Bacteria communicate with one another and with their host using chemical signalling molecules. This phenomenon is generally described as quorum sensing. A set of primers for PCR detection of Salmonella spp. has been designed using as target the sdiA gene which encodes a signal receptor of the LuxR family. The PCR product (274 bp) was confirmed by sequencing. A number of 81 non-Salmonella strains (representing 24 different species) were tested and gave negative results, while a total of 101 different serotypes of Salmonella (155 strains) tested positive for the presence of the sdiA gene. The sensitivity and specificity of the sdiA-based PCR assay were also checked in artificially contaminated human faecal samples. In this study, we demonstrate that quorum sensing genes can be successfully exploited as diagnostic markers.

Aims:  The aim of this study was to develop a novel strategy that permits the independent amplification of internal amplification control (IAC) and target sequence using the same set of primers, to improve the sensitivity of diagnostic PCR assays. Methods and Results:  The method described here is a Salmonella specific PCR test targeting the quorum sensing gene sdiA. It is based on a large size difference between the IAC and the target and consequently on their different extension time. The results indicate the enhanced sensitivity of this test when compared with the competitive IAC strategy. This is demonstrated through parallel testing of artificially contaminated human faecal samples. Conclusions:  Utilizing this method, the concentration of the IAC, which often leads to false negative results if the target is present in extremely low concentration owing to competition, does not constitute a critical parameter for the detection limit of a PCR assay. Significance and Impact of the Study:  To our knowledge, this is the first report of using extension time as a critical parameter for the sensitivity of a PCR test. A different approach for the construction of an IAC, based on inverse PCR, has also been introduced.