Green tree frogs : contamination of covered reservoirs in Northern Australia

A number of Queensland water authorities have recently reported the faecal indicator Escherichia coli, derived from unknown sources, in their reticulated drinking water supplies. The aim of this study was to determine whether the Australian green tree frog (Litoria caerulea) is a potential source of such E. coli, as well as microfungi, in municipal water service reservoirs in Queensland. Excreta of L. caerulea were collected from the internal structures ofa water reservoir and analysed for E. coli using the Most Probable Number (MPN) Colilert ® method. Excreta were examined microscopically for the presence of microfungal colonies and these were identified by their spores and reproductive structures. Escherichia coli were recorded from 100% of samples collected for E. coli analysis with some MPN g-1 as high as 2.89 x 108. All samples collected for microfungal analysis supported extensive sporulating microfungal colonies. We have demonstrated for the first time that excrement of the Australian green tree frog (L. caerulea) is an important potential source of both E. coli and microfungal contamination of reticulated municipal water supply systems in Queensland, Australia.