FIGURE 4.

Phenotypic analysis of type-1 fimbrial expression in S. Typhimurium SL1344, ΔyqiC, and ΔyqiC′. (A) Yeast agglutination tests for S. Typhimurium strains incubated at 37°C. Formation of small agglutination fragments in S. Typhimurium SL1344 ΔyqiC indicated that the bacteria can express type-1 fimbriae and agglutinate with the yeast cells. The addition of 3% D-mannose interfered with receptor binding on the surface of S. Typhimurium SL1344 and ΔyqiC, which could not agglutinate with yeast cells to form small fragments, thus confirming that the yqiC deletion activated the expression of type-1 fimbriae. (B) The biofilm formation assay. S. Typhimurium SL1344, ΔyqiC and ΔyqiC′ were cultured in 96-well microplates at 37°C for 18 h. Then, all wells were washed with PBS and stained using 0.1% crystal violet for subsequent measurement of the absorbance detected at OD₅₅₀. The relative levels of biofilm formation in S. Typhimurium ΔyqiC and ΔyqiC′ were compared with those in S. Typhimurium SL1344 using the Student’s t-test. ^∗∗∗p < 0.001.