Acanthamoeba strains isolated from organs of freshwater fishes

Contrary to data on Acanthamoeba infections in humans, little is known abou t infections in fishes. The present study combines the description of strai ns isolated from fishes with presentation of an improved method for subgene ric classification. Acanthamoeba spp. were isolated aseptically from tissue s of 14 (1.7%) of 833 asymptomatic fishes collected in rivers and streams i n the Czech Republic. Acanthamoebae successfully cloned from 10 of the 14 i solated strains were examined here. Morphology of these isolates was evalua ted using light optics plus scanning and transmission electron microscopy. Cyst morphology, which varied extensively within and among clones, was most like morphological group II, but species-level classification was consider ed impossible. A distance analysis based on 442 bases in an 18S rDNA polyme rase chain reaction fragment of about 460 bp placed the isolates in a clade composed of sequence types T3, T4, and T11, the 3 subdivisions of morpholo gical group II. Fluorescent in situ hybridization (FISH) using oligonucleot ide probes indicated that all isolates belong to a single subdivision of gr oup II, the T4 sequence type. It has been concluded that the fish isolates are most closely related to strains commonly isolated from human infections , especially Acanthamoeba keratitis. The shorter diagnostic fragment sequen ces have proved nearly as useful as complete 18S rDNA sequences for identif ication of Acanthamoeba isolates.