PURPOSE. This work was intended to test the classification of
Acanthamoeba into genotypes based on nuclear ribosomal
RNA gene (18S rDNA, Rns) sequences. Nearly all Acanthamoeba
keratitis (AK) isolates are genotype RnsT4. This
marked phylogenetic localization is presumably either due to
an innate potential for pathogenicity or to a peculiarity of the
gene sequences used. To differentiate between these possibilities,
relationships among isolates have been reexamined, using
a second gene.
METHODS. Phylogenetic relationships among isolates of Acanthamoeba
were studied, using sequences of the mitochondrial
small subunit ribosomal RNA gene (16S rDNA; rns). Genotypes
based on complete sequences of approximately 1540 bp were
determined for 68 strains, by using multiple phylogenetic analyses.
RESULTS. Each strain’s mitochondria contained a single intronfree
rns sequence (allele). The 68 strains had 35 different
sequences. Twenty-eight strains had unique sequences, and 40
strains each shared one of the seven remaining sequences.
Eleven mitochondrial rns genotypes corresponding to 11 of 12
previously described nuclear Rns genotypes were identified.
Genotype rnsT4 was subdivided into eight distinct clades, with
seven including Acanthamoeba keratitis (AK) isolates.
CONCLUSIONS. The phylogenetic clustering of AK isolates was
confirmed and thus is not specific to the nuclear gene. Rns and
rns sequences are both suitable for genotyping of Acanthamoeba.
However, the mitochondrial sequences are shorter
and more consistent in length, have a higher percentage of
alignable bases for sequence comparisons, and have none of
the complications caused by multiple alleles or introns, which
are occasionally found in Rns. In addition, the more common
occurrence of strains with identical rns sequences simplifies
identification and clustering of isolates. (Invest Ophthalmol
Vis Sci. 2003;44:1142–1149) DOI:10.1167/iovs.02-0485 |
