[Comparison of the activities of silver nitrate with those of three antifungal agents against ocular pathogenic fungi in vitro].

OBJECTIVE

To investigate antifungal activity of silver nitrate compared with fluconazole, ketoconazole and amphotericin B against ocular pathogenic fungi in vitro.

METHODS

It was an experimental study. Susceptibility tests were performed against 260 isolates (15 genera and 29 species) of ocular pathogenic fungi by broth dilution antifungal susceptibility testing of filamentous fungi (M38-A) approved by National Committee for Clinical Laboratory Standards (NCCLS). Final concentrations ranged from 0.031 to 16.000 mg/L for silver nitrate, ketoconazole and amphotericin B, from 0.5 - 256.0 mg/L for fluconazole. Minimum inhibitory concentration (MIC) was defined as the lowest drug concentration that showed absence of growth or complete growth inhibition (100%). The end points were determined as 100% growth inhibition for silver nitrate and amphotericin B, and > or = 75% growth inhibition for ketoconazole and fluconazole.

RESULTS

The MICs at which 90% of isolates were inhibited (MIC(90)) of silver nitrate, ketoconazole, amphotericin B and fluconazole were 2.000, 512.000, 32.000 and 2.000 mg/L for Fusarium species, respectively; 1.000, 256.000, 2.000 and 2.000 mg/L for Aspergillus species, respectively; 2.000, 128.000, 4.000 and 2.000 mg/L for Alternaria alternate, respectively; 2.000, 4.000, 0.125 and 0.500 mg/L for Curvularia lunata, respectively; and 1.000, 256.000, 1.000 and 1.000 mg/L for unusual ocular pathogens, respectively. Silver nitrate was highly active against Aspergillus species (92.9% susceptible at a MIC of < or = 1.0 mg/L) and Fusarium species (96.3% susceptible at a MIC of < or = 2.0 mg/L). 95.6% of Fusarium species and 90.8% of Aspergillus species exhibited resistance to fluconazole, 44.1% of Fusarium species and 42.9% of Aspergillus species exhibited resistance to amphotericin B, 66.2% of Fusarium species exhibited resistance to ketoconazole. The activity of silver nitrate against the fluconazole-resistant, ketoconazole-resistant and amphotericin B-resistant strains was high.

CONCLUSION

Silver nitrate has promising activity against a wide variety of ocular pathogenic fungi in vitro, and may have a role in future studies of antifungal eye drops and treating fungal keratitis.