Phylogeny and timeline of outbreak-related S . Typhimurium 135@ isolates. Maximum likelihood tree of the S. Typhimurium 135@ isolates, based on SNPs identified by mapping to the reference chromosome for S. Typhimurium SL1344. Bootstrap values for each bipartition were 100%. Isolates are labelled by their STm number and an icon indicating the specimen type (according to the legend provided); black numbers next to branches indicate the number SNPs contributing to that branch. Red bar graph indicates the timing and size of the seven outbreaks. Red branches in the tree indicate the farm clone; dashed lines link each isolate to its time of isolation and outbreak membership.