Infections with Pseudomonas aeruginosa in the compromised host

A review is given of the role of the various host defences in man against Pseudomonas aeruginosa and the mechanisms by which these are compromised in certain patient categories especially susceptible to serious Pseudomonas infections. The defects of host defences are usually complex and multiple, affecting various sites in the local and the systemic defences. Certain defects are emphasized, e.g. abnormalities of first line defences (skin, mucous membranes), and both quantitative and qualitative defects in polymorphonuclear granulocytes. However, it is also suggested that compromised functions of other components of antimicrobial defences may play a role in Pseudomonas infections, e.g. functional abnormalities in the systems of B cells. T cells and mononuclear phagocytes. Recent data suggesting mechanisms by which P. aeruginosa can exert suppressive effects on host defences, are mentioned, and the possibility of immunopathogenesis in Pseudomonas infections is discussed, particularly processes involving the complement system. Some important clinical features of Pseudomonas infections are described. The clinical peculiarities of bacterial infections in the severely neutropenic patient are emphasized, and exemplified with a brief description of Pseudomonas pneumonia. Finally, Pseudomonas septicaemia is mentioned with a brief discussion of certain important prognostic factors. It is concluded that a better understanding of the complex defense mechanisms against P. aeruginosa and therapeutic regimens by which they can be manipulated, is imperative to achieve any significant advances in the prevention and treatment of these infections.