Cysticidal effect on acanthamoeba and toxicity on human keratocytes by polyhexamethylene biguanide and chlorhexidine

To evaluate the cysticidal effect of polyhexamethylene biguanide (PHMB) and chlorhexidine on Acanthamoeba and its toxic effect on cultured human keratocytes.

Each well of a twofold-diluted Acanthamoeba cyst-containing suspension of 5 x 10(4) cysts/mL was treated with PHMB and chlorhexidine for 8, 24, and 48 hours to determine the minimal cysticidal concentration (MCC) of each disinfectant. Human corneal keratocytes (5 x 10(4) cells/mL) were exposed to PHMB and chlorhexidine for the same time to determine the survival rate of keratocytes. Inverted phase-contrast and electron microscopy were used to observe the morphologic changes.

The mean MCC of PHMB for 8, 24, and 48 hours was 9.42, 5.62, and 2.37 microg/mL, respectively. The mean MCC of chlorhexidine for 8, 24, and 48 hours was 24.32, 10.02, and 7.02 microg/mL, respectively. The respective survival rate of keratocytes at the MCC was 91.7%, 64.6%, and 49.7% for PHMB and 95.7%, 90.6%, and 78.1% for chlorhexidine, respectively. The cysts and keratocytes showed more damaged appearances after treatment with PHMB than chlorhexidine.

PHMB and chlorhexidine showed a similar amoebicidal efficacy. However, PHMB seemed to be more toxic to keratocytes than chlorhexidine.