[Salmonella: its incidence in waters of the Zaimán arroyo]

The present work is the initial stage of a project to determine the causes and degree of pollution of the Zaiman creek waters, which flow through wide suburban areas of Posadas, Argentina. The research was focused on the presence of Salmonella serotypes, pathogenic microorganisms probably responsible for most waterborne disease outbreaks. In addition, the N.M.P./100 ml (Most Probable Number) of total coliform organisms was determined in samples collected from points near cold storage plant and slaughterhouse, both to show the pollution effect of industrial discharges. So far, 35 sampling operations have been carried out in representative geographic points. The methodology for Salmonella consisted in applying concentration technics for waterborne pathogens, followed by an enrichment procedure performed by incubating samples in Dulcitol Selenite and Tetrathionate (Muller-Kauffman) broths at 41.5 degrees C during 25 hours. Typical, well-isolated Salmonella-like colonies were obtained by streaking duplicate plates of E.M.B. Agar (Eosin Methylene Blue), Brilliant Green Agar and Bismuth Sulphite Agar. Suspected colonies were classified by 10 biochemical reactions and further verified by serological identification, performed at the National Institute of Microbiology "Carlos Malbrán". The methodology followed for the determination of total coliforms was the one described in the American Water Standards. Salmonella serotypes were isolated in 46% of the examined samples. Isolation efficiency of culture media is shown. First isolations of Salmonella abaetetuba and S. saphra are reported. Most serotypes were isolated from sampling points down-stream from the industrial plant. Zaimán creek waters were classified as No 4 of W.H.O (World Health Organization) stream waters classification, except during heavy rain periods in which they ranked as No 3.