With DNA from S. Enteritidis strains, the prot6E-specific, TET-labelled molecular beacons hybridise to their target amplicons and produce an orange fluorescent signal, whereas the fliC-specific, HEX-labelled molecular beacons remain dark. With DNA

from other Salmonella serotypes, no target amplicons are detected and both molecular beacons remain dark. The dashed line on the plots Selleckchem AZ 628 represents the normalised threshold for detection of fluorescence, the baseline above which fluorescence increases significantly on amplification and detection of the target sequence. In both the uniplex and double duplex assays, non-template controls were included to verify the absence of false-positive results. In all cases they exhibited undetectable amplification of the targets (CT >45). Selectivity of the real-time assay The selectivity and accuracy of the test is measured by calculating the values for specifiCity

and sensitivity. SpecifiCity is the probability that the PCR will be negative among specimens that should not possess the gene and is calculated using the formula: true negative/(true negative + false positive). Sensitivity shows the strength of the test in recognising what we are looking for, i.e., in correctly identifying the specific serotype. The formula used for estimation of sensitivity is: true positive/(true positive + false negative). For the reaction targeting the invA gene, all 44 Salmonella samples investigated were positive SBI-0206965 cost indicating a sensitivity of 100%. The specifiCity was also 100% since all non-Salmonella samples gave negative results, Calpain with undetectable fluorescence signals after 50 cycles. In the prot6E reaction all S. Enteritidis samples analysed were identified

correctly with positive PCR results and all non-Enteritidis samples were negative for this target. Thus, this reaction also had sensitivity and specifiCity of 100%. Similarly, in the assay for fliC detection, all S. Typhimurium samples tested were positive for the target. The assay’s sensitivity was 100%, matched by an equal specifiCity value as all non-Typhimurium samples tested gave negative PCR results. Discussion Traditional serotyping of S. enterica is based on the detection of certain antigens using microbiological techniques and culturing, which are time-consuming and laborious. This study exploits real-time PCR, molecular beacons and genetic variation between different serotypes to devise a quick, accurate and simple assay to reliably identify a bacterial sample as Salmonella enterica and further distinguish it as serotypes S. Typhimurium or S. Enteritidis, the two serovars most commonly associated with food-borne gastroenteritis. The assay described in this study can analyse a large number of samples very quickly, and can also identify as few as 10 copies of target DNA per reaction, potentially even in the presence of thousands of copies of other serotypes.