RESUMO
A collection of 157 water samples from aquatic and marine environments and from potable and waste sources were analyzed to determine the total Listeria and L. Monocytogenes counts. For enumeration, both direct plate count and a selective enrichment MPN technique, followed by surface streaking onto selective agar medium were used. Listeria enrichment broth base provides with 3.75 [w/v] potassium thiocyanate, 0.01 g/l nalidixic acid and Listeria selective agar supplement with 0.01% [w/v] esculin and 0.05% [w/v] ferric citrate were used for the MPN and direct plate methods, respectively. Listeria species and L. monocytogenes occurred in 83-94% of fresh water samples and in 40-80% of marine water samples. Tap and bottled water samples were determined to be completely free of Listeria by both techniques. Less than one third of ground water samples examined harbored Listeria. They contained relatively low numbers of a few hundred Listeria/100 ml, which were mainly L. monocytogenes. All tested samples of raw and treated wastewater were positive for the presence of Listeria. The differences in counts may be attributed to the source of sample and the method of count. With regard to chlorinated effluent from wastewater treatment facilities, only 15% of tested samples were positive for Listeria for Listeria and L. monocytogenes