RESULTS
MMSDML
Table 1 shows the results of DNA hybridization assays
which were conducted on the heat treated/dried and
anaerobically digested biosolids. The most probable number
(MPN) of Salmonella spp. observed was calculated based
upon results from individual assays conducted on a single
dilution series of five culture tubes for a given mass of
sample (wet weight). The MPN of Salmonella spp. on a dry
weight basis was then determined by dividing the wet
weight MPN by the decimal fraction of the percent solids
for a given sample. None of the heat treated/dried biosolid
samples showed a positive response to the assay. Consequently,
the reported MPN results indicate the limit of
detection. Assays conducted on duplicate samples yielded
equivalent results (no positive responses). Samples spiked
with Salmonellae did yield positive results to the DNA
hybridization assay. As positive results were observed in
single culture tubes from these samples, densities could not
be determined. Confirmation of the presence of Salmonellae
was verified by recovery on selective media and subsequent
biochemical tests.
Samples of filter cake obtained following anaerobic
digestion were also tested for Salmonellae using the DNA
hybridization assay. Both of these samples yielded positive
results. This shows that DNA hybridization can be used
successfully to detect and quantify Salmonellae in such
samples. Again, confirmation of the presence of Salmonellae
was verified by recovery on selective media and subsequent
biochemical tests. All control samples responded as expected
with both Salmonellae cultures yielding positive results and
the P. mirabilis and E. coli cultures yielding negative results.
Recovery of Salmonella from spiked samples of heat treated