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Patterns of island acquisition (PIA) among the strains. PIA 1, islands found in all clusters; PIA 2, islands found in cluster 1 (clades a/d and e/f), 2 (clade b), and 3 (clade c); PIA 3, islands specific to cluster 1; PIA 4, islands specific to cluster 2; PIA 5, islands specific to cluster 3; PIA 6, islands specific to cluster 4 (clade e’); PIA 7 is similar to PIA 1 but it is less represented in clusters 2, 3, and 4; PIA 8 is absent in cluster 1; PIA 9 is absent in clusters 1 and 2.
