Abstract
The phospholipase D (PLD) gene (pld) has been deleted from the Corynebacterium pseudotuberculosis chromosome by using site-specific mutagenesis. Sheep infection trials indicate that the PLD-negative C. pseudotuberculosis strain (Toxminus) is incapable of inducing caseous lymphadentis (cheesy gland) even at doses two logs higher than that at which the wild-type strain produces the disease. This clearly establishes PLD as a major C. pseudotuberculosis virulence factor. Vaccination of sheep with live Toxminus C. pseudotuberculosis elicits strong humoral and cell-mediated immune responses and protects the animals from wild-type challenge.