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Updated: Apr 28, 2026
Author Spotlight: Studying Behavior of Acanthamoeba to Develop Targeted Strategies for Preventing Acanthamoeba Keratitis
Published on: September 20, 2024
In vitro evaluations of topical agents to treat Acanthamoeba keratitis
Atsuko Sunada1, Keigo Kimura2, Isao Nishi2
1Department of Medical Technology, Osaka University Hospital, Osaka, Japan; Department of Biomedical Informatics, Division of Health Sciences, Osaka University Graduate School of Medicine, Osaka, Japan.
Purpose:
To evaluate the effectiveness of topical agents for the treatment of Acanthamoeba keratitis (AK).
Design:
Laboratory research.
Participants:
Fifty-six Acanthamoeba isolates from 56 patients with clinically proven AK were studied.
Methods:
The effectiveness of 7 agents against Acanthamoeba cysts was determined in vitro. The agents were 1.0% povidone-iodine, 0.05% benzalkonium chloride (BZC), 0.02% chlorhexidine gluconate (CHG), 0.1% propamidine isethionate, 0.02% polyhexamethylene biguanide (PHMB), 5.0% natamycin, and 1.0% voriconazole (VRCZ). These concentrations are those recommended for patients. In addition, 10-fold dilutions of each of the agents were tested. After exposing the cysts to each agent at 35°C for 1 hour or 24 hours, the agents were removed by centrifugal washing. The exposed cysts were observed by optical microscopy for 7 days. In addition, the fine structures of the exposed isolates were examined by transmission electron microscopy (TEM). The genotype of the isolates was determined by 18S rDNA fragment sequencing.
Main Outcome Measures:
The in vitro susceptibility was determined by complete growth inhibition, and the morphologic appearance was determined by TEM. The genotypes of the 56 isolates were determined by 18S rDNA fragment sequencing.
Results:
The Acanthamoeba cysts were most susceptible to natamycin, followed by povidone-iodine, BZC, PHMB, propamidine, and CHG. None of the strains was susceptible to VRCZ. The susceptibilities to PHMB and CHG may be time dependent and to propamidine may be concentration dependent. Transmission electron microscopy showed changes in the inner structure of the cysts exposed to natamycin and povidone-iodine. The Acanthamoeba genotype was T4 in 52 isolates, and cysts with the same genotype had different agent susceptibilities.
Conclusions:
Natamycin and povidone-iodine had excellent cysti-static (or cystcidal) effects, and PHMB and propamidine did not. There was no correlation between agent effectiveness and Acanthamoeba genotype. Therefore, susceptibility tests of isolates are needed to choose the most appropriate agent, and our results can be a guideline for choosing the most appropriate agent for immediate empirical treatment of AK.
