TABLE 2.

Virulence and phagosomal escape efficiency of L. monocytogenes strains

Strain	50% Lethal dosea	Phagosomal escape (%)b	Plaque size (%)c
Wild type	5 × 104	51 ± 15	100
ΔLLOd	>1 × 109	0	NDe
LLO L461T	7.5 × 106	43 ± 9	100 ± 2f
LLO S44A	7.5 × 107	63 ± 9	14 ± 5
LLO S44A L461T	>1 × 108	58 ± 8	ND

^aThe 50% lethal dose is the quantity of bacteria injected into the tail vein that leads to the death of 50% of C57BL/6 mice.

^bThe percentage of phagosomal escape (mean ± standard deviation) is the percentage of actin-coated bacteria in all of the total bacteria at 90 min postinfection. A minumm of 200 bacterium-associated macrophages were counted.

^cThe plaque size, expressed as a percentage of the wild-type plaque size, in L2 monolayers after 3 days of of bacterial growth with 5 μg of gentamicin per ml. The values are means ± standard deviations.

^dStrain DP-L2161 (ΔLLO) has been described previously by Jones and Portnoy (25).

^eND, plaques are not measurable.

^fThe plaque size of the LLO L461T strain is sensitive to the gentamicin concentration, as described by Glomski et al. (19).