Potentially pathogenic Acanthamoeba in swimming pools: a survey in the southern Brazilian city of Porto Alegre

Between May 2006 and March 2007, 65 water samples were collected from both heated and unheated swimming pools in the city of Porto Alegre, the capital of the Brazilian state of Rio Grande do Sul. The aim was to explore the problem posed by, and the pathogenic potential of, Acanthamoeba in the pools. Free-living amoebae in the samples were isolated by culture with Escherichia coli and identified from trophozoite and cyst morphology and the results of a PCR with Acanthamoeba-specific oligonucleotide primers. Potential pathogenicity was assessed in osmotolerance and thermotolerance assays. Thirteen (20%) of the water samples investigated were found positive for free-living amoebae, all identified as belonging to morphological groups II (nine isolates) or III (four isolates) of the genus Acanthamoeba. All 13 isolates were found positive in the Acanthamoeba-specific PCR, and the results of the tolerance assays indicated that five (38%) of the isolates should be considered potentially pathogenic. The results of this first study on the occurrence and distribution of Acanthamoeba in the water of swimming pools in Porto Alegre confirm the presence of potentially pathogenic types that may present a risk to human health.