Figure 5
The effects of AutA and AutR on acid resistance and K1 capsule antigen of DE205B phenotype.
(A) Acid resistance assays were performed to determine the survival rates among mutants and complemented strains compared to that of DE205B. Logarithmic growing E. coli cells were exposed to pH 2.0 for 2 h. Percent survival for bacterial acid resistance was measured by plate counting with three biological replicates. In parallel, tenfold serial dilutions of bacterial cells exposed to acid challenge were spotted onto LB agar plates. The pH 7.4 treated cells were used as a control. Statistical significance analysis was performed using one-way ANOVA (*P < 0.01). (B) Detection of K1 capsule expression of DE205B and several variants. The K1 capsule-specific antiserum was used to conduct the ELISA to detect the capsule antigen. The ELISA result of DE205BΔkps1 mutant strain acted as the negative control. Statistical significance analysis was performed by the Student t test (*P < 0.01). (C) To support the accuracy of the ELISA results, the microscopic observation to detect the K1 capsule among DE205B and variants. After stained, the K1 capsule of bacteria was colorless and the encapsulated or nonencapsulated E. coli was indicated. DE205BΔkps1 mutant strain acted as the negative control.
