Fig. 5

K. pneumoniae can infect zebrafish larvae by immersion and colonize its gastrointestinal tract. (A) Scheme of the gastrointestinal tract of a 5-dpf zebrafish larva, showing three arbitrarily defined zones (anterior, middle and posterior). (B) Semi-quantitative assessment of the intestinal colonization upon immersing zebrafish larvae in a suspension containing different K. pneumoniae strains or with E. coli DH5α. At the indicated time, larvae were anesthetized, observed under a fluorescence stereomicroscope, and the total intestinal colonization was scored in a scale from 1 to 9, following the criteria described in the Materials and Methods section. The data presented correspond to six replicates with a total of 75 larvae per bacterial strain. (C) Fluorescence microphotographs of zebrafish larvae representative of the data showed in (B). Bright field images of representative non-infected larvae at 48 and 96 h post-immersion are presented for more clarity. The larvae vasculature is shown in green, while infecting bacteria are shown in red. Scale bar, 500 μm. ****p < 0.0001.