Adherence pili in avian strains of Escherichia coli: effect on pathogenicity.

Several pathogenic strains of Escherichia coli were isolated from chickens and turkeys with severe colisepticemia. Electron microscopic examination showed that all these strains had thin pili (fimbriae) when grown at 37 C but not at 18 C. These pili facilitated adherence of the bacteria to chick tracheal epithelial cells both in vitro and in vivo. The role of these pili in pathogenicity was examined by comparing chicks infected intratracheally with piliated bacteria and chicks infected with non-piliated bacteria. The presence of adherence pili on the infecting bacteria affected both the number of chicks that developed disease and the severity of the disease.