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Chapter 11 : Phase Variation of Lipopolysaccharide and Other Virulence Determinants in Legionella pneumophila
Legionella pneumophila is an intracellular parasite of free-living amoeba species. In natural or man-made freshwater systems, L. pneumophila is frequently found in tight association with biofilms. In the human host, L. pneumophila is an intracellular pathogen of alveolar macrophages and blood monocytes. The authors have described the phase-variable expression of a lipopolysaccharide (LPS) epitope in L. pneumophila serogroup 1 strains. Associated with LPS phase variation, they observed the loss of virulence and serum resistance in the mutant strain. The profile of the primarily long-chain 3-hydroxylated fatty acids was shifted to shorter chains by about two carbons on average in phase-variant 811 compared with wild-type RC1. In the virulent wild-type strain RC1, the 30-kb element is located in the chromosome, whereas excision from the chromosome and replication as a high-copy plasmid resulted in the mutant phenotype. The colony material of the mutant strains is very sticky and appears slimy when suspended in aqueous solutions, which may facilitate adherence to and survival in biofilms outside a host cell and may protect the cells from dehydration as well.