Three-Species Chronic Wound Model: Targeting Specific Species with Antibiotics

Abstract

This project involved growing three-species biofilms with Staphylococcus aureus (Sa10943), Pseudomonas aeruginosa (Pa215), and Clostridium perfringens (Cp816). E-test strip assays were conducted to determine antibiotic minimum inhibitory concentrations (MIC). The results revealed Pa215 was sensitive to gentamicin (MIC=3) and ciprofloxicin (MIC=0.38), Sa10943 was sensitive to gentamicin (MIC=0.25), and Cp816 was sensitive to tetracycline(MIC=8) and ciprofloxacin(MIC=0.15). Biofilms were grown in drip-flow reactors and treated with gentamicin (50 or 100 μg/ml) or ciprofloxacin (250μg/ml). The control biofilms had mean log cell densities (±standard deviation) of 8.94(±0.19), 10.71(±0.23), and 8.21(±0.24) for Sa10943, Pa215, and Cp816, respectively. Treatment with gentamicin at 50 µg/ml resulted in a 0.77(±0.53) log reduction (LR) for Sa10943 and no LR for the other species. Increasing the gentamycin concentration to 100 μg/ml resulted in similar LR of 0.88(±0.52) for SA10943, but additionally resulted in a LR of 1.10(±0.13) and 0.82(±0.26) for Pa215 and Cp816, respectively. Treatment with Ciprofloxacin at 250 μg/ml resulted in a LR of 0.73(±0.32), 1.62(±0.32), and 1.21(±0.32) for Sa10943, Pa215, and Cp816, respectively. Interestingly, these results showed that both Sa10943 and Cp816 showed antibiotic susceptibilities in the 3-species biofilms that were not predicted by the E-test.