Heterogeneity in cyst morphology within isolates of Acanthamoeba from keratitis patients in Thailand

We isolated Acanthamoebae from the first two keratitis patients identified in Thailand in 1958 and 1990. The patients developed decreased vision, seve re photophobia, severe eye pain and foreign body sensation after minor corn eal trauma. The lesions included generalized superficial punctate keratitis , stromal corneal ulcer with keratic precipitate and uveitis in one case, a nd corneal ulcer with abscess in the other. Both cases were diagnosed by is olation of characteristic trophozoites and cysts of Acanthamoeba from corne al tissue by non-nutrient agar culture method. Based on cyst morphology, A. castellanii and A. polyphaga were detected in one case, and A. castellanii and A. triangularis in the other. Restriction fragment length polymorphism analysis of mitochondrial DNA (mt DNA-RFLP) revealed that each patient har boured a single parasite population. One shared mtDNA-RFLP with an authenti c strain of A. castellanii, and the other gave a new unique pattern. Thus s pecies identification of Acanthamoeba based on cyst morphology per st can b e arbitrary, and mtDNA-RFLP may be more appropriate for accurate species/st rain differentiation amongst morphologically heterogeneous populations of A canthamoebae.