A Structurally Defined C12-Alkyl Quaternary Ammonium Compound reduces bacterial burden and biofilm in an infected wound model

Abstract

BackgroundMethicillin-resistant Staphylococcus aureus (MRSA) remains a common cause of skin and soft tissue infections, and topical agents that combine antimicrobial activity with wound compatibility are needed. C12-alkyl(ethylbenzyl)dimethyl ammonium chloride is a novel C12 quaternary ammonium molecule (hereafter, EQ12) related to benzalkonium chloride but designed to avoid the compositional heterogeneity and varied potency of conventional C8-C18 benzalkonium mixtures. We evaluated whether topical EQ12 is tolerated in healing wounds and whether it reduces MRSA burden in a splinted murine excisional wound infection model. MethodsFemale CD1 mice underwent 5-mm full-thickness dorsal excisional wounding, silicone splinting, and transparent dressing placement. For tolerability studies, uninfected wounds received EQ12 at 0.1 or 1 mg/mL or phosphate-buffered saline (PBS) and were followed for 14 days. For efficacy studies, wounds were inoculated with 1 x 104 CFU MRSA and treated topically every 8 hours for 3 days beginning 4 hours after infection with EQ12 (1 mg/mL), bacitracin (500 U/mL), or PBS. Wound tissues were harvested on days 2, 4, and 6 for quantitative culture. Dressing-associated biofilm was evaluated by scanning electron microscopy. ResultsEQ12 did not alter body weight, wound inflammation scores, wound area, or percent wound closure compared with PBS in uninfected animals. In infected wounds, day 2 tissue burdens were not significantly different among treatment groups. By day 4, EQ12 significantly reduced MRSA burden compared with PBS, whereas bacitracin did not. By day 6, EQ12-treated animals had significantly lower MRSA burdens than both bacitracin- and PBS-treated controls. Mean tissue burden in the EQ12 group declined from 6.27 log10 CFU/g on day 4 to 5.53 log10 CFU/g on day 6, while bacitracin- and PBS-treated wounds remained persistently colonized. SEM revealed minimal adherent cocci or matrix-like bridging on dressings from EQ12-treated wounds, in contrast to dense microcolonies and biofilm-like structures on bacitracin and PBS dressings. ConclusionsTopical EQ12 was compatible with gross wound healing and reduced MRSA burden in a dressed, splinted murine wound model. These data support continued development of EQ12 as a topical anti-staphylococcal wound-directed antimicrobial.