The occurrence of Listeria spp. and Salmonella spp. in surface waters

Listeria ssp., mainly Listeria monocytogenes as well as Salmonella spp. are recognized as significant human pathogens. The purpose of this study was to examine the occurrence of Listeria spp. and Salmonella spp. in surface waters of Northern Greece and to investigate the correlation of these pathogens with the standard indicator bacteria. A total number of 128 water samples from four rivers and one lake were examined for the presence of Listeria, Salmonella, total coliforms, faecal coliforms and faecal streptococci. For isolating Listeria, 250 ml of water were filtered through 0.45 microns pore size membrane, that was transferred in 10 ml listeria enrichment broth and after incubation for 24 h at 30 degrees C, a second enrichment in FDA and Fraser broths was followed. After 24 hour incubation, an amount of 0.1 ml was streaked out onto listeria selective medium. The typical colonies were further biochemically and serologically examined. Salmonella spp. were isolated after preenrichment in BPW, enrichment in Rappaport-Vassiliadis and selenite cysteine broths and identified from BGD and SS agar plates by biochemistry and serology. Listeria monocytogenes was isolated from five (3.9%) and Salmonella spp. from eight (6.2%) samples. Mean log values of the standard indicator bacteria did not significantly differ between listeria and salmonella positive and negative samples.