FIG. 1.

Caco-2 cell invasion efficiencies of 24 L. monocytogenes isolates, from the subset of 203 isolates characterized by the Caco-2 cell invasion assay described herein, that demonstrated reproducibly attenuated invasion (see Table S1 in the supplemental material). The invasion efficiencies of L. monocytogenes isolates were normalized to that of a standard laboratory control strain, 10403S (the level of invasion by this strain was set at 100%), which was included in each invasion assay. Columns represent the average invasion efficiency observed for each isolate, and error bars indicate the minimum and maximum invasion efficiencies observed for each isolate. The presence of PMSC types 4 through 7 is noted above the names of the isolates carrying each respective mutation. A one-sample t test was applied to compare the invasion efficiency of each isolate to that of 10403S. Different letters indicate the presence or absence of statistical significance, defined by P of <0.05. Specifically, isolates denoted by a did not show significantly reduced invasion (P > 0.05), whereas isolates denoted by b showed significantly reduced efficiencies of invasion (P < 0.05) of Caco-2 cells compared to that of 10403S. All L. monocytogenes isolates harboring PMSC mutations in inlA had significantly reduced invasion (P < 0.02) of Caco-2 cells. FSL J2-076 displayed attenuated invasion of Caco-2 cells that was associated with the presence of a PMSC in sigB (31) rather than a PMSC in inlA.