SERPINB6 and infection: However since the SPI1&2o mutant showed reduced ability to colonise the spleen 4 days post infection when compared with the wild-type S. Enteritidis infection, this shows that SPI-3, SPI-4 and SPI-5 collectively influenced the virulence of S. Enteritidis for chickens although these 3 SPIs individually did not contribute to the ability of S. Enteritidis to colonise the spleen of infected chickens.