Survival curves for ICR mice infected with the wild-type Sz35246 and ∆Island3-Sz35246. Two groups of eight-week-old ICR mice were inoculated i.p. with 2.5×105 CFU bacteria, and mouse survival was monitored over a 5-day period. Data are expressed as the mean percentage of live animals in each group (n = 10). The virulences of these two strains were significantly different (P<0.05).