In addition to assessing their anti-microbial activities, the capabilities of the peptides to inhibit S. aureus biofilm formation were tested. Biofilm formation by S. aureus is clinically relevant because biofilm formation allows pathogens to adhere to and accumulate on scabs or in-dwelling medical devices, such as catheters. Furthermore, in addressing wound infections, biofilm-embedded bacteria are often more difficult to combat than bacteria in planktonic form. This difficulty applies to both antibiotic regimes

and the host immune response [38, 39]. Thus, it would be beneficial to prevent biofilm production BMN 673 chemical structure as part of wound treatment. NA-CATH:ATRA1-ATRA1 proved effective at inhibiting biofilm formation at concentrations much lower than is required to reduce bacterial

growth under high salt conditions. These Erismodegib datasheet findings are important, as there are few reports of AMPs or other antimicrobials exerting anti-biofilm activity against S. aureus at sub-anti-microbial concentrations. This suggests that these peptides may act internally on the bacteria, affecting the expression of genes that are essential for the development of biofilm [15, 32]. For example, in S. aureus, production of PNAG polysaccharide, which is a major component of the biofilm matrix, is regulated by genes of the agr locus [40] (in response to an autoinducer peptide, AIP) and the ica locus [41]. In addition, a critical role for Bap (biofilm-associated protein) has been demonstrated for biofilm formation by this bacterium, with Bap and genomic DNA (or eDNA) contributing to the strength of the biofilm. In Monoiodotyrosine Pseudomonas aeruginosa, the human cathelicidin LL-37 alters the expression of

biofilm related genes such as Type IV pili, Rhamnolipid and Las quorum sensing system at sub-antimicrobial levels [32]. Staphylococcus aureus lacks these genes, and the molecular and genetic targets of LL-37 against S. aureus remain undefined. By performing biofilm attachment experiments against S. aureus, we were able to determine that NA-CATH:ATRA1-ATRA1 and its parent peptide, NA-CATH, inhibit biofilm but not by inhibiting attachment. D- and L-LL-37 peptides are capable of inhibiting initial biofilm attachment (58-62%), suggesting a potential interaction of these peptides with bacterial adhesins may be part of their mechanism. We have not yet determined the bacterial target of NA-CATH:ATRA1-ATRA1 or the D- and L-LL-37 peptides in S. aureus, but we intend to investigate this further in future work. One mechanism could be by directly promoting biofilm dispersal (as has been observed for some cationic detergents such as cetylpyridinium chloride [42]) or by inhibiting attachment. It is unlikely that the mechanism involves killing the bacteria, since we have observed that bacterial growth under high-salt conditions is not affected by these peptides. Moreover, anti-biofilm activity was observed for peptides associated with poor anti-microbial effect such as D-LL-37.