Growth phase-dependent phagocytosis of Pasteurella haemolytica by bovine pulmonary macrophages.

The ability of the bovine pulmonary macrophage (PM) to phagocytize Pasteurella haemolytica in its logarithmic and declining phases of growth was characterized. Pulmonary macrophages were harvested from bovine lungs before and after their in vivo exposure to P haemolytica. The PM from each lavage period phagocytized P haemolytica in the declining phase of growth. However, P haemolytica in the log phase of growth was not phagocytized by PM from any of the lavage periods. Instead, PM exposed to P haemolytica in the log phase of growth had altered cellular morphologic features and were cytolytic. Pasteurella haemolytica in the log phase also inhibited phagocytosis of Saccharomyces cerevisiae by PM. This inhibition of phagocytosis, as well as morphologic alterations, was evident in PM cultures exposed to P haemolytica for less than 1 minute.