Detection of Salmonella in Sludge Sediments

A total of 145 sewage sediments samples from municipal and industrial wastewater treatment plants were tested for the presence of Salmonella using horizontal and PCR-based methods. Samples were pre-enriched overnight in buffered peptone water (BPW) at 37°C followed by 3 h enrichment in BHI broth at 37oC. Obtained samples from BPW were selectively enriched in RVS broth (24 h, 42oC) and MKTTn (24 h at 37oC). Resulting cultures were plated onto XLD and BGA agar plates, incubated at 37oC for 24h. Presumptive Salmonella isolates were biochemically and serologically confirmed. As a comparison method, samples from BHI were lysed to break down the cell walls and release DNA and tested as described by the BAX Q7 Salmonella PCR Assay (Dupont). Among 145 samples derived from the 134 sludge sediments analyzed with horizontal and PCR-based methods, identical results were obtained for 136 samples (93,8% identity) of which 110 pairs of results were Salmonella negative, 26 samples were Salmonella positive for both analytical methods. Results obtained with traditional method were opposite to that obtained with PCR method only in nine samples. In conclusion, PCR method using Bax Q7® system should be further optimized for such unusual matrix as sludge sediments in order to eliminate false negative results.