الفهرس 
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Abstract
Pasteurellosis is one of the most important economic diseases in ruminants, especially in cattle and buffaloes. It is caused by Pasteurella multocida and Mannheimia haemolytica. In the current study, a total number of 136 pneumonic and suddenly dead cattle and buffaloes of both sexes of different age groups, in winter and summer seasons were clinically examined. 128 nasal swabs and 41 blood samples were collected from 128 pneumonic cattle and buffaloes as well as 8 lung, 5 liver, 2 kidney, 4 heart, 4 spleen and 6 blood samples were collected from 8 suddenly dead cattle and buffaloes due to haemorrhagic septicemia. All samples were bacteriologically examined for isolation of P. multocida and M. haemolytica. There were 13 M. haemolytica and 8 P. multocida isolates recovered from the examined pneumonic cattle and buffaloes and 1 M. haemolytica and 4 P. multocida isolates recovered from suddenly dead cattle and buffaloes. Histopathological examination of different tissues collected from suddenly dead animals revealed sever pulmonary congestion and edema, diffuse vacuolization of myocytes with dispersion of myocardial fibers by serosanguinous edematous fluid, portal and sinusoidal congestion with periportal hemorrhages, centrilobular hepatocellular necrosis, fatty change of the midzonal hepatocytes, congestion of splenic red sinusoids and necrosis of the renal tubular epithelium with congestion of peritubular blood capillaries. The highest rate of infection was in males, in winter season and in (6-12 month) age group. The recovered isolates were examined for their antimicrobial sensitivity and it was found that P. multocida isolates were highly sensitive to levofloxacin, ciprofloxacin, norfloxacin, amikacin, enrofloxacin and sulphamethoxazole/trimethoprim with sensitivity rates 91.7%, 91.7%, 91.7%, 75%, 66.7% and 58.3%, respectively and M. haemolytica isolates were highly sensitive to levofloxacin, ciprofloxacin, norfloxacin, amikacin, sulphamethoxazole/ trimethoprim and enrofloxacin with sensitivity rates 100%, 92.8%, 92.8%, 85.7%, 78.6% and 57.1%, respectively. While the highest resistance rates in case of P. multocida were recorded against amoxicillin/clavulinic acid, ampicillin/sulbactam, oxytetracycline, streptomycin, cefotaxime and kanamycin with resistance rates 91.7%, 91.7%, 91.7%, 83.3%, 75% and 58.3%, respectively and in case of M. haemolytica the highest resistance rates were recorded against amoxicillin/clavulinic acid, ampicillin/sulbactam, oxytetracycline, streptomycin and cefotaxime with resistance rates 92.8%, 92.8%, 78.6%, 71.4% and 57.1%, respectively. All isolates were confirmed by PCR using kmt1 gene as universal primer for P. multocida isolates and rpt2 gene as universal primer for M. haemolytica isolates. Multiplex PCR was applied for capsular serogrouping of P. multocida isolates which detected capsular types A and D among the recovered isolates. Also, PCR was applied for detection of P. multocida virulence genes (omp87, toxA, ptfA and tbpA); omp87 gene was detected in 7 isolates, toxA gene was detected in 6 isolates, ptfA gene was detected in 5 isolates and tbpA gene was detected in only one isolate and M. haemolytica virulence genes (lktC and gcp) which detected in only 3 isolates.