[Various Salmonella serotypes isolated at a sewage purification plant in a large city over a one-year period].

The paper offers the results of a one-year-survey of Salmonella-serotypes in a municipal sewage-purification plant with a capacity of roughly 70,000 m3 per day. Findings of a quantitative study had shown Salmonella-maxima in the activated-sludge-basin. This suggested specialized Salmonella-serotypes, resident in this part of the plant as a possible explanation which was to be verified by this study. On ten days samples were taken from the inlet, and the outlet of the primary-sedimentation-tank, the outlet of the activated-sludge-basin and the effluent of the final sedimentation-basin. A combination of membrane-filtration and MPN-Method with a fifefold enrichment in 2.5% tetrathionate was applied for salmonella isolation. Plating was done on malachit-green-chinablue-lactose-agar followed by serological typing. 1,587 strains representing 38 different serotypes (Table 1) were identified with S. typhi-murium (Fig. 1) accounting for 36% of the isolations followed by S. bovis-morbificans, S. hadar (Fig. 2) and S. panama. None of the serotypes found showed a preference of a special sampling point. The qualitative and quantitative distribution of Salmonella in the plant seems to depend on the Salmonella contents of the entering waste water mainly. The greatest variety of Salmonella-serotypes was located in the activated-sludge-basin (Table 2) where oxygen-enrichment seems to result in the best ecological conditions for Salmonella survival. 3.3% of 722 strains examined did not produce hydrogen-sulphide (Table 3) and some showed damaged flagella-antigens. As a possible explanation toxic influences in the sewage are discussed. The epidemiological links between findings of Salmonella in sewage and in man of the same area are established and results differing in some aspects explained by the high rate of unknown infections. The existence of an autochthonous Salmonella-population in the sewage plant could not be proved.