ABSTRACT
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.
Subject(s)
Salmonella/isolation & purification , Waste Disposal, Fluid , Water Supply , Agar/chemistry , Culture Media/chemistry , Environmental Monitoring/methods , Indicators and Reagents/chemistry , Population Dynamics , Sensitivity and Specificity , Tetrathionic Acid/chemistry , Water Pollution/analysis , Water PurificationABSTRACT
Cattle and other animals infected by Salmonella can emit high numbers of these bacteria. To determine an effective means for reducing this bacterial group in animal slurry, samples were subjected to aeration in laboratory experiments and in farm-scale slurry tanks. A clear reduction in Salmonella levels was found in laboratory experiments at temperatures from 4 to 40 degrees C. Aeration in farm-scale slurry tanks increased the temperature above the ambient temperatures (often less than 0 degrees C) to maxima ranging between 19 and 40 degrees C. Farm-scale aeration results in similar reductions in Salmonella as those achieved in laboratory experiments. Thus, reductions, ranging from greater than 99% of the initial number to no detectable Salmonella, could be reached after 2-5 weeks using aeration processes with cattle slurries contaminated by Salm. infantis or pig slurry contaminated by Salm. typhimurium. These results suggest that farmers can control the spread of Salmonella from slurry to agricultural fields. The reduction mechanisms remain unknown, though the increase in pH (to 7 x 6-9 x 0) found in slurries after aeration might exert a decreasing effect on these bacteria.
