Complex sentence: Diagnosis of the bacterium was traditionally based on clinical findings, culture and seriological testing, but false negatives have been a problem due to easy death of "P. multocida", and serology cannot differentiate between current infection and previous exposure.
Split into simpler sentences: Diagnosis of the bacterium was traditionally based on clinical findings, culture and seriological testing, but false negatives have been a problem due to easy death of "P. multocida". And serology cannot differentiate between current infection and previous exposure.