CPB2 and necrotizing enterocolitis: NEC-associated isolates from sublineage VIf primarily carried pCW3 plasmids in either ~50-kb or ~70-kb sizes, encoding tetA(P) and tetB(P), cnaC and toxin gene cpb2, with the 50-kb plasmids missing ~20 genes due to transposases encoded by CPR_0630 on both flanks.