Effects of contact lens solution disinfectants against filamentous fungi.

Purpose: To assess and compare the antifungal activity of polyhexamethylene biguanide (PHMB), thimerosal, cetylpyridinium chloride, and chlorhexidine, which are disinfectants used in multipurpose disinfectant solutions (MPDSs) against ocular pathogenic Fusarium solani and Aspergillus flavus isolates in vitro.

Methods: The in vitro activity of PHMB, thimerosal, cetylpyridinium chloride, and chlorhexidine was assessed against 40 isolates of ocular pathogenic fungi that included 24 F. solani and 16 A. flavus isolates. The strains were tested by broth dilution antifungal susceptibility testing of filamentous fungi approved by the CLSI (Clinical and Laboratory Standards Institute) M38-A document.

Results: MIC90 (minimum inhibitory concentration for 90% of the organisms) values of PHMB were 4 and 16 μg/mL for F. solani and A. flavus, respectively. MIC90 values of thimerosal were 0.0313 and 0.0625 μg/mL for F. solani and A. flavus, respectively. MIC90 values of cetylpyridinium chloride were 2 and 2 μg/mL for F. solani and A. flavus, respectively. MIC90 values of chlorhexidine were 32 and 32 μg/mL for F. solani and A. flavus, respectively.

Conclusions: As a disinfectant used in MPDSs, thimerosal showed the highest levels of antimicrobial activity against ocular pathogenic F. solani and A. flavus isolates. The concentrations of PHMB (0.0001%), cetylpyridinium chloride (0.00014%), and chlorhexidine (0.003%) in MPDSs are sublethal levels for ocular pathogenic F. solani and A. flavus isolates. Although multiple ingredients within MPDSs play a role in antimicrobial efficacy, antimicrobial activity may be significantly influenced by the disinfectants used in the solution formulations.