Antifungal effect of ophthalmic preservatives phenylmercuric nitrate and benzalkonium chloride on ocular pathogenic filamentous fungi

In the present study, the antifungal effects of phenylmercuric nitrate and benzalkonium chloride versus those of natamycin and ketoconazole were assessed against 216 filamentous fungi isolates from cases of fungal keratitis. They included 112 Fusarium isolates, 94 Aspergillus isolates, and 10 Alternaria alternata isolates. The strains were tested by broth dilution antifungal susceptibility testing of filamentous fungi approved by the Clinical and Laboratory Standards Institute M38-A document. The results showed that the MIC50 values of phenylmercuric nitrate were 0.0156, 0.0156, and 0.0313 μg/mL for Fusarium spp., Aspergillus spp., and A. alternata, respectively. The MIC90 values of phenylmercuric nitrate were 0.0313, 0.0313, and 0.0313 μg/mL for Fusarium spp., Aspergillus spp., and A. alternata, respectively. The MIC50 values of benzalkonium chloride were 16, 32, and 8 μg/mL for Fusarium spp., Aspergillus spp., and A. alternata, respectively. The MIC90 values of benzalkonium chloride were 32, 32, and 16 μg/mL for Fusarium spp., Aspergillus spp., and A. alternata, respectively. The study indicates that phenylmercuric nitrate has considerable antifungal activity and its effect is significantly superior to those of benzalkonium chloride, natamycin, and ketoconazole against ocular pathogenic filamentous fungi in vitro, deserving further investigation for treating fungal keratitis as a main drug.