Salmonella Typhimurium discreet-invasion of the murine gut absorptive epithelium
Fig 5
Cooperative S.Tm invasion occurs frequently in epithelial cell lines, but not in the absorptive gut epithelium of mice.
(A-C) S.Tm Multiplicity of Infection (MOI) in the gut of (Sm-pretreated) orally infected mice. Inflammasome-deficient (Nlrc4-/-) mice were orally infected with S.Tmwt for 12h. (A) Representative stitched image of an entire cross-section of the infected murine cecum. Scale bar: 500μm. (B) Representative up-close micrograph of the infected cecum lumen and mucosa. Lu.—Lumen; Ep.—Epithelium; Cr.—Crypt. Scale bar: 20μm. (C) Microscopy-based quantification of the MOI in the infected mouse cecum. Bar correspond to mean +/- SD of replicate infections in four mice. (D-F) S.Tm co-invasion occurs rarely in the mouse gut. Inflammasome-deficient (Nlrc4-/-) mice were orally infected with a 1:1 mix of S.Tmwt/pssaG-mCherry and S.Tmwt/pssaG-GFP strains for 12h. (D) Representative micrographs of the cecal epithelium. Blow-up shows magnification of boxed region. Lu.—Lumen. White arrows indicate one-coloured invasion foci; arrow head labelled “co-inv” indicates a mixed invasion focus. Scale bar: 10μm. (E) Quantification of the distribution of bacterial numbers within S.Tm invasion foci. (F) Quantification of the frequency of single-colour and mixed colour invasion foci in vivo. Bars in E-F correspond to mean +/- SD of replicate infections in four mice (Ntot = 1055 invasion events analyzed). (G-J) Prevalent cooperative S.Tm invasion in epithelial cell lines, but not in the absorptive gut epithelium in vivo. (G-H) Infection of (G) HeLa and (H) m-ICc12 cells with a 1:1 mix of S.Tmwt/pssaG-mCherry and S.TmΔinvG/pssaG-GFP strains for 1h at MOI 80. Representative micrographs. Blow-ups show magnifications of boxed regions. Arrow heads labelled “coop” indicate cooperative invasion foci. Scale bar: 20μm. (I) Inflammasome-deficient (Nlrc4-/-) mice were orally infected with a 1:1 mix of S.Tmwt/pssaG-mCherry and S.TmΔinvG/pssaG-GFP strains for 12h. Representative micrographs of the cecal epithelium. Blow-up shows magnification of boxed region. Arrow points to a rare S.TmΔinvG/pssaG-GFP invasion focus. Scale bar: 20μm. (J) Quantification of the frequency of cooperative invasion foci in HeLa, m-ICc12 cells (infection parameters as in G-H) and the absorptive gut epithelium in vivo (infection parameters as in I). Data points correspond to mean +/- SD of three replicate infections in HeLa and m-ICc12 cells, and to mean +/- SD of five mice (Ntot = 578 in vivo invasion events analyzed), respectively.