Coliform bacteria in streambed sediments in a subtropical rainforest conservation reserve

Mean concentrations of coliform bacteria in streambed sediments in a subtropical rainforest conservation reserve in Queensland, Australia, undisturbed except by tourists walking, camping and swimming, were approximately 0.5×106 cfu/100 ml during the dry season and 1.2×106 cfu/100 ml during the wet season, with the difference significant at p<0.001. In general, total coliform concentrations in sediments were not significantly correlated with sampling site, rainfall, streamflow or visitor numbers on the sampling date. Concentrations in sediment were approximately 1000 times higher than in the overlying water column (95% c.i. 750–1500×). Eighteen individual bacterial species in the Enterobacteriaceae and Vibrionaceae were identified, including species of Klebsiella, Enterobacter, Escherichia, Acinetobacter, Citrobacter, Serratia, Providencia, Morganella, Plesiomonas and Aeromonas. Two of these, Plesiomonas shigelloides and Aeromonas hydrophila, are pathogenic to humans. P. shigelloides is a common cause of severe human diarrhoea in Asia. This is the first time it has been identified from natural surface waters in Australia.