FIG 5.

Precolonizing aerobic and anaerobic bacteria facilitate B. thetaiotaomicron (Bt) establishment in germfree mice. (A) E. coli WT and hemA mutant strains (10⁸ CFU) were each orally administered to germfree BALB/c mice. Sixteen hours later (T₀), 2 × 10³ CFU of B. thetaiotaomicron were administered to the two groups of animals precolonized with E. coli and to a group of naive mice. All mouse groups received the B. thetaiotaomicron doses at the same time and from the same bacterial preparation. Fecal samples were taken at 4-h intervals for 28 h for CFU determinations. E. coli hemA CFU were determined on LB plates containing δ-aminolevulinic acid (200 μM) incubated aerobically. (Top) E. coli (Ec) (CFU per gram feces); (bottom) B. thetaiotaomicron (CFU per gram of feces). Red, mice colonized with B. thetaiotaomicron alone; black, mice colonized with E. coli WT and then B. thetaiotaomicron; blue, mice colonized with E. coli hemA and then B. thetaiotaomicron. Individual CFU values are shown for each time point; the intersecting line represents the median of CFU for each cohort. The detection threshold was 5 × 10² CFU/g feces. ND, not detected. Data for mice where no CFU were detected are expanded at the baseline to distinguish the number of mice tested. (B) Anaerobic C. scindens (Cs) was administered as described above for panel A for the administration of E. coli to germfree animals, while a second group of mice received no C. scindens as a control. Sixteen hours later, both groups of mice received 10³ CFU B. thetaiotaomicron by oral administration. CFU determinations were performed at 8 h and 24 h p.i. (Left) C. scindens CFU at 8 h and 24 h in fecal samples of mice precolonized with this bacterium. (Right) B. thetaiotaomicron CFU at 8 h and 24 h in feces samples of mice with (+ Cs) or without (− Cs) C. scindens precolonization. Results of two independent experiments were pooled. Bars indicate median CFU per gram for the mice in each group. The detection threshold was 5 × 10² CFU/g feces. ND, below the detection level. *, P = 0.5; **, P = 0.05; ns, not significant.