Iron-repressible Outer-membrane Proteins of Pasteurella haemolytica

The outer-membrane protein (OMP) profile of Pasteurella haemolytica grown under iron-replete and iron-restricted conditions was studied by polyacrylamide gel electrophoresis and immunoblotting. A serotype 1 isolate induced the synthesis of a new 77000 M r OMP in iron-restricted media while two other proteins of 100000 M r and 71000 M r were synthesized in increased amounts. None of these proteins were peptidoglycan-associated or heat-modifiable, and only the 100000 M r protein showed some degree of disulphide cross-linking. Kinetic analysis revealed that the iron-repressible proteins appeared in the outer membrane within 15 min of establishment of iron-restricted conditions. Analysis of P. haemolytica isolates representing serotypes 1 to 12 showed that iron-repressible OMPs of 77000 M r and 71000 M r could be induced in all 12 serotypes but that there was some variability in the expression of the 100000 M r protein. Immunoblotting of OMPs with convalescent sera from P. haemolytica-ifected calves indicated that antibodies directed against all three iron-repressible OMPs were present, suggesting that these proteins were expressed in vivo.