SPI1 and infection: The role of AcrAB-TolC in the virulence of Salmonella Typhimurium is well established and inactivation of acrB causes a decreased expression of genes in Salmonella Pathogenicity Island (SPI-1), which are known to be required for infection.12,20,21,35 Nishino et al. 12 showed that the inactivation of acrD did not confer significant attenuation in the BALB/C mouse model of infection and the inactivation of acrEF (encoding the RND pump protein and the PAP) increased the host survival rate, with 20% of mice surviving to 21 days rather than none when infected with the WT strain.