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Fig. 3
Localization of E. ictaluri in infected gnotobiotic zebrafish larvae.
At 3 days post-infection ( = 9 dpf), germ-free zebrafish larvae exposed at 6 dpf to E. ictaluri were analyzed by whole-mount immunofluorescence. Germ-free 9 dpf zebrafish larvae were used as control. A. Localization of E. ictaluri in infected larvae. E. ictaluri cells (red) were detected with a stereomicroscope by immunofluorescence using a polyclonal antibody recognizing Gram-negative bacteria, including E. ictaluri. White arrows pinpoint E. ictaluri main infection sites on zebrafish head and gut. Yellow arrows pinpoint non-specific labeling. B. Details of E. ictaluri insertion in larval intestinal tissue. Clusters of E. ictaluri cells (shown by large white arrows) were observed by confocal microscopy outside the gut lumen, surrounded by zebrafish intestinal cells (nuclei stained in blue). Left panel: 10× objective, transmitted light and red (bacteria) fluorescence overlay; central panel: 40× objective, transmitted light, dashed red lines indicate gut lumen boundaries; right panel: 40× objective, red (bacteria) and blue (nuclei) fluorescence overlay. C. 10× objective. Confocal fluorescence picture of larval head infected by E. ictaluri (red). Zebrafish cell nuclei are shown in blue (DAPI staining). D. Analysis of larval rostrum by fluorescence and Nomarski optics. White arrow shows a bacterial abscess within the oral cavity, whereas the yellow arrow pinpoints E. ictaluri clusters co-localized with external skin lesions. White bars = 50 μm.