Fig. 2

Swim bladder infection in 4–5 dpf old larvae. Microinjection of W. chondrophila EBs directly into the lumen of the swim bladder of 4 dpf larvae. A drop of approx. 1 nl of the bacterial suspension can be seen hanging on the tip of the injection needle (arrow) inside the air filled lumen of the swim bladder (A). CLSM acquired 3D stack of the trunk region of a larva at 36 hpi, after IF staining with an anti-Waddlia antibody (red) and DAPI (blue). The swim bladder in the center of the image exhibits several bacterial inclusions (arrow heads) inside the epithelium (B). Histology on HE-stained sections of the swim bladder of a PBS injected control larva (C) with normal appearance and of an infected larva (D) showing clear pathological changes, including thickening of the epithelium (E) and infiltration of innate immune cells like macrophages and neutrophils (F). Scale bars (A–D) 100 μm, (E) 50 μm, and (F) 20 μm.