Genotypic characterization of Acanthamoeba spp. causing ocular infections in Swedish patients: identification of the T15 genotype in a case of protracted keratitis.

The genus Acanthamoeba represents free-living amoebae typically widespread in soil and water. It consists of more than 20 known species representing 15 genotypes of different pathogenicity and virulence. The aim of the study was the genotypic characterization of Acanthamoeba spp. isolated from human keratitis cases in Sweden. Thirteen amoeba isolates obtained from contact lens users with suspected Acanthamoeba keratitis (AK) were subjected to polymerase chain reaction amplification and subsequent sequencing of the SSU rRNA gene fragment. Sequence analysis identified 4 different genotypes in the studied material. The majority of samples (92%) represented sequences of T3, T4 and T11, all belonging to a cluster of related genotypes frequently described in AK cases. Similar to other reports, genotype T4 was the most common finding in our material (77% of samples). Interestingly, an uncommon genotype, T15, mostly reported from environmental sources, was found in a sample from a patient suffering from a protracted keratitis.