The predominant contaminant, Staphylococcus epidermidis, forms bacterial cell aggregates (biofilms) in PCs posing a safety risk for transfusion patients. Combinations of synthetic antimicrobial peptides (AMPs) have demonstrated bactericidal activity in PCs. Herein, we have evaluated the ability of a mix of AMPs to inhibit biofilm formation and/or eradicate S. epidermidis biofilms.

Three synthetic AMPs, the platelet-derived peptide (PD4) and two arginine-tryptophan repeats (RW3 and RW4), were used for bactericidal and antibiofilm experiments in glucose-supplemented trypticase soy broth (TSBg) and PCs spiked with three biofilm-forming strains of S. epidermidis. Time-killing assays were performed to evaluate the bactericidal capability of the peptides. Inhibition of biofilm formation was assayed by seeding S. epidermidis into TSBg or PC cultures supplemented with the AMPs. Biofilm eradication assays were performed after AMP treatment of preformed biofilms with and without mechanical dislodging. Biofilms were measured using a crystal violet assay.

Time-killing assays demonstrated that all S. epidermidis strains were eliminated after 24 hours of AMP treatment. While inhibition of biofilm formation was observed for all S. epidermidis strains in TSBg and PCs, the AMP treatment was only effective to reduce the bacterial load of mechanically dislodged biofilms.

The combination of three synthetic AMPs (PD4-RW3-RW4) can be used to inhibit biofilm formation by S. epidermidis to enhance PC safety. However, further investigation is needed to improve their activity against mature S. epidermidis biofilms.