ABSENCE OF AN EARLY DETECTABLE INCREASE IN HEAT-SHOCK PROTEIN-SYNTHESIS BY LISTERIA-MONOCYTOGENES WITHIN MOUSE MONONUCLEAR PHAGOCYTES

We investigated the behaviour of Listeria monocytogenes during the ear ly phase of its in vitro phagocytosis by mouse resident peritoneal mac rophages, and compared behaviour and modifications in protein synthesi s occurring in a virulent and a non-virulent strain of L. monocytogene s. As previously shown, these two strains have differential responses to stress and heat shock in vitro. At between 1 and 3 h of phagocytosi s, there is a general decrease in protein synthesis in Listeria. Synth esis of the major DnaK and GroEL heat-shock proteins also decreases. S ynthesis of only a limited set of bacterial proteins is conserved or e ven increased during this early phase of phagocytosis. Similar modific ations in protein synthesis are also observed in bacteria which have h ad only transient contact with macrophages without being phagocytosed. The discrimination, by the macrophage, between non-virulent and virul ent L. monocytogenes occurs less than 30 min after initiation of phago cytosis: avirulent Listeria are totally degraded inside the resident p eritoneal macrophages, whereas a significant fraction of virulent List eria remain undamaged and alive. The distinct behaviour of the two str ains of Listeria thus appears to be independent of a drastic change in bacterial protein biosynthesis.