The microbiome protects against septic hyperinflammation and bacterial proliferation in a zebrafish model of blood infection with Escherichia coli and mycobacteria

Frontiers in Immunology, vol. 17, pp. 1837804

Abstract

The microbiome is an important immune regulator, but the mechanisms by which commensal microbes shape systemic host defense during bloodstream infection remain poorly defined and commonly used pre-clinical models have practical, ethical and scientific limitations. Here, we establish a gnotobiotic zebrafish larval model to investigate microbiome-dependent protection against systemic blood infection by Escherichia coli (E. coli) bacteria, an important cause of early onset neonatal sepsis. We also use nontuberculous mycobacteria to infect zebrafish larvae to investigate the contribution of Toll-like receptor 2 (TLR2) in the defense responses. Germ-free (GF) and conventionalized (CONVD) larvae derived from the same clutches were systemically infected with E. coli , revealing that microbiome colonization significantly reduces early mortality. RNAseq revealed a conserved core immune activation program in both GF and CONVD larvae, but the absence of a microbiome was associated with a broader transcriptional response and stronger repression of metabolic pathways, suggesting that commensal microbes buffer infection-induced metabolic suppression. Extending this framework to nontuberculous mycobacteria, we performed systemic infections with fluorescent Mycobacterium marinum and M. avium in tlr2 wild-type and mutant larvae under GF and CONVD conditions. While survival was largely unchanged, imaging-based quantification demonstrated increased bacterial proliferation in tlr2 mutants and in GF larvae, with microbiome-mediated restriction of bacterial burden evident in wild-type but not tlr2 -deficient hosts. Together, these data show that microbiome colonization buffers septic outcomes by reshaping systemic inflammatory and metabolic programs and identify TLR2 as a key node linking microbial colonization to effective host defense during nontuberculous mycobacterial infection.

Authors 4

1. Li Liu Aachen Institute of Biology Leiden

   Leiden University

   Affiliation as printed

   Institute of Biology Leiden, Animal Science and Health, Leiden University

2. Bjørn E. V. Koch Aachen Institute of Biology Leiden

   Leiden University

   Affiliation as printed

   Institute of Biology Leiden, Animal Science and Health, Leiden University

3. Elke H. J. Krekels Aachen Leiden Academic Centre for Drug Research

   Leiden University · Certara (United States)

   Affiliation as printed

   Certara Inc

   Leiden Academic Centre for Drug Research, Leiden University

4. Herman P. Spaink Aachen Institute of Biology Leiden

   Leiden University

   Affiliation as printed

   Institute of Biology Leiden, Animal Science and Health, Leiden University