Effect of 2, 6-Dichlorobenzonitrile on Amoebicidal Activity of Multipurpose Contact Lens Disinfecting Solutions

Multipurpose contact lens disinfecting solutions (MPDS) are widely used to cleanse and disinfect microorganisms. However, disinfection efficacy of these MPDS against Acanthamoeba cyst remain insufficient. 2, 6-dichlorobenzonitrile (DCB), a cellulose synthesis inhibitor, is capable of increasing the amoebical effect against Acanthamoeba by inhibiting its encystation. In this study, we investigated the possibility of DCB as a disinfecting agent to improve the amoebicidal activity of MPDS against Acanthamoeba cyst. Eight commercial MPDS (from a to h) were assessed, all of which displayed insufficient amoebicidal activity against the mature cysts. Solution e, f, and h showed strong amoebicidal effect on the immature cysts. Amoebicidal efficacy against mature cysts remained inadequate even when the 8 MPDS were combined with 100 μM DCB. However, 4 kinds of MPDS (solution d, e, f, and h) including 100 μM DCB demonstrated strong amoebicidal activity against the immature cysts. The amoebicidal activity of solution d was increased by addition of DCB. Cytotoxicity was absent in human corneal epithelial cells treated with either DCB or mixture of DCB with MPDS. These results suggested that DCB can enhance the amoebicical activity of MPDS against Acanthamoeba immature cyst in vitro.

Evaluation of Cysticidal Effects of Contact Lens Disinfectant on Acanthamoeba Isolates

PURPOSE: To evaluate the cysticidal effect of 5 kinds of commercially available contact lens disinfectants against 2 clinical isolates of Acanthamoeba. METHODS: Five kinds of commercially available contact lens disinfectants were soaked with cysts of Acanthamoeba ludgdunesis and castellanii at the concentration of 10(3), 10(4), and 10(5) cells/ml for 1 and 4 or 6 hours. Cysts which were not excysted in 7 days after treatment were recognized to be killed. Morphologic changes were evaluated by electron microscopic observation. RESULTS: Contact lens disinfectants which contain myristamidopropyl dimethylamine (MAPD) showed the best cysticidal effect. These disinfectants demonstrated a cysticidal effect on both Acanthamoeba species of all concentrations in 6-hour treatment. Contact lens disinfectants which contain polyhexamethylene biguanide (PHMB) did not demonstrate cysticidal effect, except for Acanthamoeba castellanii at the concentration of 10(3) cells/ml, in either 4- or 6-hour treatment. Separation of plasma membrane from endocyst and damage of organelles were prominent in cases showing a cysticidal effect. CONCLUSIONS: Contact lens disinfectant which contains MAPD may be helpful in preventing the Acanthamoeba keratitis. A higher concentration of PHMB is required to be effective in preventing Acanthamoeba keratitis.