Epinephrine and norepinephrine increase the growth and expression of adhesins and proteases in Mannheimia haemolytica.

Mannheimia haemolytica (Mh) is an opportunistic pathogen that causes pneumonic infections in different ruminants. It is also part of the respiratory tract microbiome, but it descends into the lower respiratory tract under stress, causing shipping fever. The stress hormones epinephrine and norepinephrine have been suggested to induce Mh biofilm dispersion, but their roles in virulence have not been shown. In this study, the effects of these two hormones on Mh growth and on the expression of adhesins, proteases, and biofilm formation are evaluated. Physiological concentrations (1-5 ng/mL) of epinephrine and norepinephrine increase the growth of Mh and the expression of 42- and 75-kDa gelatin proteases, induce biofilm dispersion, and decrease biofilm protein and carbohydrate concentrations. At 50 or 500 ng/mL concentrations of epinephrine and norepinephrine, the expression of OmpA and OmpH adhesins and 42- and 100-kDa casein proteases increases. Bacterial adhesion to bovine monocytes or oral epithelial cells also increases, but antibodies against OmpH and OmpA diminish adhesion. Our results strongly suggest that epinephrine and norepinephrine modulate the expression of Mh virulence factors.