Characterisation of some Ornithobacterium rhinotracheale strains and examination of their transmission via eggs

The biochemical characteristics and antibiotic susceptibility of 12 Ornitho bacterium rhinotracheale strains isolated from chickens and turkeys sufferi ng from respiratory clinical signs and the survival of some isolates on egg -shell and within chicken eggs during hatching were examined. All O. rhinot racheale strains showed typical biochemical characteristics. Among the 16 d rugs examined, penicillin G, ampicillin (MICs ranging from less than or equ al to 0.06 mug/ml to 1 mug/ml), ceftazidim (with MICs from less than or equ al to 0.06 mug/ml to 0.12 mug/ml), erythromycin, tylosin, tilmicosin (with some exceptions MICs ranged from less than or equal to 0.06 mug/ml to 1 mug /ml) and tiamulin (MICs varied from less than or equal to 0.06 mug/ml to 2 mug/ml) were the most effective. Lincomycin, oxytetracycline and enrofloxac in also gave good inhibitions, but with most strains in a higher concentrat ion (MICs ranged in most cases from 2 mug/ml to 8 mug/ml). The other antibi otics inhibited the growth of O. rhinotracheale only in very high concentra tions (colistin) or not at all (apramycin, spectinomycin, polymyxin B). At 37 degreesC, O. rhinotracheale did not survive on egg-shell for more than 2 4 hours, while upon inoculation into embryonated chicken eggs it killed emb ryos by the ninth day, and from the 14th day post-inoculation no O. rhinotr acheale could be cultured from the eggs at all. These results suggest that O. rhinotracheale is not transmitted via eggs during hatching.