C4A and infection: We detected and quantified C4-HSL in WT colonized mice at both day 4 and 7 p.i. and in both the cecum and colon (Figure 4(c,d); with an average of 0.10 and 12.80 ng/g in the cecum, and 3.71 and 21.50 ng/g in the colon at day 4 and 7 p.i., respectively), confirming C4-HSL as the dominant AHL produced by C. rodentium during infection.