Acanthamoeba polyphaga strain – causative agent of vision-threatening keratitis uncommonly detected in Poland, susceptible in vitro to toyocamycin

Introduction
Acanthamoebic keratitis, detected with increasing frequency worldwide in the last decades, mainly is reported in contact lens wearers. Other risk factors include damage to corneal cells, eye surgery and ocular exposure to water containing developmental forms of the amphizoic amoebae. In this study we analyzed Acanthamoeba isolates from complicated keratitis and evaluated some corneal strains in terms of their in vitro susceptibility to toyocamycin.

Material and methods
Six strains of Acanthamoebic keratitis in contact lens wearers, one with a history of swimming in a lake, previously improperly diagnosed and treated were analyzed. Acanthamoeba corneal isolates of T4 genotype cultured in vitro were monitored. A. polyphaga corneal strain and environmental A. castellanii Neff exposed to toyocamycin, the agent with an established anti-trichomonal and anti-toxoplasmal activity, were evaluated.

Results
A. polyphaga strain, which is not commonly diagnosed as an etiological agent of Acanthamoeba keratitis in Poland, was the most virulent in vitro. Amoebostatic effect of toyocamycin, without stimulation of encystation, was stronger for the corneal strain than for the environmental A. castellanii Neff.

Conclusions
There is no sufficient knowledge of the epidemiology of Acanthamoeba keratitis in Poland. Extremely high antimicrobial resistance of Acanthamoeba cysts leads to treatment failure, thus chemicals of possible anti-amoebic activity are still tested. Promising results of our study of adenosine analogue as the agent against Acanthamoebapathogenic strains justifies further tests with this drug and various amphizoic amoebic strains. This was the first study of in vitro susceptibility of corneal Acanthamoeba strain to toyocamycin.