الفهرس 
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Abstract
Ornithobacterium rhinotracheale (ORT) is one of the accusative organisms that cause respiratory diseases of chickens. This disease results in severe issues of intensive poultry industry and its products. Therefore, isolation, identification, investigation on antibacterial sensitivity and multidrug resistance patterns of ORT isolates were the main aims of this study. This study also was aimed to determine antibacterial effect of some herbal extracts and their role in enhancing antibiotic effects against investigated ORT. The incidence values of ORT by cultural method were 20.0 and 3.0% from the tracheal samples of dead birds under and above 18day respectively with postmortem lesions of respiratory illness. Out of 23)11.5%) cultural positive samples, 15(65.21%) were found positive for the presence of 16S rRNA (625 bp) by PCR. The results of antibiotic sensitivity revealed that 66.6% of isolates were sensitive to amoxicillin, while 60.0 and 46.6% of isolates were sensitive to erythromycin and florfenicol, respectively. For difloxacine and doxycycline, the frequency of sensitive samples was 33.3 and 13.3%, respectively. The highest antimicrobial resistance of ORT isolates was seen against gentamycin and colistin (100%), followed by doxycycline (86.6%) and difloxacine (66.6%).
Ethanolic extract of some medicinal plants including Galic (Allium sativum) bulb, Eucalyptus globulus leaves and rosemary (Rosmarinus oficinalis) leaves were prepared. MIC of these plant extracts, selected antibiotics and a mixture of plant extracts and antibiotics was evaluated to enhance antibiotics against ORT in-fections. The MIC for the ethanolic extract of Eucalyptus against ORT particularly was found to be significantly active than garlic and rosemary. Results revealed synergistic effect appears in rosemary with amoxicillin by ratio (1:9), (2:8) and rosemary with erythromycin by ratio (1:9) while the synergistic effect of Eucalyptus and amoxicillin appears by ratio (1:9), (2:8) and Eucalyptus with florfenicol by ratio (1:9), (2:8). On the other hand the synergistic effect of garlic and amoxicillin was by ratio (1:9), (2:8) and (3:7) and garlic with florfenicol and erythromycin by was the ratio of (1:9), (2:8), (3:7).
In conclusion, it is very important to update the baseline resistance pattern data for this organism. The use of plant extracts may have the potential to enhance or replace antibiotics to control infections against ORT in poultry production.
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