Constitutive expression of bvgR-repressed factors is not detrimental to the Bordetella bronchiseptica-host interaction.

Bordetella bronchiseptica infection requires the activation of virulence genes by the two-component BvgAS regulatory system, which also activates bvgR, a repressor of another set of genes called avirulence genes. Whether or not BvgR-repressed genes play a role in pathogenesis is poorly understood. To evaluate their possible contribution to the bacteria-host interaction we constructed a B. bronchiseptica bvgR insertional mutant (BbBvgR mutant). As expected, this mutant simultaneously expressed virulence and avirulence markers. In vitro experiments demonstrated that, although the BbBvgR mutant expressed avirulence factors during its virulent state, the bacteria adhered to and survived within human epithelial cells as efficiently as the wild-type strain. The mutant was not impaired for colonization of the respiratory tract in vivo, as it was effectively cleared from lungs during the same time period as the wild-type strain.