Antimicrobial susceptibility of 19 Australian corneal isolates of Acanthamoeba

Purpose: To determine the in vitro drug susceptibility of Australian cornea l isolates of Acanthamoeba and to correlate the results with patient treatm ent and visual outcome. Methods: Acanthamoeba isolates were obtained from a reference laboratory. C yst suspensions were prepared from 19 strains and exposed to 10 antimicrobi al agents for 7 days. The minimum drug concentrations required to inhibit e xcystation were determined. Inhibited cells were then plated out to determi ne minimum cysticidal concentrations. Results: Overall, propamidine proved to be the most active anti-Acanthamoeb a agent tested. The disinfectant polyhexamethylene biguanide, either pure o r in Baquacil, was also effective. Pentamidine, hexamidine, chlorhexidine a nd chloroxylenol had intermediate activity, while neomycin, amphotericin B and povidone-iodine had poor activity. There was no clear relationship betw een in vitro susceptibility and visual outcome. Conclusions: Propamidine and polyhexamethylene biguanide drops are recommen ded as initial choices for the treatment of Acanthamoeba keratitis. The var iability in the susceptibility to any one agent suggests that individual te sting of isolates is necessary to identify the most appropriate treatment. A number of factors influence visual outcome in these cases; further studie s are required to resolve the importance or otherwise of in vitro susceptib ility.