Evaluating the Biocidal Efficacy of Multi-purpose and Hydrogen Peroxide Solutions Against Fungal Isolates Associated with Ocular Infection

Abstract

Purpose: : The biocidal efficacy of several multi-purpose solutions (MPS) and hydrogen peroxide solutions (H2O2) were evaluated against fungal isolates (including multiple strains of Candida albicans, C. tropicalis, Fusarium oxysporum, and F. solani) known to be associated with microbial keratitis.

Methods: : Testing was performed on six MPS and two H2O2, all within expiry, to evaluate biocidal efficacy according to ISO standard 14729:2001/(Amendment 1):2010(E), modified to include organic soil in the preparation of the clinical isolates; and measuring biocidal efficacy only at the minimum recommended disinfection time point for each product. Challenge organisms had been isolated from clinical sources. Clinical isolates were prepared by using ~5X10⁵ colony forming units (cfu)/ml as the challenge inoculum for separate tests on each solution. Three separate lots of solution were tested against each isolate.

Results: : Biocidal efficacy results ranged from no effect (0.0 log reduction from initial challenge levels) to > 4.0 log reduction for some solutions/isolates. ISO 14729 primary acceptance criteria (minimum 1.0 log reduction for yeasts and molds) were used as a guide for demonstrating efficacy in this non-compendial testing against the challenge organisms. Four solutions demonstrated efficacy against all of the challenge isolates. Of the remaining solutions, two were effective against >70% of the isolates, one was effective against 47% of the isolates, and one solution did not demonstrate efficacy by this measure against any of the challenge organisms. Mean overall log reductions per solution ranged from 3.0 or greater for three of the solutions; 2.0-2.9 for three of the solutions, 1.0 for one, and 0.2 for the last solution. Solutions showed strengths and weaknesses against different genera.

Conclusions: : The results show that using clinical isolates can help distinguish in vitro performance differences of various MPS and H2O2. The use of methodology based on a modification of the ISO 14729 standard provides data that are easily understood and can be used to characterize the biocidal efficacy of solutions. Further study is needed to determine if these in vitro results could suggest clinical significance.

Keywords: fungal disease • antibiotics/antifungals/antiparasitics • contact lens