Adherence of knockout mutants compared to the wild type strain. The wild type and mutant strains were incubated for 2 hours with D562 cells and the number of adherent bacteria was determined. The adherence of mutants is given as mean adherence counts from 12 replicate wells (x-axis). Error bars are 95% confidence intervals observed among the replicates. All means differ significantly from the wild type at p < 0.001.