Use of Quorum Sensing Gene SdiA as a Molecular Marker for Salmonella Diagnosis

The alterations in cell density of the bacteria as a result of the gene expression mechanism is called quorum sensing and these changes in Salmonella has been an essential issue for a long time. The quorum sensing gene (sdiA) found in Salmonella spp. is an important regulatory gene for Salmonella survival, colonization and communication with other bacteria and hosts. Salmonella live in the human intestine, which harbors a great density and variety of bacterial cells, in addition to the other flora exist in the colon and all of them communicate amongst themselves and with the host itself to make a change for adaptive processes, such as antibiotic production, invasion of host cells and biofilm formation . Twenty-eight local Egyptian Salmonella isolates from different localities and different sources in Egypt such as, human stool, Egyptian cattle egrets and storks and grilled chicken from electric grills, were tested for the presence of sdiA gene by using PCR and compared with four non-Salmonella local isolates. All Salmonella isolates were PCR-positive for the sdiA gene (274-bp product). All non-Salmonella isolates were PCR-negative for the sdiA gene. Sequencing of sdiA gene revealed thet there were more than 99 % similarity to sdiA gene sequences existing in the GenBank database of different serotypes of Salmonella enterica strains. Therefore, it can be suggested that the SdiA gene is conserved among Salmonella enterica strains regardless of their serotypes. This work provide evidence that the sdiA gene is necessary for Salmonella virulence and the (sdiA) PCR assay is a unique, highly specific molecular marker for the diagnosis and detection of Salmonella.