claved seawater, growth was always more gradual and never reached ... the Gulf of Mexico on the ocean side of Galveston. Island. .... E. coli rapidly died away in.
APPLIED AND ENVIRONMENTAL MICROBIOLOGY, July 1976, P. 114-120 Copyright ©D 1976 American Society for Microbiology
Vol. 32, No. 1 Printed in U.S.A.
Effect of Sediments on the Survival of Escherichia coli in Marine Waters CHARLES P. GERBA* AND JOHN S. McLEOD Department of Virology and Epidemiology, Baylor College of Medicine, Houston, Texas 77030 Received for publication 6 November 1975
Escherichia coli, a fecal coliform, was found to survive for longer periods of time in unsterile natural seawater when sediment material was present than in seawater alone, and at least on one occasion growth was observed to occur. This enteric bacterium was found to increase rapidly in number in autoclaved natural seawater and autoclaved sediment taken from areas receiving domestic wastes, even when the seawater had salinities as high as 34 g/kg. However, in autoclaved seawater, growth was always more gradual and never reached numbers as high as those observed when sediment was present. It was found that nutrients were easily eluted from the sediment after autoclaving or upon addition to artificial seawater, but little elution occurred during mixing of the sediments with unsterile natural seawater. The longer survival ofE. coli in the sediment is attributed to the greater content of organic matter present in the sediment than the seawater. These laboratory results, in part, could explain why on a volume basis larger numbers of coliforms and fecal coliforms were found in estuarine sediments than the overlaying water at field sites.
The presence of coliform organisms as an index of water pollution by domestic wastes has long been utilized in this country. The use of this group as an indicator of potential danger from bacterial pathogens in the same water depends on an understanding of their behavior in nature. There has been an increasing body of evidence that indicates that organisms of this group are capable of limited growth both in autoclaved polluted stream water (10, 11) and in chlorinated sewage effluents (17). Hendricks (8) demonstrated the ability of members of the Enterobacteriaceae, including several potentially pathogenic species, to utilize nutrients eluted from sediments obtained from a fresh water stream above and below where sewage was being discharged. In another study, Hendricks and Morrison (11) observed growth of fecal coliforms contained in dialysis bags in sewage-contaminated river water but not in unpolluted water. However, all of these studies were performed with autoclaved samples and excluded the effects of native microflora and other factors that might have been affected by autoclaving. These observations indicate the ability of fresh water aquatic systems to support and maintain enteric bacteria if the effect of native microflora is excluded. This problem has yet to be related to the marine environment, where conditions are thought to be far more detrimental to bacterial survival. In addition, it has not
been demonstrated what effect sediment from either fresh or marine waters has on the survival of fecal coliforms under unsterile conditions. This paper reports the results of a study on the effects of estuarine sediments on the survival of Escherichia coli in marine waters. MATERIALS AND METHODS Study sites. Estuary water and sediment were collected from several residential canal communities bordering Galveston Bay proper and West Bay. All these areas were known to be receiving domestic sewage pollution from septic tanks or outfalls. Water and sediment samples were also collected from the Gulf of Mexico on the ocean side of Galveston Island. This area is known to be free of sewage pollution. These sites were chosen because they represented a spectrum ranging from areas of high coliform counts to areas that were negative for coliform organisms. Table 1 is a record of the salinity, coliform, and fecal coliform counts observed in the water and sediment at each site during the study. Organism. A strain of E. coli (ATCC 15597), obtained from the American Type Culture Collection, was used in this study. Collection of water and sediment samples. Water samples were collected at the surface in sterile glass bottles. Sediment samples were collected with the aid of an Ekman dredge. All samples were kept cool in an ice chest until they were returned to the laboratory, where they were kept at 4 C until use. All samples were used within 24 h of collection. Survival studies. Water samples were placed in 250-ml Erlenmeyer flasks in 100-ml amounts. For
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TABLE 1. Salinity, coliform and fecal coliform values of collection sites Fecal coliformsa Salinity Coliformes Site no.
1 2 3 4 5 6 7
range
(g/kg)a 4-6 8-18 8-18 20
28 28-30 34
Water 540-35,000 1,300-35,000
240-35,000 79 17-33 8-240
