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 colony-forming 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.