Experimental reproduction of airsacculitis and septicemia by aerosol exposure of 1-day-old chicks using Congo red-positive Escherichia coli.

To further demonstrate the association of phenotype and virulence of Congo red Escherichia coli (CREC), experiments were designed to reproduce airsacculitis and colisepticemia in 1-day-old chicks via aerosol exposure. In eight separate experiments in which a total of 462 chicks were exposed to CREC, the mortality rate was 4.11% and the morbidity rate was 13.4%, with both the dead and diseased chicks showing lesions of fibrinous airsacculitis, pericarditis, and perihepatitis. In contrast, when the corresponding non-CREC derivatives (the same E. coli strains, but not expressing the CR phenotype) were used as the aerosol inoculum in five additional experiments using 284 chicks, no chicks died and no lesions were observed. These results clearly show a strong correlation between the expression of the CR phenotype and virulence in avian E. coli.