In vivo expression of iron regulated outer-membrane proteins in Pasteurella haemolytica-A1

Pasteurella haemolytica-A1 was grown in vitro under iron-rich conditions, iron-depleted conditions, and in vivo within a chamber implanted in the peritoneal cavity of a rabbit to determine if iron regulated outer-membrane proteins were expressed in vivo. The antigenicity of outer membrane (OM) proteins from bacteria grown under these conditions was assessed by immunoblotting with pooled serum from convalescent bovine calves experimentally infected with P. haemolytica-A1 and serum from the implanted rabbit. Pasteurella haemolytica-A1 grown under iron-depleted conditions showed three distinct OM protein bands (71, 77, and 100 kDa) that were present in much lesser amounts when the organism was grown under iron-rich conditions. These same three bands were evident in OM protein preparations from bacteria grown in vivo. Western blotting indicated that these protein bands were recognized immunologically by the convalescent bovine serum and by serum from the implanted rabbit, in cells grown under the iron-depleted conditions and in vivo, but not if the bacteria were grown under the in vitro iron-rich conditions.