Table 2.

Protection conferred by a S. typhimurium Dam⁻ mutant to challenge with the virulent strain

Experiment	Dose of SV1610 (Dam−)*	Challenge dose of SL1344 (wt)†	No. dead mice/ inoculated mice
1	—	2.8  ×  103	1/5
	—	2.8  ×  104	1/5
	—	2.8  ×  105	4/5
2	2.5  ×  106	1.2  ×  106	1/4
	2.5  ×  107	1.2  ×  106	1/4
	2.5  ×  108	1.2  ×  106	0/4
3	7  ×  106	9.7  ×  106	0/5
	7  ×  107	9.7  ×  106	1/5
	7  ×  108	9.7  ×  106	0/5
	89  (i.p.)	9.7  ×  106	0/5
	890  (i.p.)	9.7  ×  106	0/5
	8.900  (i.p.)	9.7  ×  106	1/5

^*Inoculations were done by the oral route, except when indicated i.p. After 4 wk, all Dam⁻ infected mice survived the doses of bacteria indicated. 

^†All inoculations were done by the oral route. In experiments 2 and 3, challenges with the wild-type strain were done 4 wk after the inoculation with the Dam⁻ mutant. Mouse survival was recorded for 4 additional weeks.