The bacterial flora of the Pacific oyster Crassostrea gigas, the sea mussel Perna viridis and the arkshell clam Scapharca cornea differed considerably from that of seawater in both numbers and generic composition. The numbers of heterotrophic bacteria in the bivalve shellfish, including the anaerobes and spore-forming bacteria, were greater than that in the surrounding water. Pseudomonas spp. were the dominant organisms, comprising over one third of the 321 strains characterized after isolation from the bivalves and seawater. Other bacteria isolated from the shellfish included Vibrio, Acinetobacter, and Aeromonas spp., whereas the seawater flora consisted mainly of coliform organisms, coryneform bacteria and Flavobacterium/Cytophaga spp. Bacteria associated with the deposit-feeding clams were higher in density and more distinct in generic composition as compared with those in the suspension-feeding oysters and mussels. Over 90% of the coliform and heterotrophic bacteria in oysters were found in organs associated with the digestive tract. Coliforms were mainly found in the stomach while heterotrophs were present in both stomach and the lower intestine. The results suggest that the stomach flora of oysters are mainly derived from the external environment and, through a process of selection and multiplication, that it may be gradually replaced by a more indigenous population which dominates the lower digestive tract.
An animal model was used to determine the potential for causing wound infections of bacteria isolated from marine recreational beaches in Hong Kong. Water samples were characterized physically, chemically and bacteriologically and used to inoculate artificially-induced wounds in rats. Morbidity and mortality correlated significantly (P < 0.01) with MacConkey plate counts and faecal coliform counts (membrane filtration) and inversely with salinity of the water. The majority of deaths were due to infection caused by marine and estuarine bacteria rather then enteric organisms. A total of 318 bacterial strains was isolated from the wounds and blood of animals inoculated with seawater, of which 242 were marine/estuarine (predominantly Vibrio spp., Aeromonas hydrophila and Pseudomonas putrefaciens) and 40 were enterobacteria. The virulence of the animal strains were comparable with those from clinical sources.
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.
Two prospective studies on the occurrence of human viruses in samples of coastal & river origin have been undertaken since September 1989. Viruses were detected using concentration methods & cell culture techniques. Water samples (100L) were reduced to 1L using hollow fibre ultrafiltration and then treated with PEG. Sewage and sediment samples were treated with PEG only. Over a two year period, viruses were detected in 24/202 (12%) of water samples and 29/60 effluents from the river system. Coastal waters have been contaminated by cliff edge discharge of sewage for at least the last 70 years. Recently, deepwater ocean outfalls have been installed to discharge effluent some 3 km away from the coast. Prior to the installation of deepwater ocean outfalls viruses were detected in 28% of water samples compared to 9% post installation. In sediment samples viruses were isolated in 87/260 (34%) samples, the discharge via the new outfalls having no effect on the isolation rate. The data points to long term survival of viruses sediments and/or contamination from other sources such as storm water discharge: 10-25% of storm water drains were also found to be positive for viruses. The viruses isolated were enteroviruses, adenoviruses & reoviruses. Although viruses were consistently isolated with some seasonal trends, comparisons between the detection of viruses in clinical and environmental samples over this two year period were inconclusive.
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