Molecular characterization and ultrastructure of a new amoeba endoparasite belonging to the Stenotrophomonas maltophilia complex.

Naegleria and Acanthamoeba spp. were recovered from biofilm of a flushing cistern in a lavatory and both were found to be infected by rod-shaped bacteria enclosed within a vacuole. These intracellular bacteria behave like parasites, causing lysis of host amoebae. The bacteria proved unculturable on bacteriological media, and but could be maintained as endocytobionts within Acanthamoeba on agar plates. A marked differential host preference was observed in co-culture assays with various strains of amoebae. Molecular phylogenetic analyses performed on almost complete 16S rDNA sequences showed that the bacteria emerged as an atypical rapidly-evolving strain within the Stenotrophomonas maltophilia complex (Gamma-Proteobacteria, Xanthomonadales).