We took the set of plasmids from Fig. 5 with at least 3 resistance genes (abbreviation 3G) and those with zero (abbrev. 0G). We defined “phylogenetic spread” of a plasmid as the median of the pairwise distances along a large subunit rRNA tree (incorporating branch lengths) between all pairs of genera in which the plasmid is detected, and calculated the 95% quantile of this distribution (red line). We then permuted the assignment of each plasmid to the classes 3G and 0G one million times (maintaining the class counts), each time calculating the difference in 95% quantiles for the two categories (3G and 0G). We show here the histogram of that statistic (i.e. the difference). This corresponds to a permutation test P value of 0.0024.