Differences Among Strains of the Fusarium oxysporum-F. solani Complexes in Their Penetration of Hydrogel Contact Lenses and Subsequent Susceptibility to Multipurpose Contact Lens Disinfection Solutions

Abstract

To examine in vitro conditions for attachment and penetration of silicone hydrogel (SH) lenses by clinical isolates of the Fusarium oxysporum-F. solani complexes and the relative susceptibilities of the fusaria in the lens matrices to multipurpose contact lens solutions (MPSs). SH soft contact lenses were soaked in Sabouraud dextrose broth (SAB) for 2 hours and transferred to 3.0 mL of phosphate-buffered saline (PBS). The lenses were inoculated with representative isolates of both complexes and incubated on a shaker at ambient temperature. Lenses were examined daily by light microscopy before and after rinsing and rubbing in MPS. Selected lenses penetrated by fungi were rinsed and rubbed with MPS and held in MPS for 6 hours, transferred to PBS with 0.03% SAB, and examined daily. The degree and rate of lens penetration of contact lenses by isolates of the F. oxysporum-F. solani complexes varied with lens type and the strain. Isolates obtained from patients with Fusarium keratitis produced on and within lenses chlamydospores that seemed similar to those observed in lenses actually worn by patients when they developed Fusarium keratitis. Clinical isolates showed greater capacities than those of a standard test strain to penetrate lenses and to survive exposures to various MPSs. In general, isolates of F. solani were more readily removed from lenses by rubbing than were isolates of F. oxysporum. The ability of Fusarium spp. to attach to and penetrate SH lenses in vitro varies with the lens type and strain, and this ability may make infectious keratitis more likely. We recommend the incorporation of a rubbing step in the MPS disinfection of hydrogel lenses to reduce the risk of fungal keratitis.