Survival of pathogenic and faecal indicator bacteria in the bed and bank sediments of the Yarra River estuary, Australia

If faecal microorganisms survive for extended periods in river bed sediments, then this might be a critical source of faecal microorganisms in the water column of contaminated streams that is difficult to remediate. To determine the ability of bacteria to survive in a historically-contaminated urban stream, viable counts of faecal indicator bacteria and pathogens were conducted in the bed and bank sediments of the Yarra River estuary, Melbourne, Australia. In a first stage, core samples were collected at three locations along the Yarra River on a monthly basis and the viable counts of E. coli, the traditional faecal indicator bacteria, was monitored over time in the water column and the bed sediments. In a second stage, viable counts of E. coli and the bacterial pathogen, Campylobacter, were monitored over time at different depths in the cores that were incubated in the laboratory. In a third stage samples were collected at different location along the banks of the river and tested for E. coli and Campylobacter. Across all studies, the results show that E. coli and Campylobacter can survive in the bed and bank sediments of the Yarra River estuary. E. coli survival outside a warm blood animal host have already been widely established in the literature and raises concern, however the survival of Campylobacter outside of a host has always been considered highly unlikely and therefore is even more concerning, because it could cause significant health risks to users of the estuary if resuspended. Also this study has shown that the high salinity of the estuary had little effect on E. coli survival. The growth dynamics of both E. coli and Campylobacter are complex and depend on a number of parameters, so further work is required to determine what chemical and biological factors minimize this source of pathogenic bacteria in historically-contaminated stream sediments.