Pathogenetic factors of Pseudomonas aeruginosa.

The virulence of Pseudomonas aeruginosa, which is easily differentiated from the two other most common pseudomonad pathogens, is low. This species primarily causes disease in patients with local anatomic changes or in the immune compromized hosts. A number of bacterial factors are involved in the pathogenesis of the microbe. Surface structures like the glycocalyx-capsular material-is involved in attachment to mucosal surfaces and resistance against phagocytosis and immunolysis of cells. The interference with bacterial components on mucociliar clearance of the bronchial tract have been described. In cystic fibrosis local environmental substances enhancing the production of capsular material have been described and the tendency for colonization of mucoid strains in cystic fibrosis probably is related to these factors. Another general component of gram-negative bacteria is endotoxin, but the toxicity of this cell wall constituent is relatively low in P. aeruginosa. A number of proteolytic enzymes with a probable role in disease have been described: collagenase, fibrinolysin, elastase, caseinase, and gelatinase. A proteolytic enzyme with activity against substances like casein, egg albumin, gluten, and haemoglobin has been described. A component like exotoxin A can produce skin lesions and antibodies produced with toxoid of exotoxin A are protective against this bacterial agent. Enterotoxin has been described based on rabbit intestinal loop preparations, but has not been further characterized and diarrhoea is rarely caused by P. aeruginosa. Haemolytic effect has been caused by a heat labile phospholipase C and by a heat stabile moiety. A leucocidin has been described: this may in part be capsular material. In addition, an exoenzyme S has been suggested as a virulence factor.