The use of MAPLT and MLVA analyses of phenotypically closely related isolates of Salmonella enterica serovar Typhimurium

The resolving power of multiple-locus variable-number tandem repeat analysis (MLVA) was undertaken on 78 phenotypically closely related isolates of Salmonella enterica serovar Typhimurium that were previously analysed with multiple amplification of phage locus typing (MAPLT) and pulsed-field gel electrophoresis (PFGE). Isolates were tested with 10 primer sets targeting tandem repeat loci in the S. Typhimurium genome. A new primer set targeting the SB21ST64B locus was also assessed for MAPLT analysis. Both methods produced similar levels of discrimination between 41 non-DT 126 isolates while MLVA proved superior in separating the DT 126 isolates. Results showed that two loci, STTR5 and STTR6, provided the most variation in tandem repeat numbers between the 78 S. Typhimurium isolates with 11 alleles detected for each locus. Some isolates did not produce amplified product with PCR for various loci, providing another level for discrimination. The remaining MLVA loci provided less allelic variation, with 4 loci failing to provide any discrimination. There were a number of isolates that were shown to be unique by one method but were clustered by the other method. Combining the most variable regions of both MAPLT and MLVA into one assay may provide significant resolution of isolates with the minimal number of primers utilised.