FIG. 1.

The BarA-UvrY two-component system regulates the virulence of E. coli O78:K80:H9 in chicken embryos. The lethality of E. coli K-12 DH5α (control), χ7122 (wild type [wt]), SM3000 (barA::kan) (▪), SM3001 (uvrY::cm) (▴), SM3002 (barA::kan uvrY::cm) (×), SM3003 (barA::kan) carrying pSM1 (□), and SM3004 (uvrY::cm) carrying pSM2 (▵) was determined by inoculating 0.1 ml of 5 × 10 ³ CFU of bacteria into the allantoic cavity of a set of 20 12-day-old embryonated chicken eggs. Bacterial strains were grown in LB broth to an optical density at 600 nm of 1.5 at 37°C for 48 h without shaking. Cells were washed and gently resuspended in phosphate-buffered saline. Bacterial suspension in 0.1 ml of PBS was injected into the allantoic cavities of embryonated eggs using an 18-gauge needle, and the hole was subsequently sealed with glue. The eggs were incubated at 37°C and examined every 12 h for 7 days. The first time that each embryo was first observed to be dead (no movement on candling) was recorded. The results are the means of two such experiments.