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2021 OMIG Abstract

Antiamoebic Susceptibility Differences of Acanthamoeba Cysts in Indian and US Isolates

Quintin Richardson, Maya Talbott, Vicky Cevallos, Lalitha Prajna, Gerami D Seitzman,
Thomas M Lietman, and Jeremy D Keenan
F.I. Proctor Foundation at the University of California, San Francisco, San Francisco, California

Purpose: Outcomes of Acanthamoeba keratitis are often worse in India than in the US. Although this may be due to delays in diagnosis, it is also possible that inherent differences in the organisms on each continent are responsible. The goal of the present study was to determine whether antiamoebic susceptibility patterns were different when comparing Acanthamoeba isolates from India to those of the US.

Methods: Acanthamoeba isolates were obtained from corneal scrapings from patients with infectious keratitis at the F.I. Proctor Foundation (San Francisco, CA) and Aravind Eye Hospital (Madurai, India) from 2008 to 2012. A previously described minimum cysticidal concentration (MCC) assay was performed by a single laboratory technician at Aravind to assess susceptibility to five anti-amoebic agents for all isolates. Testing was done in triplicate, with the median MCC chosen for analyses.

Results: The susceptibility assay was performed on 23 Acanthamoeba isolates from Proctor and 20 isolates from Aravind. The MCC (μg/mL) for polyhexamethylene biguanide (PHMB) was 6.25 [IQR 5.47-12.5] for the Aravind isolates and 6.25 [IQR 6.25-9.375] for the Proctor isolates (p=0.75); for chlorhexidine was 6.25 [IQR 3.125-6.25] for the Aravind isolates and 3.125 [IQR 3.125-9.375] for the Proctor isolates (p=0.81); for voriconazole was 2500 [IQR 2500-5000] for the Aravind isolates and 5000 [IQR 1250-20000] for the Proctor isolates (p=0.25); for hexamidine was 15.6 [IQR 15.6-39.0625] for the Aravind isolates and 15.6 [IQR 15.6-31.25] for the Proctor isolates (p=0.92); and for propamidine was 15.6 [IQR 7.81-15.6] for the Aravind isolates and 15.6 [IQR 7.81-31.25] for the Proctor isolates (p=0.42).

Conclusions: This study found no statistically significant differences in antiamoebic susceptibility when comparing Acanthamoeba keratitis isolates from Indian vs. US samples. These findings suggest that differences in antiamoebic susceptibility are likely not responsible for differential outcomes in Acanthamoeba keratitis between the two locations.

Disclosure: N

Support: This study was supported by the National Institutes of Health, Bethesda, Maryland (grant no.: R34EY022368); and Research to Prevent Blindness, Inc, New York, New York (unrestricted departmental funding)

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