Differences in the Cysticidal Activity of Topical Agents against Three Genotypes of Acanthamoeba Isolated from Patients with Keratitis
To evaluate the effectiveness of topical agents to treat keratitis caused by Acanthamoeba strains with genotypes T3, T4, and T11 and to clarify the minimum cysticidal concentration (MCC) of anti-amoeba agents. Nine acanthaomoeba strains were isolated from patients with keratitis. Of the nine isolates, one belonged to the T3 genotype, one to the T11 genotype, and the seven to the T4 genotype. The effectiveness of seven agents against Acanthamoeba cysts was determined in vitro. Chlorhexidine gluconate (CHG), polyhexamethylene biguanide (PHMB), benzalkoniumchloride(BZC), povidone-iodine, natamycin, and gatifloxacin were diluted with sterile distilled water by the double dilution method while Artemisinin was diluted with anhydrous alcohol. Dexamethasone sodium phosphate was used to test the ameboebicidal activity of steroids. Transmission electron microscopy showed that PHMB, BZC, CHG, povidone-iodine, and artemisinin made destructive changes in the morphology and structures of the cysts. Agent effectiveness assays showed that all nine of the Acanthamoeba isolates were susceptible to CHG, PHMB and BZC, with an average MCC of 0.37%, 0.08%, and 0.013%, respectively. ANOVA testing showed that CHG, PHMB, and BZC had significant differences in activity against Acanthamoeba (F=17.294, P=0.000). There was no significant difference in CHG, PHMB, and BZC susceptibility among the T11, T3, and T4 genotypes. Of note, one of the T3 Acanthamoeba isolates had high susceptibility to artemisinin, with a MCC of 0.008g/ml. For all of the Acanthamoeba isolates, the cysticidal rate of PHMB, CHG, and BZC was lower when dexamethasone sodium phosphate was added. PHMB and BZC showed the strongest amoebicidal activity; followed by CHG. Artemether may be a promising novel drug for the treatment of Acanthameoba keratitis. Steroids should not be used to treat Acanthamoeba keratitis (AK) unless the infection is controlled.