Anthony Lam

Development of Standardized Methods for Assessing Biocidal Efficacy of Contact Lens Care Solutions Against Acanthamoeba Trophozoites and Cysts

PURPOSE To investigate experimental variables in the development of standardized methods to assess the efficacy of contact lens disinfection systems against the trophozoite and cysts of Acanthamoeba spp. METHODS A. castellanii (ATCC 50370), A. polyphaga (ATCC 30461), and A. hatchetti (CDC: V573) were adapted to axenic culture and used to produce cysts either with Neffs encystment medium (NEM) or starvation on nonnutrient agar (NNA). Challenge test assays and a most probable number approach were used to compare the trophozoite and cysticidal efficacy of four multipurpose disinfectant solutions (MPDSs) and a one-step hydrogen peroxide system (with and without the neutralizing step). RESULTS With trophozoites, four of four MPDSs and the one-step peroxide system gave ≥3 log₁₀ kill for all strains 6 hours, regardless of culture medium used. Greater resistance was found against cysts, with results for MPDSs varying by species and method of cyst production. Here, 1-3 log₁₀ kill was found with NEM cysts for three of four MPDSs compared with one of four for the NNA cysts at 6 hours (A. castellanii and A. polyphaga, only). The one-step peroxide system gave 1-1.9 log₁₀ kill with NEM cysts and 0.8-1.1 for NNA cysts. Only 3% hydrogen peroxide gave total kill (>3 log₁₀) of NNA cysts at 6 hours. CONCLUSIONS A reproducible method for determining the susceptibility of Acanthamoeba trophozoites and cysts to contact lens care systems has been developed. This will facilitate assay standardization for assessing the efficacy of such products against the organism and aid development of improved disinfectant and therapeutic agents.

Antimicrobial efficacy of multi-purpose contact lens disinfectant solutions following evaporation.

PURPOSE Non-compliance is a significant factor in contact lens related microbial keratitis and includes solution reuse and failure to recap the lens storage case resulting in evaporation effects. To address this, impact of partial evaporation on the antimicrobial efficacy of multipurpose contact lens care solutions was investigated. METHODS Solutions were evaporated under a stream of air to 2× and 4× concentration and challenged with Fusarium solani (ATCC 36031), Candida albicans (ATCC 10231) and Acanthamoeba castellanii (ATCC 50370). The level of organism kill at 6h was compared to the non-evaporated product. RESULTS ReNu with MoistureLoc(®) (RML) lost 90-100% of biocidal activity against C. albicans on evaporation, 75-99% for F. solani and 29-33% with A. castellanii at 2× or 4× concentration, respectively. OPTI-FREE(®) RepleniSH(®) lost 72-90% efficacy against C. albicans and F. solani, and 61% at 2× and 10% at 4× concentration with A. castellanii. ReNu(®) MultiPlus, AQuify(®) Multi-Purpose and Biotrue™ showed only loss in efficacy with C. albicans at 4× concentration giving 79%, 34.5% and 48% reduction, respectively. No loss in biocidal activity on evaporation was obtained with Complete(®) Revitalens for all organisms. CONCLUSION Partial evaporation can affect biocidal efficacy of multi-purpose solutions and may have been a significant factor in an outbreak of Fusarium keratitis cases associated with RML. Evaporation results in increased binding of cationic disinfectants to counter-ions in the formulation, reducing ability to attach and rupture anionic microbial cell walls. Interaction may also occur between the biocidal ingredient and other components, such as surfactants, resulting in sequestration of activity through micelle formation.

