Opsonization and phagocytosis of mucoid and non-mucoid Pseudomonas aeruginosa strains.

The interaction between Pseudomonas aeruginosa strains (6 non-mucoid and 4 mucoid strains), serum factors and phagocytic cells was investigated. Strains were incubated in different concentrations of normal serum, chelated serum (with only the alternative complement pathway intact), IgG, Cls, C2 and C3 deficient serum and immune serum. After incubation complement consumption, C3 fixation and phagocytosis by polymorphonuclear leukocytes (PMN) were measured. In contrast to normal serum, immune serum raised against a mucoid and a non-mucoid strain exhibited heat-stable opsonic activity. All ten Pseudomonas aeruginosa strains were able to activate complement in 20% normal serum, leading to deposition of the activated form of the third complement component on the bacterial cell wall and to subsequent recognition and phagocytosis. One mucoid and four non-mucoid strains activated the alternative complement pathway and were effectively opsonized in chelated or in Cls, C2 or IgG deficient serum. Although mucoid strains were less able to activate complement via the alternative route, no differences were observed in opsonic requirements and phagocytosis between mucoid and non-mucoid strains.