Table 3.

Phenotype of a Dam⁻ mutant in the tissue culture model

Strain	Invasion, %†	Intracellular proliferation‡	Survival in macrophages*
			J774.A1	Mouse peritoneal
SL1344 (wt)	100  ±  23.8	25.3  ±  5.05	6.85  ±  0.3	0.41  ±  0.13
SV1610 (Dam−)	28.4  ±  9.2	16.1  ±  3.4	7.7  ±  1.65	0.22  ±  0.12
SV1610/pTP166	105.4  ±  33.9	28.9  ±  0.3	10  ±  0.53	0.33  ±  0.05
(Dam−/Dam+)
SB220 (SipC−)	0.43  ±  0.05	ND	ND	ND
SB302 (InvJ−)	0.65  ±  0.23	ND	ND	ND

^*Ratio of viable intracellular bacteria at 20 h vs. 0.5 h after infection. In both types of macrophages, cells were infected for 10 min. 

All values are averages of triplicate samples from at least two independent trials. ND, not determined. 

^†Percentage of bacteria that invade HeLa epithelial cells during 15 min and survived a gentamicin protection assay. Plating was done at 2 h after infection. Values were normalized to invasion rate of wild-type bacteria (0.109  ±  0.02). 

^‡Ratio of viable intracellular bacteria at 24 h vs. 2 h after infection, obtained after incubating HeLa cells with bacteria for 15 min.