Zebrafish embryos as a model host for the real time analysis of<i>Salmonella typhimurium</i>infections

TLDR

Animal models are the gold standard for studying bacterial virulence, but their lack of real‑time analysis and reliance on invasive sampling limit their utility. The authors infected 28‑hour‑old zebrafish embryos with DsRed‑labelled Salmonella typhimurium and used multidimensional digital imaging microscopy to track bacterial location and fate over three days in a living vertebrate host. Low‑dose wild‑type S.

Abstract

Bacterial virulence is best studied in animal models. However, the lack of possibilities for real time analysis and the need for laborious and invasive sample analysis limit the use of experimental animals. In the present study 28 h-old zebrafish embryos were infected with DsRed-labelled cells of Salmonella typhimurium. Using multidimensional digital imaging microscopy we were able to determine the exact location and fate of these bacterial pathogens in a living vertebrate host during three days. A low dose of wild-type S. typhimurium resulted in a lethal infection with bacteria residing and multiplying both in macrophage-like cells and at the epithelium of blood vessels. Lipopolysaccharide (LPS) mutants of S. typhimurium, known to be attenuated in the murine model, proved to be non-pathogenic in the zebrafish embryos and were partially lysed in the bloodstream or degraded in macrophage-like cells. However, injection of LPS mutants in the yolk of the embryo resulted in uncontrolled bacterial proliferation. Heat-killed, wild-type bacteria were completely lysed extracellularly within minutes after injection, which shows that the blood of these zebrafish embryos does already contain lytic activity. In conclusion, the zebrafish embryo model allows for rapid, non-invasive and real time analysis of bacterial infections in a vertebrate host.