Antibiotic Efficacy against Methicillin-Susceptible Staphylococcus aureus Biofilms on Synthetic and Biological Vascular Grafts

Background: Biofilm formation is one of the greatest challenges encountered in vascular graft infections. Our aim is to compare the efficacy of 5 antibiotics against methicillin-susceptible Staphylococcus aureus (MSSA) biofilms on the surface of 4 vascular grafts. Methods: In vitro study of 2 clinical MSSA strains (MSSA2 and MSSA6) and 4 vascular grafts (Dacron, Dacron-silver-triclosan (DST), Omniflow-II, and bovine pericardium). After a 24-hr incubation period, the graft samples were divided into 6 groups: growth control (no treatment), ciprofloxacin 4.5 mg/L, cloxacillin 100 mg/L, dalbavancin 300 mg/L, daptomycin 140 mg/L, and linezolid 20 mg/L. Quantitative cultures were obtained and results expressed as log10 colonyforming units per milliliter (CFU/mL). Analysis of variance was performed to compare biofilm formation between the different groups. Results: The mean +/- standard deviation MSSA2 count on the growth control Dacron graft was 10.05 +/- 0.31 CFU/mL. Antibiotic treatment achieved a mean reduction of 45%; ciprofloxacin was the most effective antibiotic (64%). Baseline MSSA2 counts were very low on the DST (0.50 +/- 1.03 CFU/mL) and Omniflow-II (0.33 +/- 0.78 CFU/mL) grafts. On the bovine pericardium patch, the count was 9.87 +/- 0.50 CFU/mL, but this was reduced by a mean of 45% after antibiotic treatment (61% for ciprofloxacin). The mean MSSA6 count on the growth control Dacron graft was 9.63 +/- 0.53 CFU/mL. Antibiotics achieved a mean reduction of 48%, with ciprofloxacin performing best (67% reduction). The baseline MSSA6 count on the DST graft was 8.54 +/- 0.73 CFU/mL. Antibiotics reduced biofilm formation by 72%; cloxacillin was the most effective treatment (86%). The MSSA6 count on the untreated Omniflow-II graft was 1.17 +/- 1.52 CFU/mL. For the bovine pericardium patch, it was 8.98 +/- 0.67 CFU/mL. The mean reduction after antibiotic treatment was 46%, with cloxacillin achieving the greatest reduction (68%). Conclusions: In this in vitro study, ciprofloxacin and cloxacillin performed best at reducing biofilms formed by clinical MSSA strains on the surface of biological and synthetic vascular grafts.