Amoebicidal effects of contact lens disinfecting solutions.

PURPOSE: To compare the traditional manual hemacytometer method and an automated counter (Vi-cell) to enumerate and distinguish between viable and non-viable amoeba, and to determine the efficacies of contact lens (CL) disinfecting solutions against three species of Acanthamoeba. The efficacies in the presence of a bacterial food source and bovine serum albumin (BSA) were investigated. METHODS: Four brands of multipurpose solutions and a hydrogen peroxide disinfecting system (Oxysept) for soft CLs, and four disinfecting solutions for Rigid Gas Permeable (RGP) lenses were tested against three species of Acanthamoeba. Page's amoebic saline was included as a negative control and standard solutions of disinfecting agents, 6% hydrogen peroxide and 0.5% chlorhexidine, as positive controls. The effects of the presence of Pseudomonas aeruginosa and BSA on effectiveness were assessed. RESULTS: None of the CL solutions tested achieved a 1-log reduction in viability of all three Acanthamoeba species within the manufacturer's recommended disinfection times. The presence of P. aeruginosa did not significantly affect disinfecting capacity of multipurpose solution solutions but reduced activity of RGP solutions and the hydrogen peroxide system. BSA reduced trophozoicidal activity of all solutions. Bland and Altman analysis showed good agreement between Vi-cell and hemacytometer. CONCLUSIONS: The Vi-Cell analyzer offers a simple and effective method of determining amoebicidal activity. Our results show that the CL solutions tested could not satisfactorily kill Acanthamoeba.

Do multipurpose contact lens disinfecting solutions work effectively against non-FDA/ISO recommended strains of bacteria and fungi?

PURPOSE: Recent outbreaks of microbial keratitis have increased concerns about the efficacy of multipurpose solutions (MPS) against 'real-world' organisms. This study determined, in accordance with FDA/ISO standard methods, the effects of five MPS against clinical isolates and type strains of bacteria, and isolates of fungi from subjects' ocular structures; and of three MPS against environmental fungal isolates. METHOD: MPS were challenged with bacteria (type strains (ATCC) and clinical isolates of bacterial pathogens obtained from a district hospital laboratory) and with fungal isolates from both the periocular and conjunctival structures and from environmental air. RESULTS: All MPS demonstrated at least a 3-log reduction of challenged cell viability of all bacterial species tested, with the exception of MPS D against a canine infection Staphylococcus aureus isolate. Whilst all MPS tested were able to effect a 1.0-log reduction of viability of Fusarium solani (ATCC 36031), only two MPS had 90% viability reduction against all fungi of human origin and only one of these against all environmental fungal isolates. Effectiveness of these two solutions against fungal isolates compared to the remaining three MPS was found to be statistically significant (p = 0.003). CONCLUSIONS: All MPS demonstrated a 99.9% viability reduction against a wide range of bacteria including major ocular pathogens not currently included in the FDA panel. The inability of three MPS to achieve a 90% reduction against fungal isolates is of concern as there has been a recent upsurge in reports of fungal keratitis. We would recommend extension of the current FDA testing panel for MPS to include more fungal isolates.

Detection of acanthamoeba in tap water and contact lens cases using polymerase chain reaction.

PURPOSE: To detect the presence of Acanthamoeba in Hong Kong tap water and the contamination of contact lens cases using a polymerase chain reaction (PCR) method. METHODS: Tap water was collected from the bathroom sink of 100 households in Hong Kong and tested for the presence of Acanthamoeba by means of PCR amplification. Characteristics of homes were noted with respect to age, building type, and location. A sample of 100 contact lens cases were collected from regular users of contact lenses and tested for the presence of Acanthamoeba by PCR. RESULTS: Ten percent of water samples were contaminated by Acanthamoeba. The risk for contamination was higher in older properties, those located in the urban area of Kowloon, and those in which the bathroom tap was served by a water tank. Only one contact lens case yielded Acanthamoeba. The subject admitted poor compliance with lens care routines. CONCLUSIONS: Levels of Acanthamoeba detected using PCR were somewhat higher than previously reported in Hong Kong. Older plumbing and poorly maintained water storage tanks may increase the risk of Acanthamoeba contamination. Poor compliance with care of the lens case, allowing for the build up of biofilm may increase the risk of Acanthamoeba contamination of the case and possible Acanthamoeba keratitis.

Efficacy of multipurpose solutions for rigid gas permeable lenses.

The use of multipurpose solutions for cleaning and disinfecting rigid gas permeable lenses has replaced single purpose solutions, but there are no reports of the efficacy of these multipurpose solutions, or of the effects of storage conditions on their disinfecting capacities. This study investigated activity against four bacterial and two fungal species, and the effects of storage in a refrigerator, at room temperature, at elevated temperature in both dry and humid conditions and with exposure to sunlight. The disinfecting solutions were challenged with the micro-organisms initially upon opening and then at 2-weekly intervals up to 12 weeks after being stored under the different conditions. Solutions were opened daily to simulate use. One solution failed to meet Food and Drug Administration (FDA) criteria to reduce numbers of bacteria by three log dilutions and of fungi by one log dilution. Storage reduced activity of all solutions over the 12-week period, but not below the requirements of the FDA. Storage in the refrigerator tended to reduce disinfecting capacity more quickly. Multipurpose solutions for rigid gas permeable (RGP) lenses lose activity over the 3 months recommended time of use but remain satisfactory for use over this time in the conditions tested. Practitioners need to remind patients to replace their solutions regularly and should advise against storage in the refrigerator. Multipurpose solutions for RGP lenses have simplified cleaning and disinfecting processes and the current formulations have improved disinfecting capacity compared to former disinfecting solutions, which is particularly important for wearers of orthokeratology lenses.