A-054. Salt and Osmolyte Effects on Chitosan-Arginine Activity against Pseudomonas aeruginosa PAO1 and Staphylococcus aureus MW-2

J. Uhrig1, A. Phang1, A. C. Parker1, S. J. Ryan2, S. M. Baker2,3, W. P. Wiesmann2, S. M. Townsend2, P. M. Orwin1;
1California State Univ., San Bernardino, CA, 2BioStarWest, Inc, Claremont, CA, 3Harvey Mudd Coll., Claremont, CA.

The discovery of novel antimicrobials with broad spectra of activity is important for the treatment of chronic diseases and nosocomial infections. In vitro, proprietary chitosan-arginine (CR) is bactericidal against Gram-negative and Gram-positive pathogens. Chitosan and its derivatives are proposed to function via perturbation of the cell membrane. However, the precise mode of CR action remains unclear. Pseudomonas aeruginosa often infects the lungs of patients with Cystic Fibrosis (CF) and causes various opportunistic infections. MRSA most frequently causes skin infections, but can be deadly if it enters the bloodstream. In this study, the efficacy of the antimicrobial chitosan-arginine (CR) was evaluated using P. aeruginosa PAO1 and community-acquired MRSA strain MW-2 following the addition of various chloride salts and non-ionic osmoprotectants to the cells. Osmolytes may reduce the efficacy of CR by protecting against cell membrane perturbation. Salts may additionally interfere directly with the charge interactions between CR and components of the cell surface, such as LPS, LTA, or phospholipid headgroups. Cells were treated with salt or osmolyte levels up to 250mM before and during CR exposure. In MW-2, we observed effects ranging from very little protection with KCl, to near complete protection with MgCl2. In PAO1, CaCl2 had the strongest protective effect, while no protection was observed with LiCl treatment of PAO1. MW-2 and PAO1 were both susceptible to CR in the presence of trehalose, demonstrating the importance of charge. This study suggests that positive charge correlates with protective effects and that CR may interact with negatively charged regions of the cell envelope, such as LPS, during bactericidal activity against PAO1. The mechanism of action against MRSA is likely also driven by interactions with charged surface moieties. Protective effects do not appear to be related to overall osmolyte concentration.