TABLE 1.

Protection against wild-type Y. enterocolitica infection

Immunizing strain	No. of bacteria in tissues of mice 5 days after challengea
	Small intestine	Peyer’s patches	Spleen	Liver
WA(pYVO8-A-2)	(4.4 ± 0.2) × 102*	(3.0 ± 1.4) × 102*	0	0
WA-314 sodA	(1.9 ± 0.6) × 102*	(6.3 ± 1.5) × 102*	0	0
WA irp1	(8.9 ± 1.2) × 103*	(8.3 ± 0.8) × 103*	0	0
Controlb	(3.4 ± 1.7) × 105	(1.8 ± 0.9) × 106	(4.1 ± 0.8) × 105	(5.9 ± 1.2) × 104

^aGroups of eight mice were orally immunized with 10⁸ organisms of the indicated Yersinia mutant strain. Ten weeks after immunization, mice were orally challenged with 5 × 10⁸ (10 times the LD₅₀) Yersinia wild-type strain (WA-314) organisms. Five days after the challenge, the bacterial loads in organs of the mice were determined. Values are means ± standard deviations of data for eight animals. Values that differ from the control values at P < 0.05 are marked with asterisks. 

^bNonimmunized mice.