FIG. 7.

Invasion of Listeria spp. into MS9 and MS9II cells. Log-phase cultures of L. monocytogenes at a multiplicity of infection of 10:1 were incubated with MS9 and MS9II cells, and gentamicin was added to kill extracellular bacteria. Intracellular listerial cells were released by lysis of mammalian cells and recovered by plating onto media. Invasion was further investigated using listerial strains deficient in known virulence factors InlA and/or InlB. Percent relative invasion was calculated using the number of recovered listerial cells × 100%/the number of cells in the inoculum. Invasion of L. monocytogenes cocktail was significantly (**, P < 0.01) increased in MS9II cells compared to MS9 cell results. Invasion of L. monocytogenes strains lacking InlB was significantly reduced compared to the wt EGD strain results (*, P < 0.05). Noninvasive L. innocua was used as a control and was not recovered from lysed mammalian cells (not shown). Data presented are means ± standard deviations (n = 3 in duplicate).