Live cell imaging of Salmonella Typhimurium interaction with zebrafish larvae after injection and immersion delivery methods
Surrogate host models have been employed to study bacterial virulence mechanisms of important human pathogens. Particularly, zebrafish (Danio rerio) has been used to determine the role of vertebrate innate immunity during bacterial infections. The easy-to-obtain large number of embryos and optical transparency of larvae allow live cell imaging of the infection progress and the major cellular types of the innate immune system that develop during the first days of embryogenesis. In zebrafish model, microinjecting bacteria into embryos and/or larvae can cause infection. Alternatively, an infection can be generated by static immersion of larvae on a microbial suspension. Both methods differ in the mode and time of infection, inoculum size and host response. In this work, we compare the in vivo immune response induced by Salmonella enterica serovar Typhimurium (S. Typhimurium) inoculated by immersion and microinjection in zebrafish larvae. To this end, an immersion protocol using transgenic zebrafish larvae was developed for in vivo monitoring of GFP-tagged S. Typhimurium infection progress and immune response during 72 h. The infection progress was compared to that of zebrafish larvae inoculated by microinjection. Our results in zebrafish corroborate previous Salmonella virulence studies in murine models and reveal that host-pathogen interaction not only depends on the virulence of the strain, but also on the inoculation method and host conditions.