Evaluation of a DNA probe test kit for detection of Salmonellae in biosolids

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.