SPI1 and infection: In addition, high fluid shear levels may also upregulate expression of SPI-1 protein regulators (such as those encoded by the hil and rts genes) and the SPI-1 T3SS apparatus (inv genes), thereby facilitating the delivery of SPI-5 and SPI-1 effector proteins (including those encoded by the sip, sop, and sic genes), thus potentiating the infection.