Infection studies conducted using mice or poultry have shown that inactivation of aroA in P. multocida strains X-73, P-1059, and 85020 [41,42], tonB, exbB, and exbD in strain PM25 [43], plpB in strain VP161 [44], and nanP and nanU in strain P-1059 [45] all resulted in reduced virulence. Here, NANP is linked to infection.