Uptake and excretion of Brucella abortus in tissues of the face fly (Musca autumnalis).

To determine their capacity to host Brucella abortus, face flies were examined 1 to 120 hours after feeding on broth containing bacteria and bovine erythrocytes. Brucella abortus was cultured in large numbers from whole flies for 12 hours after feeding, but not after 72 hours. Histologic analysis showed that brucellae were rapidly taken into the midgut, sequestered from erythrocytes, transiently stored, and shed in the feces; there was no evidence of bacterial replication within epithelial cells. Immunoperoxidase and immunogold techniques revealed that most brucellae in the gut were confined to the lumen by the peritrophic membrane, that brucellae were degraded in secondary lysosomes of midgut epithelial cells, and that intact brucellae passed into connective tissues surrounding the midgut. Bacterial excretion without midgut replication is consistent with transient, but not long-term, insect transmission in nature.