is an important pathogen in patients with cystic fibrosis (CF) and much is now known of its epidemiology. In contrast, its virulence mechanisms are poorly understood. The lipopolysaccharide (LPS) of , a well-recognised virulence factor of other gram-negative bacteria, is known to be strongly endotoxic . The aim of this study was to observe if there were any links between the structure of LPS and virulence. This has been investigated by polyacrylamide gel electrophoresis and immunoblotting to define the chemotype and antigenic cross reactivity of LPS. Strains (16) belonging to different genomovars of the complex were selected to represent epidemic and non-epidemic clinical isolates and environmental strains. All strains belonging to genomovars I and II (the latter now renamed ) had smooth LPS. However, isolates belonging to genomovar III, the group to which most of the epidemic CF isolates belong - including the highly transmissible strain (ET 12) which has been found in both the UK and North America - were of either rough or smooth LPS chemotype. In this study, J2315 represents the ET 12 lineage, and has a rough chemotype. Rabbit antiserum raised to strain J2315 revealed that the LPS core of this strain was antigenically related to some but not all other genomovar III strains, but it also cross-reacted strongly with all (genomovar II) and most genomovar I strains. Intra-strain phenotypic variation was demonstrated between bacteria grown in broth or on solid agar with a concomitant variation in antigenic cross reactivity. There was no clear evidence to associate any particular LPS phenotype with epidemic or non-epidemic strains, but changes in phenotype may provide clues to the survival and adaptability of in hostile environments and possibly to its ability to produce an inflammatory response .


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