Acanthamoeba griffini. Molecular characterization of a new corneal pathogen

Acanthamoeba was isolated from the cornea of a soft contact lens wearer who had keratitis. The protozoan was also isolated from the contact lens storage case and the domestic water supply used to clean the case. Using morphologic features, all three isolates were identified tentatively as A. griffini, a species not previously associated with keratitis. Complete small subunit ribosomal RNA gene (18S rDNA) sequence analysis was used to characterize further the three isolates. 18S rDNA was polymerase chain reaction-amplified from whole cell DNA derived from amoebal lysates. The genes were cloned and sequenced. Complete sequences of approximately 2800 base pairs were obtained from each culture and compared wih those stored in a data base for homologous Acantamoeba sequences. The isolates were unequivocally identified as A. griffini both by comparison of the gene sequence available for the type strain of the species and the presence of a unique group I intron located within the small subunit rDNA. Sequences obtained for the three isolates were identical, indicating that they were the same strain. The first direct connection between human disease and A. griffini is reported from a case of Acanthamoeba keratitis. The type strain of this species was isolated from a marine environment, but the disease-causing strain ws isolated from a domestic water supply. The DNA sequences obtained confirmed unequivocally the epidemiologic association between a keratitis-causing strain of Acanthamoeba, the contact lens storage case, and the domestic water supply.