Determination of salmonellae from municipal wastewaters

This study compared the efficiency of culture methods for salmonellae detection in wastewaters collected from three Finnish municipal treatment plants and from one laboratory-scale plant. The performance of one-step enrichment in Preuss tetrathionate broth was better than that of two-step enrichment (buffered peptone water pre-enrichment (BPW) and selective enrichment in Rappaport-Vassiliadis (RV) medium. The best combinations for Salmonella isolation were xylose-lysine-deoxycholate (XLD) and Rambach (RB) agars after Preuss enrichment and did not differ when brilliant green-magnesium chloride (BM) or brilliant green phenol red (BP) agars were used. The two-step enrichment inhibited the growth of both salmonellae and interfering accompanying flora. Salmonella-positive plates were generally easier to read when inoculated from RV than from Preuss medium because of less growth of competing flora. XLD and BM agars supported growth of salmonellae and inhibited growth of competing flora better than BP and Rambach agars. XLD and BM agars gave the highest numbers of salmonellae isolations but XLD and Rambach agars gave the best differentiation. Salmonella levels were < 3- > 1100 MPN/100 mL.