LISTERIA-MONOCYTOGENES P60 SUPPORTS HOST-CELL INVASION BY AND IN-VIVOSURVIVAL OF ATTENUATED SALMONELLA-TYPHIMURIUM

The extracellular protein p60 is a major virulence factor of the intra cellular bacterium Listeria monocytogenes. Its roles in pathogen survi val in vivo and host cell invasion in vitro were studied. To this end, Salmonella typhimurium SL7207 was used as carrier for secreted p60-Hl yA fusion protein by Escherichia coli HlyB and HlyD transport proteins . C57BL/6 mice infected intravenously with this strain suffered from i ncreased bacterial numbers in livers and spleens compared with the p60 -nonexpressing control strain, but only transiently. In vitro experime nts showed that p60 promotes invasion of recombinant S. typhimurium SL 7207 p60 into hepatocytes and resting macrophages independent from com plement. Moreover, the uptake of wild-type L. monocytogenes EGD and L. monocytogenes BUG 8, an internalin-deficient strain, into hepatocytes was partially blocked by anti-p60 antibodies. The impaired invasion o f dissociated bacterial chains of L. monocytogenes RIII, a p60 express ion mutant, into hepatocytes and macrophages was partially restored by addition of p60 or p60-HlyA-enriched bacterial supernatants. These da ta suggest that the L. monocytogenes surface-associated proteins, p60 and internalin, act in concert to achieve optimal uptake into nonprofe ssional phagocytes and macrophages. Together, these experiments reveal a substantial impact of p60 on cell invasion and virulence and thus e mphasize the importance of the intracellular habitat for survival of L . monocytogenes in the host.