Evaluation and comparison of molecular techniques for epidemiological typing of Salmonella enterica subsp. enterica serovar Dublin

A total of 28 unrelated isolates of the Salmonella enterica subsp. enterica serovar Dublin collected during 13-year-period as well as four samples of the S. Dublin live vaccine strain Bovisaloral and its prototype strain S. Dublin 442/039 were investigated by different molecular typing methods for the following reasons: a) to find the most discriminatory method for the epidemiological typing of isolates belonging to this Salmonella serovar and b) to evaluate these methods for their capacity to discriminate between the live vaccine strain Bovisaloral, its prototype strain S. Dublin 442/039 and field isolates of the serovar Dublin. Five different plasmid profiles were observed; a virulence plasmid of 76 kbp as identified by hybridization with a spvB/spvC gene probe was present in all isolates. The detection of 16S rRNA genes and IS200 elements proved to be unsuitable for the epidemiological typing of S. Dublin; only one hybridization pattern could be observed with each of these methods. The results obtained from macrorestriction analysis strongly depended on the choice of the restriction enzyme. While the enzyme NotI yielded the lowest discriminatory index among all enzymes tested, it was the only enzyme that allowed discrimination between the Bovisaloral vaccine strain and its prototype strain. In contrast to the enzymes XbaI- and SpeI which only differentiated among the S. Dublin field isolates, the enzymes XhoI as well as AvrII also produced restriction fragment patterns of the Bovisaloral strain and of its prototype strain that were not shared by any of the S. Dublin field isolates. Macrorestriction analysis proved to be the most discriminatory method not only for the epidemiological typing of S. Dublin field isolates; it also proved to be suitable for the identification of the S. Dublin live vaccine strain Bovisaloral.