Modulation of cross-protection factor(s) of avian Pasteurella multocida.

Cross-protection factor(s) (CPF) of Pasteurella multocida were maintained in vitro through at least 9 serial passages. Different growth media and temperatures enhanced or repressed the ability of P. multocida to produce CPF. Certain amino acids were innoculous to expression of CPF. B-vitamins enhanced CPF, whereas certain inorganic salts repressed CPF. The plasma of normal tuekeys contained a compound or compounds that were responsible for expression and maintenance of CPF.