The <i>S. flexneri</i> S-OAg is required for acid resistance.

<p>LPS profiles (A) and acid resistance (B) of <i>S. flexneri</i> 2457T, mutants in the chain length regulators and mutants complemented with homologous or heterologous chain length regulators. Strains are 2457T (wt), MSF102 (Δ<i>wzzB</i>), MSF107 (Δ<i>wzz</i>_pHS2::<i>aph</i>), MSF209 (Δ<i>wzzB</i> Δ<i>wzz</i>_pHS2::<i>aph</i>), MSF209/pJC139, MSF209/pJC144, MSF209/pMM110 and MSF209/pJC142. LPS samples from equal numbers of bacterial cells (1×10⁷ CFU) were loaded in each lane and were analyzed by Tricine-SDS-polyacrylamide gel electrophoresis on a 14% (w/v) acrylamide gel followed by silver staining. For acid resistance assays, cells were grown overnight in citrate-buffered LB (pH 5.5) and diluted 1∶1000 into the acid-challenge media. Survival is stated as a percentage of the inoculum. Averages±standard errors (error bars) are shown. Statistical significance was determined by a Student's <i>t</i> test. (**, <i>P</i> <0.01, ***, <i>P</i> <0.001).