Discrimination between clinically relevant and nonrelevant Acanthamoeba strains isolated from contact lens-wearing keratitis patients in Austria

Eighteen cases of Acanthamoeba-associated keratitis among contact lens wear ers seen at the Department of Ophthalmology, Karl-Franzens-University, Graz , Austria, between 1996 and 1999 are reviewed. The amoebae were proven to b e the causative agents in three patients. The aim of our study was to discr iminate between clinically relevant and nonrelevant isolates and to assess the relatedness of the isolates to published strains. Altogether, 20 strain s of free-living amoebae, including 15 Acanthamoeba strains, 3 Vahlkampfia strains, and 2 Hartmannella strains, were isolated from clinical specimens. The virulent Acanthamoeba strains were identified as A. polyphaga and two strains of A, hatchetti, To our knowledge this is the first determination o f keratitis-causing Acanthamoeba strains in Austria. Clinically relevant is olates differed markedly from nonrelevant isolates with respect to their ph ysiological properties. 18S ribosomal DNA sequence types were determined fo r the three physiologically most-divergent strains including one of the ker atitis-causing strains. This highly virulent strain exhibited sequence type T6, a sequence type not previously associated with keratitis, Sequence dat a indicate that Acanthamoeba strains causing keratitis as well as nonpathog enic strains of Acanthamoeba in Austria are most closely related to publish ed strains from other parts of the world. Moreover, the results of our stud y support the assumption that pathogenicity in Acanthamoeba is a distinct c apability of certain strains and not dependent on appropriate conditions fo r the establishment of an infection.