Studies on the pathogenesis of Escherichia coli in the bursa of Fabricius (cloacal bursa) of the turkey.

Turkey poults were inoculated with avirulent or virulent strains of Escherichia coli by direct application to anal lips and were killed at postinoculation hours (PIH) 0.1, 2, 5, 10, 24, 48, 72, and 96. Bursae of Fabricius (cloacal bursae) were collected, cultured, and examined by light, fluorescent, and electron microscopy. The virulent strain of E coli was not recovered from the bursae after PIH 24, although the avirulent strain was recovered up to PIH 96. The E coli strains neither localized at nor associated with the bursal fold epithelium, passed through the follicular pad epithelium, nor caused cytopathologic changes in the lymphoid follicle. A mild catarrhal bursitis was observed at PIH 48 with the avirulent strain of E coli.