Antimicrobial and immunological studies on Pasteurella multocida and Mannheimia haemolytica recovered from calves affected withrespiratory manifestations

Pneumonic pasteurellosis is the main cause of severe respiratory tract infections in calves and causing great economic losses. The objective of this research was to study the antimicrobial susceptibility of P. multocida and M. haemolytica and detection the effect of Lysozyme and Nitric oxide; as immune parameters, on most important bacteria causing pneumonic pasteurellosis in cattle calves. A total number of 406 deep nasal swabs and blood samples were collected from 406 bovine calves suffered from respiratory manifestations. Bacteriological examination revealed that the overall prevalence of both P. multocida and M. haemolytica was of 26.6%; 18.2% for P. multocida and 8.4%for M. haemolytica. P. multocida was singly isolated from 4.9% of cases. While it was mixed with S. aureus, E. coli, Streptococcus spp., both S. aureus and E. coli, both S. aureus and Streptococcus spp. and both E. coli and Streptococcus spp.with percentages of 4%, 1.2%, 2.2%, 1.7%, 3.2% and 1.0%, respectively. Meanwhile, M. haemolytica was isolated as a single isolate from 1.7% of cases while it was mixed with S. aureus, Streptococcus spp., both S. aureus and Streptococcus spp. and both E. coli and Streptococcus spp. with percentages of 2.7%, 1.2%, 2.5% and 0.2%, respectively. The in in-vitro sensitivity testing of all isolates showed high susceptibility to Fluoroquinolones and cephalosporins. On the other hand, high resistances were obtained against tetracyclines, penicillins and aminoglycosides. On the immunological level, the data of the existing research show that all respiratory affected calves record significant elevation of nitric oxide level in compare with normal control calves. However, all infected calves elucidate significant reduction of lysozyme activity.