FIG. 2.

Biofilm formation by serovar Typhimurium strain BJ2710 or serovar Typhimurium BJ3402 (BJ2710 ΔwcaM) on cultured HEp-2 cells. The composite image of biofilm formed by adherent serovar Typhimurium strain BJ2710 (A) or nonadherent BJ2508 (BJ2710 fimH) (C) was captured after 24 h of incubation. Panel B is a biofilm formed by the BJ3402 (BJ2710 ΔwcaM) mutant strain, and panel D is a biofilm formed by BJ3402 (BJ2710 ΔwcaM) complemented with plasmid pNAL100 (wcaM⁺). Panel A demonstrates that extensive biofilm is formed by strain BJ2710. Mutation of the wcaM gene (B) results in a thin, short biofilm across the surface of the HEp-2 cells. As a negative control, disruption of the fimH gene yields virtually no bacterial accumulation at all (C). Bacteria were labeled with GFP (green) and the HEp-2 cells with CMTMR (red), and colocalization of bacteria with cells appears yellow. Slanted images provide a perspective of the depth of the biofilm.