Resistance and Growth of fusarium species in Contact Lens Disinfectant Solutions

Purpose To compare the biocidal efficacy of contact lens care solutions against clinical isolates and the American Type Culture Collection (ATCC) 36031 reference strain of Fusarium species and to determine the ability of the organism to survive and grow in such systems. Methods The ISO 14729 reference method to assess biocidal efficacy was applied to the purified conidial form of 10 strains of Fusarium species. Six multipurpose disinfectant solutions (MPDSs), a one-step hydrogen peroxide (Per-1) system, a hydrogen peroxide–sodium chlorite (Per-2) system, and a one-step povidone iodine (PI) system were compared. Challenge organism viability was determined at various intervals, including the manufacturers’ recommended disinfection time for the products (4 to 6 hours) and thereafter to 21 days. Results All MPDSs achieved a 3- to 4-log10 reduction in viability of ATCC 36031 within the recommended disinfection time of 6 hours. For the clinical strains, MPDS-1 (PQ-1 + alexidine) and MPDS-2 (PQ-1 + PHMB) produced 3 to 5 log10 kill after 6 hours. Multipurpose disinfectant solution 3 (PQ-1 + Aldox 0.0006%), MPDS-4 (PQ-1 + Aldox 0.0005% + C-9 ED3A), and MPDS-5 (PQ-1 + Aldox 0.0005%) showed reduced efficacy for the same two strains, with 0.6 to 1.7 log10 kill. Multipurpose disinfectant solution 6 (PHMB) gave 1.6 log10 for one strain and 3 to 4 log10 for the remainder. Growth in all the MPDS was not detected up to 21 days incubation. Per-1 showed less than 1 log10 kill at 6 hours for six of 10 strains, including ATCC 36031, and growth (1.2 to 2.7 log10) occurred with three of 10 strains by 7 days. Per-2 gave less than or equal to 0.5 log10 kill after 6- or 24-hour exposure without growth. The PI system showed 4 to 5 log10 kill for all strains tested by the first time point of 4 hours. However, with the exception of ATCC 36031, growth (1.7 to 4.0 log10) occurred with all strains by 7 days in PI. Conclusions All MPDSs were effective against the ATCC 36031 reference strain of Fusarium solani. However, reduced efficacy was found for some MPDSs against the clinical isolates. Unlike MPDSs, peroxide- and povidone iodine–based systems have no continued antimicrobial presence once neutralized, and this can allow growth of surviving Fusarium in the solution. Accordingly, lenses should be subject to fresh disinfection if stored in such solutions for extended periods.

58 Biocidal efficacy of multipurpose contact lens disinfectant solutions against Acanthamoeba species

Purpose: To evaluate the efficacy of a new contact lens disinfecting solution. Method: The efficacy of a new contact lens disinfecting solution with a dual disinfection system was assessed against standard challenge microorganisms and clinical isolates of Acanthamoeba castellanii, Acanthamoeba polyphaga, Staphylococcus aureus, Pseudomonas aeruginosa, Serratia marcescens, Candida albicans, and Fusarium solani using stand-alone microbiological test methodology. Additionally, the efficacy of recently marketed contact lens care solutions, including Revitalens and Biotrue, was tested against standard challenge microorganisms. The stand-alone test is a time kill study designed to qualify individual solutions with a suitable level of antimicrobial activity as contact lens disinfection products. Results: After six hours of disinfection time, the OPTI-FREE EverMoist showed ∼2 logs kill against cysts of A. castellanii ATCC30234 and A. polyphaga ATCC 30871. OPTI-Free EverMoist met the primary Stand-alone criteria with efficacies of more than 4 log reductions for each of the three standard bacteria and each standard yeast and mold. All tested marketed contact lens care solutions showed efficacy against standard challenge microorganisms. Clinical isolates of Staphylococcus aureus, Pseudomonas aeruginosa, Serratia marcescens, and Candida albicans were reduced by approximately 4 logs or greater after six hours of exposure to OPTI-FREE EverMoist. Conclusions: OPTI-FREE EverMoist MPDS provides broad spectrum antimicrobial activity against a variety of challenge ATCC and clinical microorganisms. OPTI-FREE EverMoist leverages the proven PolyQuad® and Aldox® dual disinfection system to provide excellent antimicrobial efficacy.