Ultrastructural Location of the Cross-Protection Factor on In Vivo and In Vitro Grown Pasteurella multocida

SUMMARY. Pasteurella multocida from infected turkey tissues expresses a unique immunogen called cross-protection factor (CPF) that induces immunity to challenge by both homologous and heterologous serotypes. In this study, we used a monoclonal antibody (AMP MAb) to CPF and protein A-colloidal gold (PACG) to locate CPF on P. multocida. After incubation with AMP MAb and PACG, CPF was detected at the bacterial surface and cell periphery of P. multocida in infected turkey liver and P. multocida isolated from infected turkey blood. CPF was not detected on P multocida incubated with control monoclonal antibody. Pasteurella multocida isolated from infected turkey blood and cultivated in the peptone-based medium did not express CPF consistently, and some cells contained more CPF than others. The location of CPF also varied, and CPF was detected both intracellular and extracellular on the cell surface. In the latter cells, CPF was heavily concentrated to a specific lateral site or detected sloughing from the cell surface. These results correlate with laboratory observations that CPF detected on P. multocida from infected turkey tissues, P multocida isolated from infected turkey blood, and P. multocida cultivated in peptone-based medium is associated with outer membrane fractions.