Significance of Specific Bacterial Pathogens in the Assessment of Polluted Receiving Waters of Sydney, Australia

Abstract

The impact of primary sewage released from Sydney's ocean outfalls and chlorinated tertiary treated sewage effluent discharged into Sydney's main river system (Hawkesbury-Nepean) have been studied for faecal microorganisms over two years. Faecal indicator bacteria and a range of potential bacterial pathogens (Aeromonas spp., Campylobacters, Pseudomonas aeruginosa, Staphylococcus aureus and salmonellae) were also cultured. Diverting primary-treated sewage from cliff edge release to deepwater (80m) ocean release some 3 km offshore resulted in significant reductions in all bacterial groups examined, with spores of Clostridium perfringens (C.p) being the most sensitive indicator of water quality improvement. In contrast, contamination of inshore sediments has not markedly declined. Campylobacters were not isolated from effluents or seawater, and numbers of S. aureus and P. aeruginosa were very low if detected. Inland river waters were dominated by motile aeromonads, and along with C.p were the most resistant organisms to chlorination following tertiary sewage treatment. However, aeromonads appeared to grow throughout the river system. Campylobacters were associated with areas of agricultural input whereas salmonellae appeared to be associated with significant urban sewage input. Of the indicator bacteria, C.p correlated best with salmonellae, while viruses correlated poorly with the bacterial groups examined. Further work is required to identify possible sources of virulent aeromonads, Campylobacters and salmonellae.