Tat-exported peptidoglycan amidase-dependent cell division contributes to Salmonella Typhimurium fitness in the inflamed gut
Fig 4
Possible link between host inflammation and AmiA- and AmiC-dependent competitive fitness.
(A and B) Streptomycin-treated C57BL/6 mice (n = 11) were infected for 6 days with 1:1 mixture (total 5×107 CFU intragastrically) of S. Tm invG ssaV and invG ssaV amiA amiC strains. (A) CIs of S. Tm loads in feces at 1, 3, and 6 dpi were determined. (B) Lipocalin-2 was monitored by ELISA. Data points represents geometric means ± standard deviations. (C) Streptomycin-treated C57BL/6 mice (n = 3 per group) were infected by gavage (5×107 CFU) for 3 days with GFP-expressing S. Tm invG ssaV or invG ssaV amiA amiC strains. Fecal pellets were collected, and then resuspended gently with PBS. The resulting S. Tm cells were observed by fluorescence microscopy. Representative fluorescence microscopy images of GFP-expressing S. Tm in the feces at 3 dpi (400x). Scale bar, 20 μm. (D) Quantitative analysis of the experiment. Data are shown as means ± standard deviations. ns, not significant; unpaired Student’s t-test. (E and F) Prior to treatment with streptomycin, C57BL/6 mice (n = 7) were exposed to 3.5% DSS ad libitum for 7 days. Subsequently, mice were treated with streptomycin, followed by mixed infection with invG ssaV and invG ssaV amiA amiC mutants via oral route. (E) CIs of S. Tm loads in feces or the cecum at 3 dpi were determined. (F) DSS-induced inflammation was verified by Lipocalin-2 ELISA. (G) Prior to treatment with streptomycin, C57BL/6 mice (n = 3) were exposed to 3.5% DSS ad libitum for 4 days, and treated with streptomycin, followed by infection by gavage (5×107 CFU) with GFP-expressing S. Tm invG ssaV amiA amiC mutant. Fecal pellets were collected, and then resuspended gently with PBS. The resulting cells were observed by fluorescence microscopy. Representative fluorescence microscopy images of GFP-expressing S. Tm in the feces at 3 dpi (400x). Arrow indicates chain form of S. Tm cells. Scale bar, 20 μm. For (A), (E) and (F), bar indicates median. ns, not significant; **P < 0.01; Mann-Whitney U test.