THE CLPC ATPASE OF LISTERIA-MONOCYTOGENES IS A GENERAL STRESS PROTEINREQUIRED FOR VIRULENCE AND PROMOTING EARLY BACTERIAL ESCAPE FROM THE PHAGOSOME OF MACROPHAGES

Under stress conditions, the facultative intracellular pathogen Lister ia monocytogenes produces a ClpC ATPase, which is a general stress pro tein encoded by clpC and belonging to the HSP-100/Clp family, A ClpC-d eficient mutant was obtained by gene disruption in strain LO28, which became highly susceptible to stress conditions in vitro, Intracellular growth of this mutant was restricted within macrophages, one of the m ajor target cells of L. monocytogenes, during the infectious process, A quantitative electron microscope study showed that, contrary to wild -type bacteria that rapidly gain access to the cytoplasm of macrophage s, mutant bacteria remained confined to membrane-bound phagosomes. Onl y a few mutant bacteria disrupted the phagosome membrane after 4 h of incubation, then polymerized actin filaments and multiplied within the cytoplasm, The ClpC ATPase, therefore, promotes early bacterial escap e from the phagosome of macrophages, thus enhancing intracellular surv ival, The ClpC ATPase was produced in vivo during experimental infecti on by wild-type bacteria, The virulence of the ClpC-deficient mutant w as severely attenuated in mice, with a three-log decrease in its 50% l ethal dose compared with wild-type bacteria. Bacterial growth of mutan t bacteria was strongly restricted in organs, presumably because of an impairment of intracellular survival in host tissues, Our results pro vide evidence that a general stress protein is required for the virule nce of L. monocytogenes, which behaves as a virulence factor promoting intracellular survival of this pathogen.