A comparison of two PCR-based typing methods with pulsed-field gel electrophoresis in Salmonella enterica serovar Enteritidis

Two novel molecular typing methods, multiple-locus variable-number tandem repeats (VNTR) analysis (MLVA) and multiple amplification of phage loci typing (MAPLT), were compared with pulsed-field gel electrophoresis (PFGE) for the discrimination of 128 Salmonella enterica serovar Enteritidis (S. Enteritidis) isolates. Selected epidemiologically unrelated isolates represented a cross-section of phage types routinely isolated in Australia and included 28 isolates that could not be assigned a phage type. Targeting 5 previously described loci, MLVA generated 61 different profiles with a Simpson index of diversity of DI=0.968. MLVA locus STTR-5 proved to be the most diverse with 11 different alleles detected with a Nei's diversity index value of D=0.769. Using 8 MAPLT primers previously developed for S. Typhimurium produced 36 different profiles with a DI value of 0.948. By contrast, PFGE only generated 13 different pulsed-field patterns, DI=0.873. Within each phage type there was variation in the extent to which either molecular method was able to discriminate the S. Enteritidis isolates. MAPLT provided more discrimination in terms of the number of profiles and DI value for phage type 1 and the untypable strains while MLVA was more discriminatory for phage types 14var and 26. There was a general lack of concordance of either molecular assay to phage type. These results suggest that both MAPLT and MLVA have excellent potential as tools for epidemiological studies of S. Enteritidis.