FIG 5.

Percent invasion (A), intracellular growth (IGC) (B), and percent total in vitro virulence (C) of L. monocytogenes strains C5, ScottA, and PL25 as determined using Caco-2 cells, after growth in TSB-Y at 10°C for 8 days without exposure to SGF (dark bars) or after growth in TSB-Y at 10°C for 8 days and subsequent exposure to SGF (pH 2.0, 37°C) for 30 min (light bars). Caco-2 cells were infected for 1 h with bacteria and incubated for 45 min (invasion) or 4 h (intracellular growth) with gentamicin. Total in vitro virulence was calculated as the percentage of initial bacteria recovered at the end of the assay. Data represent means ± standard errors of the means (SEM) of results of three biological replicates performed in triplicate. Asterisks (*) indicate significant differences between the results determined for a strain prior to and after exposure to SGF. Small letters indicate significant differences between strains prior to exposure to SGF. Capital letters indicate significant differences between strains after exposure to SGF (P < 0.05).