FIG. 3.

Invasion of epithelial cells. Bacteria were grown overnight as standing cultures in LB broth buffered with 100 mM MOPS, pH 6.7, and with either 10 mM sodium chloride (gray bars) or 10 mM sodium formate (black bars). Bacteria were added to HEp-2 cells, and the level of invasion was assessed by using a gentamicin protection assay. Invasion is shown in comparison to that of the wild-type strain set to 100. Each strain and condition was tested in quadruplicate. Single asterisks show a significant difference (P ≤ 0.05) for the strain with the genotype shown when grown with the addition of formate compared to the NaCl control. Double asterisks show a significant difference for the mutant strain compared to the wild type when both were grown without formate. Error bars show standard deviations.