Fig 1.

Cluster analysis of avian S. Typhimurium pulsed-field gel electrophoresis (PFGE) patterns generated with the restriction enzyme XbaI. Tiff images of S. Typhimurium PFGE patterns were compared using DNA pattern recognition software (BioNumerics; Applied Maths, Austin, TX). Levels of similarity were calculated using the band-based Dice similarity coefficient, and clustering of samples was performed using the unweighted-pair group method using average linkages (UPGMA). Six major PFGE clusters, A to F (>85% similarity), were identified among 162 avian S. Typhimurium isolates examined. Within PFGE clusters A, B, and D, additional PFGE subtypes, in which patterns differed by only 1 to 4 DNA fragments, were identified. The majority of songbird S. Typhimurium isolates produced PFGE A (subtypes 1 to 12) patterns with the restriction enzyme XbaI.