Use of hybridization assay and direct immuno assay for detection of Salmonella spp. in surface waters and a comparison with conventional culture procedure.

Hybridization assay and direct immunoassay for detecting Salmonella in contaminated surface waters have been compared with the conventional culture procedure. The 67 samples examined were taken from different rivers in the provinces of Catania and Ragusa. By culture method, Salmonella was isolated in 23 samples (34%), while direct immunoassay revealed the presence of Salmonella in 58 samples (87%) and the hybridization method identified Salmonella in 20 samples (30%). On the basis of the results obtained, the direct immunoassay method proved to be inaccurate for the high number of false positives revealed. The DNA probe test gave almost identical results to those obtained with the culture method, with notably shorter execution times than the latter. This test proved to be both sensitive and specific and could be used for the direct demonstration of Salmonella in surface waters where it is easier to find bacteria under stress from the environmental conditions, in waters where isolation is difficult, and in all those environmental control conditions which do not require isolation and the serological typing of the strains of Salmonella.