To determine whether SsrB represses expression of SPI-1 during mouse infections, we tested the hilA-lux-740+350 transcriptional fusion in the WT S. Typhimurium strain, its isogenic ΔssrB mutant, and in the ΔssrB mutant complemented with a constitutive active SsrB variant in which aspartic acid 56 was replaced with glutamic acid. This evidence concerns the gene SPI1 and infection.