Application of PFGE performed with XbaI to an epidemiological and phylogenetic study of Salmonella serotype typhimurium. Relations between genetic types and phage types.

PFGE performed with XbaI was evaluated and applied as a typing method in a series of 68 Salmonella serotype Typhimurium strains collected in a Spanish region throughout 1984-1994, and four reference strains. Using bands > 100 kb as a separation criterion, 26 pulsed-field profiles (PFPs) were defined, with a discrimination index of 0.87. The XbaI-profiles were grouped into three clusters and two additional branches in a dendrogram of similarity (significance level = 0.7). Strains belonging to PFP-X1 and PFP-X2 predominated (26.4% and 23.6%, respectively) and fell into the major cluster. The series had been previously analysed by phage typing and a three-way ribotyping procedure, and a certain degree of relation among the three methods was revealed, PFGE being the most discriminatory. Combining data from the three methods a further differentiation into 46 clonal lines was obtained, and four lines, at least, could be considered as endemic in the region under study. This procedure proved to be a powerful epidemiological tool for characterization of Typhimurium and in the investigation of outbreaks.