A total of 100 poultry farms in northern and middle areas of Jordan were sampled to investigate the bacteria associated with airsacculitis in broiler chickens. Of 170 bacterial isolates, 88.2% were identified as Escherichia coli, 8.8% as Ornithobacterium rhinotracheale, and 3% as Bordetella avium. Fourteen serotypes of E. coli were identified among 66 typeable isolates and the remainder were untypeable. The most prevalent serotypes were O1, O8, and O78. The main serotype of O. rhinotracheale was serotype A. Experimental inoculation of O. rhinotracheale via intravenous, intratracheal, and intra-air sac routes resulted in growth retardation, thickening in the air sacs, arthritis, and liver necrosis. Reisolation of O. rhinotracheale from the air sacs, liver, trachea, heart, and spleen at day 7 postinoculation confirmed its role. In vitro susceptibility testing revealed that E. coli isolates were sensitive to gentamicin and colistin, O. rhinotracheale to tetracyline, and B. avium to most of the nine antibiotics examined.

Antibiotic sensitivity testing of E.coli isolates, showed that most isolates were sensitive 100% to colistin sulphate and kanamycin/cephlaxine in the first degree, also gave different results to other antibiotics. On the other hand, the isolates showed complete resistance 100% for Ampicillin, Gentamycin, Pencillin G, Tetracycline and Tylosin, in addition to appearance of 11 multiple resistance pattern. The results of determination of minimal inhibitory concentration (MIC) for E.coli showed the presence of variable minimal inhibitory concentration in relation to the serotypes of E.coli when used different antibiotics.