Introduction

Contact lens wear is a significant risk factor for microbial keratitis accounting for some 50% of cases involving bacteria and fungi and 90% for the free-living amoeba Acanthamoeba. ^3,4 Poor hygiene practices such as defaulting on recommended hygiene procedures and rinsing or storing the lenses in tap water are recognised risk factors.³

Acanthamoeba tropozoite

Disinfection and cleaning are fundamental to safe contact lens wear. Multipurpose solutions (MPS) are the most commonly used systems for contact lens hygiene and comprise a single solution for rinsing, disinfecting and storing lenses. Whilst all contact lens disinfectants must demonstrate activity against bacteria and fungi, there are no requirements relating to their efficacy against Acanthamoeba or viruses.²

The efficacy of a new MPS, MeniCare Soft (Menicon Co., Ltd, Japan), against Acanthamoeba and viral pathogens was studied. Assays were developed to test the biocidal efficacy of the solution and also in its ability to remove organisms from soft contact lenses in “Rub & Rinse” or “No Rub & Rinse” procedures.

Methods

Test organisms. Poliovirus type 2 (PV-2), Herpes simplex virus type I (HSV-1) and Adenovirus type 8 (AV-8) were propagated in Hep-2 mammalian tissue culture cell line. Acanthamoeba polyphaga (Ros) and A. castellanii (ATCC 30868) trophozoites were maintained in a broth medium and encystment induced by addition of 50 mM MgCl2.¹

Test solutions and lenses. The MPS MeniCare Soft (Menicon Co., Ltd, Japan) was the test solution containing polyhexanide 0.0001%. Phosphate buffered saline (PBS) acted as the control. The soft contact lenses used were: Menicon MA, (ConventionaI), Menicon MeniSoft (Monthly replacement) CIBA Focus (Disposable).

Biocidal assays. Ten ml of test or control solution was challenged with Acanthamoeba or virus and samples removed after 0, 1, 2, 4, 6 and 24 hr exposure. The number of surviving organisms at each time point was determined by culture viability assays.¹

Regimen testing. Each lens was inoculated with 2 x 105 trophozoites, cysts or viral particles and left to adhere for 5 minutes. The lenses were then subjected to standard “Rub & Rinse” or “No Rub Rinse” cleaning and soaking for 4 hr in the MPS or PBS control. The number of viable organisms on the lenses was then determined by culture assays.¹

Results

Biocidal assays. The MPS gave a 3 - 4 log reduction (99.9 – 99.99% killing) in Acanthamoeba trophozoites after 4-6 hr. For the cysts, a 3 log reduction was found for A. polyphaga and 1.3 – 3.4 log for A. castellanii after 4-6 hr.

For the viruses, ≤1 log reduction occurred after 24 hr exposure.

Regimen testing. Following the “Rub & Rinse” or “No Rub & Rinse” protocols no surviving trophozoites or cysts of either Acanthamoeba spp. were recovered from any of the lens types and equates to a 5 log removal of the organism.

With the viruses, “Rub & Rinse” resulted in a 5 log removal of PV-2, HSV-1 and 4-5 log reduction for AV-8 from the lenses. With “No Rub & Rinse”, a 4-5 log removal in of the viruses was obtained.

Conclusions

• Standardised methods have been developed to test the efficacy of contact lens solutions against Acanthamoeba and viral pathogens in line with recommended procedures for bacteria and fungi.²
• MeniCare Soft was found to be active against Acanthamoeba in biocidal testing but not against viruses.
• Menicare Soft was effective in removing Acanthamoeba and viruses from soft contact lenses using “Rub & Rinse” and “No Rub & Rinse” regimens.
• Correct use of MPS contact lens solutions like MeniCare Soft may help reduce the incidence of microbial keratitis.

References

1. Borazjani, R.N. and Kilvington, S. (2005) Effect of a multipurpose contact lens solution on the survival and binding of Acanthamoeba species on contact lenses examined with a no-rub regimen. Eye Contact Lens 31, 39-45.
2. International Organization for Standardization: ISO 14729. (2001).  Ophthalmic optics-Contact lens care products-Microbiological requirements and test methods for products and regimens for hygienic management of contact lenses.
3. Kilvington, S., Gray, T., Dart, J., Morlet, N., Beeching, J.R., Frazer, D.G. and Matheson, M. (2004) Acanthamoeba keratitis: the role of domestic tap water contamination in the United Kingdom. Invest Ophthalmol Vis Sci 45, 165-9.
4. Radford, C.F., Minassian, D.C. and Dart, J.K. (2002) Acanthamoeba keratitis in England and Wales: incidence, outcome, and risk factors. British J Ophthalmol 86, 536-42.

This study was funded by Menicon Co., Ltd, Japan

Cytotoxicity and antimicrobial activity of the new MeniCare Soft multi-purpose soft contact lens disinfecting solution

Jacinto Santodomingo-Rubido, Osamu Mori, Satoshi Kawaminami
Menicon Co., Ltd., Nagoya, Japan

Purpose

Currently, multi-purpose contact lens solutions (MPDS) are the most widely prescribed regime for soft contact lens care. MPDS should provide a wide spectrum of disinfection against microorganisms without inducing toxicity to the eye. The cytotoxicity and antimicrobial activity of the new MeniCare Soft MPDS were compared with that of other commercially available MPDS.

Methods

The cytotoxicity & antimicrobial activity of MeniCare Soft (Menicon Co., Ltd., Nagoya, Japan) were compared with that of five commercially available MPDS: SOLOCARE AQUA^® (CIBA Vision Corporation, Duluth, GA, USA), Opti-Free Express (Alcon Laboratories, Fort Worth, TX, USA), ReNu MoistureLoc (Bausch & Lomb, Rochester, NY, USA), Complete Moisture Plus (Advanced Medical Optics, Santa Ana, CA, USA) & ReNu MultiPlus (Bausch & Lomb, Rochester, NY, USA). Table 1.

Cytotoxicity
V79 cells in 2ml medium were inoculated in well plates and culture for 24hrs. After inoculation, the medium was removed & 2ml of each diluted MPDS was added individually into wells at 1.25, 2.5, 5 & 10% concentrations with water for injection (negative control) & medium. Subsequently, the number of colonies was counted. The cytotoxicity of the different MPDS was expressed in terms of the concentration of MPDS that suppresses colony formation.

Antimicrobial activity
Antimicrobial activity was evaluated by means of the stand-alone contact lens disinfection test (ISO14729).1

Results

Figure 1. Cytotoxicity activity of the MPDS under investigation.
MeniCare Soft & Complete Moisture Plus were not cytotoxic at maximum concentration (10%). Cytotoxicity ranking of the other solutions was as follows: SOLOCARE AQUA^®< OptiFree Express< ReNu Multiplus< ReNu Moisture Lock.

Figure 2. Antimicrobial activity of the MPDS under investigation.
All MPDS met the primary criteria of the stand-alone test for bacterial species. ReNu MoistureLoc showed borderline values for Serratia marcescens and staphylococcus aureus.  Large differences on the fungal antimicrobial activity was found with the different MPDS under investigation. Complete MoisturePlus failed to meet the stand-alone test criteria for Fusarium solani.

Conclusions

MPDS with identical concentrations of PHMB can behave differently depending on solution formulation. Contact lens practitioners should feel confident in prescribing MeniCare Soft with any soft contact lens as it provides a high range of antimicrobial activity & lower cytotoxicity than many other MPDS.

References

1. International Organization for Standardization: ISO 14729. Ophthalmic optics-contact lens products-microbial requirements and test methods for products and regimes for hygienic management of contact lenses. 2001.