The Use of Molecular Methods for Detecting and Discriminating Salmonella Associated with Foods — A Review

Abstract

The genus Salmonella is composed of two species, Salmonella enterica and Salmonella bongori. Only S. enterica subsp. enterica is considered of human clinical significance and consists of 1478 serotypes. A large number of virulence genes and virulence-enhancing genes have been described for Salmonella. There are more than 30 Salmonella specific genes that have been used for the polymerase chain reaction to detect and characterize Salmonella. The sensitivity of detection of Salmonella from complex matrices such as food and feces by PCR is invariably enhanced using nonselective or selective enrichment, particularly if followed by immuno-magnetic separation in addition to coupling the PCR with ELISA formats. R-plasmids are considered to be the main factors responsible for the horizontal transfer of antibiotic resistance genes in Salmonella. A sizeable number of primer pairs are available for determining by the PCR the presence of many antibiotic resistance genes in Salmonella isolates that are not necessarily specific for Salmonella. The collective PCR detection of members of the genus Salmonella in foods and environmental samples has been achieved by amplification of invA gene sequences that are highly conserved among all Salmonella serotypes in addition to the amplification of his gene sequences also present throughout the genus Salmonella. Amplification of 16S rDNA sequences have also been found useful for genus specific detection of Salmonella. d-Tartrate (dT⁺) fermenting strains have been found to result in less severe gastrointestinal infections than d-tartrate-nonfermenting (dT^-) strains. Primers have therefore been developed for distinguishing between (dT⁺) and (dT^-) strains. Among the molecular techniques available for strain discrimination of Salmonella isolates, pulsed field gel electrophoresis, random amplified polymporphic DNA analysis, ribotyping, multilocus sequence typing, subtracted finger printing, and enterobacterial repetitive intergeneric consensus typing have been found useful. Multiplex PCR has been found effective for simultaneously detecting Salmonella and other pathogens in foods, particularly with real-time PCR.

Key Words:

• detection
• molecular typing
• PFGE
• RAPD
• review
• Salmonella
• serotyping