Table 1.

Intracellular survival.

Hours penicillin treatment	Intracellular survival, % ± SD		Relative Survival
	1-4a	S31A1
2 h*	4.02 ± 1.96	0.69 ± 0.20	6.3
9 h	0.24 ± 0.05	0.16 ± 0.02	1.5
21 h	0.03 ± 0.02	0.04 ± 0.01	0.8

The S. zooepidemicus strains were co-cultured with HeLa cells. At 2 h post-infection cells were washed and media containing penicillin was added. The number of surviving bacteria was determined by plating 2, 9, and 21 h after penicillin had been added. Results were expressed as percentage survival (% recovered CFU divided by CFU at 0 h when penicillin was added), as described in Material and Methods. Means ± SD of three independent experiments are shown.

^*Significant difference between strains (p < 0.05). Relative Survival when the strains were compared (equation in Material and Methods).