The Role of Structure and Invasiveness on the Pathogenicity of Legionella

The pathogenic mechanisms and virulence factors involved in infections with Legionella are little understood. In vitro studies by thin-section and scanning electron microscopy show that legionella organisms attach to mammalian cells in culture, are taken into cytoplasmic vacuoles lined with ribosomes and replicate, probably utilising cell-derived amino acids. The presence of pili (fimbriae), lipopolysaccharide and protein structures at the bacterial surfaces is no doubt related to the initial adhesion to cell surface receptors. Motility through flagella and toxin production add to the potential invasiveness of these bacteria. Intracellular longterm survival and replication in alveolar macrophages affords a mechanism for increasing bacterial infectivity while avoiding the host's immune system, amplifying microbial pathogenicitiy.