SipA, SopA, SopB, SopD and SopE2 effector proteins of Salmonella enterica serovar Typhimurium are synthesized at late stages of infection in mice

Salmonella pathogenicity island (SPI)-1 is essential for invasion of non-phagocytic cells, whereas
SPI-2 is required for intracellular survival and proliferation in phagocytes. Some SPI-1 effectors,
however, are induced upon invasion of both phagocytic and non-phagocytic cells, suggesting
that they may also be required post-invasion. In the present work, the presence was analysed of
SipA, SopA, SopB, SopD and SopE2 effector proteins of Salmonella enterica serovar Typhimurium
in vitro and in vivo during murine salmonellosis. Tagged (36FLAG) strains of S. enterica
serovar Typhimurium were inoculated intraperitoneally or intragastrically to BALB/c mice and
recovered from the spleen and mesenteric lymph nodes of moribund mice. Tagged proteins were
detected by SDS-PAGE and immunoblotting with anti-FLAG antibodies. In vitro experiments
showed that SPI-1 effector proteins SipA, SopA, SopB, SopD and SopE2 were secreted under
SPI-1 conditions. Interestingly, it was found that S. enterica serovar Typhimurium continued to
synthesize SipA, SopB, SopD and SopE2 in colonized organs for several days, regardless of the
route of inoculation. Together, these results indicate that SPI-1 effector proteins may participate in
the late stages of Salmonella infection in mice.