Direct detection of enteropathogenic bacteria in estuarine water using nucleic acid probes

Direct detection and enumeration of pathogenic bacteria, rather than indicator organisms, in aquatic environments is desirable but hindered by the difficulties of culturing and identifying specific pathogens from these environments. We have developed a method for concentrating bacteria from water samples and extracting their DNA and RNA for use as targets for pathogen-specific gene probes. The method has been used to detect and enumerate Salmonella spp. in estuarine water samples. The probe binds Salmonella DNA quantitatively, making it possible to estimate relative amounts of target in each sample. Salmonella spp. were detected in samples which yielded no Salmonella spp. using culturing. Since the probe method does not require culturing the target organism, both culturable and non-culturable forms are detected. We have also used polymerase chain reaction to amplify a region of the enterotoxin gene in enterotoxigenic Escherichia coli and Vibrio cholerae (1tx and ctx, respectively). The amplified products are then identified with ctx and 1tx probes, making specific, highly sensitive detection possible.