Glucosylation of the O antigen contributes to acid resistance.

<p>(A) LPS profiles of S. <i>flexneri</i> 2457T (wt) and MSF2743 (Δ<i>gtrABII</i>). 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. (B) Acid resistance of S. <i>flexneri</i> 2457T (wt), MSF2743 (Δ<i>gtrABII</i>) and MSF2743/pMM111 (Δ<i>gtrABII</i>/<i>gtrABII</i>⁺). 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> <0.05).