Ingestion of Erwinia carotovora carotovora 15 ( Ecc15 ) induces dramatic morphological changes to the gut of Drosophila. (a) Quantitative measurements of the gut at different time points after infection reveal that Ecc15 induces a dramatic remodeling of the gut. The midgut lengths and widths, the total number of cells and the number of mitotic stem cells (phosphohistone H3 (PH3)-positive cells) along the midgut are shown. Measurements of colony-forming units (CFUs) per gut of Ecc15 at corresponding time points are also shown. (b) Representative images of guts dissected from wild-type (WT), unchallenged (UC) or Ecc15-infected flies stained with 4',6-diamidino-2-phenylindole (DAPI) and observed by light microscopy at ×10 original magnification. Gut length is decreased at 4 hours after infection, but returns to unchallenged levels by 48 hours. MT, Malpighian tubules; HG, hindgut. (c) Expression of green fluorescent protein (GFP) under the control of enteroblast (Su(H)GBE-Gal4; UAS-mcd8GFP) or intestinal stem cell (ISC) (delta-Gal4; UAS-nlsGFP) specific reporter genes was monitored following infection with Ecc15. Soon after infection (> 2 hours), expansion of Su(H)GBE-Gal4; UAS-mcd8GFP GFP signal was observed along the gut, reflecting the rapid differentiation of enteroblasts into larger enterocytes. The expansion of delta-Gal4; UAS-nlsGFP was observed only after 4 hours, indicative of ISC proliferation.