Bacterial lipopolysaccharides: candidate vaccines to prevent Neisseria meningitidis and Haemophilus influenzae infections.

Abstract

An exciting area of microbiological research over the past decade has been the progress made in the molecular characterisation of the cell surface carbohydrates of pathogenic bacteria. Many of these are important virulence factors, for example capsular polysaccharides, so that an understanding of their structure and function is crucial to investigations on pathogenesis of infectious diseases. Following from this, many carbohydrate structures on the cell surface of bacteria are ideal targets for therapy and immunoprophylaxis. Thus, the diverse and sometimes highly complex polysaccharides located in the bacterial cell wall or envelope that surround the fragile cytoplasmic membrane of the bacterial cell have been investigated in depth applying state-of-the-art technologies such as those available through molecular genetics and fine structural analyses. The bacterial cell wall, which is rigid, protects the membrane and the cytoplasm within from the adverse effects of the environment and is thus responsible for the resistance of the bacterial cells to mechanical and osmotic injury. It is the structure that provides the bacterial cell with its characteristic shape, whether spherical or rod-like. The cell wall is just one of the features distinguishing bacteria from animal cells which are enclosed only by a plasma membrane. There are marked differences in the composition of the cell walls of gram positive and gram negative bacteria. Both may have exopolysaccharides, often referred to as capsules, which, owing to their external location on the surface, often confer antigenic specificity which is useful in their classification. Walls of both classes of bacteria also contain peptidoglycan. Distinguishing facts are that gram positive organisms contain teichoic acids whereas lipopolysaccharides are typical of gram negative bacteria.