Table 1. Virulence of Schu S4 derivatives in BALB/c mice.
| Strain | Route | Survivala | LD50 a , b | MTD (days)a |
| Schu S4 | i.n. | 0/5 | <10 | 6.6 |
| i.d. | 0/5 | <10 | 7.6 | |
| Schu S4 ΔpurMCD | i.n. | 5/5 | >106 | >21 |
| i.d. | 5/5 | >106 | >21 | |
| Schu S4 ΔpurMCD∶pTZ752 | i.n. | 0/5 | <10 | 6.8 |
| i.d. | 0/5 | <10 | 11.6 |
a
Survival, LD50, and mean time-to-death (MTD) were determined 21 days after infection for the lowest Schu S4 and Schu S4 ΔpurMCD∶pTZ752 doses (10 CFU) given, and the highest Schu S4 ΔpurMCD dose (106 CFU).
b
LD50 values were calculated as described by Reed and Muench.