Prevention of ESKAPE pathogen biofilm formation by antimicrobial peptides WLBU2 and LL37

Bacterial biofilm-dependent infections (e.g. cystic fibrosis, surgical sites, and medical implants) are associated with enhanced drug-resistance and are thus difficult to eradicate. The goal of this study was to systematically compare three distinct classes of antimicrobial peptides (AMPs) that include the clinically used antibiotic colistin, the natural AMP LL37, the engineered cationic-AMP WLBU2, and four commonly used antibiotics with different bactericidal mechanisms (tobramycin, ciprofloxacin, ceftazidime, and vancomycin) for biofilm prevention properties.

Using biofilm-prevention assays, we detected bacterial biomass post-attachment in subinhibitory concentrations (1/3 of the minimum inhibitory concentration [MIC]) for each AMP by the crystal violet method, to distinguish the commonly known bactericidal activity from potentially distinct mechanisms of biofilm prevention. Biofilm regulatory gene expression was assessed using RT-qPCR for correlation with biofilm growth inhibition.

Commonly used antibiotics at 1x MIC showed modest ESKAPE biofilm prevention while 1/3 MIC of AMPs demonstrated up to 90% biofilm prevention. WLBU2 was generally more effective in preventing bacterial attachment than colistin and LL37. Changes in bacterial biofilm regulatory gene expression were consistent with biofilm prevention.

The data warrant further exploration of AMPs with optimized structures to fill a knowledge gap on the potential application of AMPs for difficult-to-cure bacterial biofilm-related infections.