Abstract
Cloacal bursae from three-week-old gnotobiotic turkeys were examined by light and electron microscopy and bacteriologic techniques at 1, 2, 5, 8, 12, and 16 days after oral inoculation of highly virulent (group 1) and weakly virulent (group 2) Escherichia coli. In both groups a significant decrease in follicular volume and increase in interstitial volume were associated with infection. Follicular cortical, follicular medullary and total follicular transectional areas increased with time in inoculated and control turkeys. In group 1, granulocytic inflammation developed in bursae on day 1 and diminished by day 8 after inoculation. Microabscesses were present on days 5 and 8 after inoculation in less than 1 % of follicles. Bacteria were seen in few follicular medullae on days 5 and 8 after inoculation; bacteremia was detected on days 1, 2, and 5 after inoculation. In group 2, pyogranulomatous bursitis was first seen at five days after inoculation and became progressively more severe with time. Follicular alterations in group 2 included abscessation, lymphocyte necrosis, reticuloepithelial hyperplasia and perifollicular fibroplasia. Ultrastructurally, follicular pads had degenerate and necrotic epithelial cells, intercellular edema, and cystic spaces that contained acidic mucosubstances and laminar deposits of calcium salts. Bacteria were seen within necrotic centers of follicular abscesses, in phagosomes of macrophages and multinucleate giant cells and within extracellular spaces of follicular pads and follicular medullae from day 5 to day 16 after inoculation; no bacteremia was detected. We conclude that E. coli passes through the bursal follicle-associated epithelium and replicates within follicular medullae, that extensive follicular necrosis is associated with persistence of E. coli in follicular medullae, and that E. coli of low virulence may cause severe pyogranulomatous bursitis in young turkeys without causing the respiratory or systemic diseases which are commonly associated with organisms of high virulence.