Pseudomonas aeruginosa infection of zebrafish involves both host and pathogen determinants

Zebrafish (Danio rerio) have a number of strengths as a host model for infection, including genetic tractability, a vertebrate immune system similar to mammals, ease and scale of laboratory handling allowing analysis with reasonable throughput, and transparency, which facilitates visualization of the infection. With these advantages in mind, we examined whether zebrafish could be used to study Pseudomonas aeruginosa pathogenesis and found that infection of zebrafish embryos with live P. aeruginosa (PA14 or PAO1) by microinjection results in embryonic death, unlike E. coli or heat-killed P. aeruginosa, which have no effect. Similar to studies in mice, P. aeruginosa mutants deficient in type three secretion (pscD) or quorum sensing (lasR and mvfR) are attenuated in zebrafish embryos infected 50 hours post-fertilization (hpf), a developmental stage where both macrophages and neutrophils are present. In contrast, embryos infected 28 hpf, when only macrophages are initially present, succumb to lethal challenge with far fewer P. aeruginosa cells than embryos infected 50 hpf, are susceptible to infection with lasR and pscD deletion mutants, but are moderately resistant to infection with an mvfR mutant. Finally, we show that we can control the outcome of infection through the use of morpholinos, which allowed us to shift immune cell numbers, or small molecules (antibiotics), which rescue embryos from lethal challenge. Thus, zebrafish are a novel host model that is well suited for studying the interactions among individual pathogenic functions of P. aeruginosa, the role of individual components of host immune defense, and small molecule modulators of infection.