Vermamoeba vermiformis does not propagate Legionella pneumophila subsp. pascullei in a simulated laboratory dental-unit waterline system

This study investigated whether Vermamoeba vermiformis and Legionella spp., co-habited within an established, mature biofilm of a simulated laboratory dental-unit waterline (sDUWL) and if this amoebic vector supported the life cycle of Legionella pneumophila. Trophozoites of V. vermiformis, isolated in a previous study, were cultured on a natural mixed biofilm bacterial culture and a pure culture of an avirulent, L. pneumophila (non-Sgp1strain ST707) as food sources. Vermamoeba did not show a preference for L. pneumophila. Legionella species were isolated from the sDUWL discharge water and identified by DNA profiling using 16s bacterial rDNA primers as L. pneumophila subsp. pascullei strain U8W. Electron microscopy was performed to establish whether V. vermiformis was acting as a carrier, whilst within the biofilm, for Legionella species isolated from the sDUWL water. Ultrastructure failed to demonstrate vast numbers of any bacteria within the cytoplasm of V. vermiformis that emerged from the same heterogeneous biofilm organisms. These results were taken to indicate that Vermamoeba was unable to propagate either of the Legionella strains studied.