Fluorescein labelled phalloidin

The F-actin cytoskeleton was labelled with fluoresceinlabelled phalloidin (Coconier et al., 2000) . Briefly, monolayers of Caco-2/TC-7 cells prepared on glass coverslips were incubated for 1 h with 0.5 ml selected Lactobacillus strains (1×10 8 cfu/well). Next, monolayers were washed twice with PBS and were subsequently infected with Salmonella (1×10 8 cfu/well) for 1 h. After infection, cells were washed with PBS and fixed with 3% (w/v) paraformaldehyde in PBS for 15 min. Samples were then treated with 50 mM NH 4 Cl for 10 min to block aldehyde functions, permeabilised for 4 min with Triton X-100, and incubated for 45 min with 1 μg/ml fluorescein-labelled phalloidin (Sigma-Aldrich). Then, the coverslips were mounted in 50% (v/v) glycerol-0.1% (v/v) sodium azide in PBS. Samples were examined by an inverted microscope system (Nikon TI-Eclipse) coupled to NIS-Elements imaging software (Nikon Instruments Inc., Tokyo, Japan).