Different serum requirements for opsonization of two serologically identical strains of Pseudomonas aeruginosa

Two strains of serotype 2 Pseudomonas aeruginosa and one species of E. coli were compared regarding their opsonic requirements using human sera and polymorphonuclear leukocytes. None of the three organisms tested activated exclusively one complement pathway. Both strains of Pseudomonas had an absolute requirement for antibody for opsonization, but differed in complement requirements. The studies described herein showed significant differences in the mechanism of opsonization of the two strains of Pseudomonas.