We examined partial 18S
ribosomal DNA (Rns) sequences of Acanthamoeba isolates cultured in a study of microbial
keratitis in Hong Kong. Sequence differences were sufficient to distinguish closely related strains and were used to examine links between strains obtained from corneal scrape specimens,
contact lenses, lens cases, lens case solutions, and home water-supply faucets of patients with Acanthamoeba. We also looked for evidence of
mixed infections. Identification of Acanthamoeba Rns genotypes was based on sequences of approximately 113 bp within the genus-specific amplicon ASA.S1. This permitted genotype identification by using nonaxenic cultures. Of 13 specimens obtained from corneal scrapes,
contact lenses, lens cases, or lens case solutions, 12 were Rns genotype T4 and the remaining one was Rns genotype T3. The sequences of corneal scrape specimens of two patients also were the same as those obtained from their
contact lenses or lens case specimens. A possible triple-strain
infection was indicated by three different T4 sequences in cultures from one patient's
lenses. Although faucet water used by patients to clean their
lenses is a possible source of
infections, specimens isolated from the faucets at two
Acanthamoeba keratitis patients' homes differed from their corneal scrape or lens specimens. The overall results demonstrate the potential of this Rns region for tracking
Acanthamoeba keratitis strains in
infections and for distinguishing single-strain and closely related multiple-strain
infections even when other microorganisms might be present with the cultured specimens. They also confirm the predominance of Rns genotype T4 strains in
Acanthamoeba keratitis infections.