Virulence associated ingestion of Legionella pneumophila by HeLa cells.

Invasion of HeLa cell monolayers by Legionella pneumophila was studied. Virulent L. pneumophila strains efficiently entered cultured HeLa cells whereas isogenic avirulent isolates were nearly 1000-fold less efficient at cellular entry. Animal passage of avirulent strains, which restored bacterial virulence, coincided with a return to the virulent parental level of HeLa cell invasion. Diminished HeLa cell invasion by avirulent strains was not a function of reduced bacterial association with the cell monolayer. These data suggest that ingestion of L. pneumophila by non-professional phagocytes is a virulence directed property.