Methods for Investigating Biofilm Inhibition and Degradation by Antimicrobial Peptides

Multidrug-resistant bacteria are a growing problem worldwide. One extensively studied resistance mechanism is biofilm colonization-microbial colonies formed by many Gram-positive and Gram-negative bacteria species. Cationic antimicrobial peptides (AMPs) are innate immune system molecules serving as a first line of defense in fighting invading pathogens. The AMPs' underlying mechanism and biophysical properties required for anti-biofilm activity are not fully known. Here we present protocols for investigating AMPs' biological activity against major stages of biofilm life cycle, namely, planktonic stage (MIC assay), initial adhesion to surfaces (bacterial attachment assay), and formation or degradation of sessile microcolonies (biofilm formation and degradation assays). Furthermore, we demonstrate experiments that allow determination and comparison between peptide biophysical properties (secondary structure, hydrophobicity, and oligomerization) and how they affect their mechanism (peptide-binding assays) of anti-biofilm activity.