ABSTRACT
M. C. MECKES AND J. A. MACDONALD. 2003.
Aims: Current US regulations (40 CFR 503) for Class A biosolids (treated sewage sludge) requires use of
multiple-tube fermentation techniques for fecal coliform or multiple tube enrichment techniques for Salmonella
spp. followed by isolation and biochemical and serologic confirmation. The technical difficulties and the time
required to complete the procedure for enumeration of Salmonellae in biosolids and sludges has limited the use of
this assay. This study was conducted to determine if a commercially available molecular probe system could be used
to isolate and enumerate Salmonella spp. in biosolids or sludges in less time than cultural techniques with
biochemical confirmation.
Methods and Results: Several types of treated and untreated municipal sludges were assayed for Salmonellae
using a cultural technique with biochemical and serologic confirmation and a DNA probe diagnostic test kit. The
results indicate that the molecular probe and the conventional fermentation tube technique yielded equivalent
results. Interestingly, the probe technique yielded results within 52 h following initiation of sample analysis
compared with the conventional fermentation tube technique with confirmation which required approx. 120 h.
Conclusions: These results suggest that the molecular probe system used for this work may be used to determine
the presence or absence of Salmonella spp. in biosolids within a relatively short time frame.
Significance and Impact of the Study: The ease of using the DNA probe test kit, along with its ability to
produce results in less than half the time of conventional culture techniques, suggests that this assay is useful for
determining the presence or absence of Salmonellae in biosolids samples.
Keywords: biosolids, DNA, DNA hybridization, methods, molecular probes, Salmonella, sludge.