Non-toxic determinants of virulence

Non-toxic determinants of virulence:

Some substances from bacteria aided the establishment of invasive infection. These were termed as aggressins. Investigations recognized numerous substances and their capability to act as determinants of virulence. Antisera provide protection against infection with the equivalent organism.


The capsular polysaccharides of pneumococci and M proteins of Streptococcus pyogenes; both subdued phagocytosis; while the pneumococcal capsule created a thick mechanical barrier and denied access of complement to the surface of the organism. The M protein created only a thin surface layer though prevented opsonization. It is now considered to hinder the access of complement by binding fibrinogen to the streptococcal surface. Other pathogens have been established to possess surface components related with virulence, most of them polysaccharides. Such included the K antigens of enterobacteria and the capsular polysaccharides of Haemophilus influenzae and Neisseria meningitidis. Different actions were attributed to them. In addition to the inhibition of phagocytosis, such show antigenic mimicry of host tissue.

The role in pathogenesis of loose extracellular slime not aggregated about individual bacteria has been acknowledged more recently. Dextrans formed by oral streptococci contribute to the creation of dental plaque. Slime-forming coagulase-negative staphylococci are now supposed to initiate the formation of ‘vegetations’ on prosthetic devices. The alginate slime of mucoid strains of Pseudomonas aeruginosa appears to help colonization of the respiratory tract in cystic fibrosis patients.


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