Modulation of Staphylococcus epidermidis (RP62A) extracellular polymeric layer by marine cyclic dipeptide-cyclo(l-leucyl-l-prolyl) thwarts biofilm formation

Staphylococcus epidermidis is the most frequent cause of biofilm mediated implant-associated infections. Extracellular polymeric substance (EPS) is a key component of most biofilms and in pathogens it specifically protects the entrenched-bacterial cells from antibiotics and hosts immune response, and thereby makes the infection ineradicable. Recently, the prominence of cyclic dipeptides in interfering with biofilms and the associated virulence factors of pathogens has offered an alternative to eliminate difficult-to-treat infections. Therefore, we assessed the effect of a potent antibiofilm agent cyclic dipeptide, cyclo(l-leucyl-l-prolyl) (CLP), on the EPS modification of S. epidermidis. The non-bactericidal antibiofilm efficacy of CLP against S. epidermidis was affirmed through quantitative (crystal violet and XTT assays) and qualitative (confocal and scanning electron microscopes) analyses. Notably, CLP was potent enough to reduce all the EPS components viz. polysaccharides, proteins and eDNA to a significant level. Substantial difference in the atomic composition and functionality of CLP treated EPS was evident through X-ray photoelectron spectroscopy. Furthermore, CLP dehydrated the S. epidermidis-EPS and altered the acetylated sugars as well as α-glycosidic linkage in it. The results of cyclic voltammetry (CV) indicate the decrease of total negative charge of EPS upon CLP treatment, which goes well in accordance with the decrease of eDNA. Thus, antibiofilm efficacy of CLP lies in its potency to alter the intrinsic functional groups and charge of secreted EPS.