Studies on the uptake and intracellular replication of Legionella pneumophila in protozoa and in macrophage-like cells

Abstract

Legionella pneumophila strains isolated from different sources were tested for their host range in the protists Acanthamoeba castellanii, Hartmannella vermiformis and Entamoeba histolytica. It has been shown that A. castellanii and H. vermiformis but not E. histolytica support the intracellular replication of L. pneumophila. Furthermore it could be demonstrated that in vivo virulence in the guinea pig and the intracellular growth in U937 cells coincides with the capability to replicate intracellularly in A. castellanii at 37°C. The infectivity of L. pneumophila that had sustained a 48 hours nutrient deprivation was not significantly different from that of legionellae grown to log-phase on BCYE plates. In contrast the nutrient limitation on A. castellanii increased the amount of intracellular legionellae at the beginning of infection. An initial opsonin independent attachement stage of legionellae to U937 cells was demonstrated by scanning electron microscopy. In contrast, L. pneumophila's capability of stable or long term attachmennt to A. castellanii was shown to be inefficient.