PCR Assays Based on invA Gene Amplification are not Reliable for Salmonella Detection

Background: Salmonella surveillance relies on invA polymerase chain reaction (PCR) assays for the rapid detection of Salmonella; however, false-positive results have been reported using this method. Objectives: To evaluate the performance and specificity of the published and validated PCR protocols targeting invA gene for the detection of Salmonella. Methods: The performance and specificity of it different PCR primer sets were evaluated using Salmonella type strains and Citrobacter spp., Escherichia coli and Serratia spp. isolates recovered during a Salmonella surveillance program. Results: It was revealed that the published PCR protocols using validated primers targeting invA and 16S rRNA genes generated false-positive signals. Importantly, a protocol targeting the ttrA/C genes was able to discriminate Salmonella and non-Salmonella isolates. Conclusions: Detection of Salmonella spp. by means of invA PCR amplification is not reliable. In fact, false-positive results are commonly obtained from Citrobacter, E. coli and Serratia isolates. It is recommended to use other loci, such as ttrA/Cgenes, for the accurate and reliable detection of Salmonella.