Biofilm formation by Enterococcus faecalis on intraocular lens material

Abstract

Abstract: : Purpose: As biofilms have received increasing attention as the cause of highly refractory infections, including those of the eye, the aim of this study was to compare the ability of Enterococcus faecalis to form biofilms on various intraocular lens (IOL) materials. Methods: Ten isogenic Enterococcus faecalis strains varying in pathogenic potential [cytolysin (Cyl) positive and negative, enterococcal surface protein (Esp) +/– in background FA2–2, Esp +/– in the wild type background (WT), and strains varying in both Cyl and Esp] were used to seed biofilms. Biofilms were cultivated on sample disks (6.0mm dia. X 1.0mm) of various (silicone, polymethylmetacrylate, acrylic) IOL materials in Tryptic Soy Broth with glucose. Biofilms were allowed to form on these materials in wells of 96–well flat–bottomed plate with containing the disks. After 24, 48, or 72 hours, biofilms were stained with crystal violet. The optical density (OD₅₉₀) of crystal violet extracted from the stained biofilms was then measured as an index of the extent of biofilm formation. Further, glass beads were used to dissociate the organisms in the biofilms, and the number of colony forming units (CFU) contained in each biofilm were determined. Results: All strains formed biofilms on each of the surfaces by 24 hours. The three Esp positive strain showed significantly greater biofilm formation (OD₅₉₀ 0.42–0.48) than isogenic mutant strains on all materials tested (p<0.001). Between materials, however, there was no significant difference in the quantity of biofilm formed as measured by crystal violet staining. The increase in biofilm observed on all materials for ESP positive strains was also reflected in increased numbers of CFU (log₁₀ 7.01–7.12 CFU/ml). Conclusions: The phenotype of E. faecalis strains significantly impacts the ability to form biofilms on IOL materials. However, the extent of biofilm formation on materials of various composition was observed to be similar.

Keywords: microbial pathogenesis: experimental studies • endophthalmitis • bacterial disease