RESUMEN
Crude aqueous extract was obtained from acetone-dried cells of Pseudomonas aeruginosa strain 868 (serogroup O2, Lányi and Bergan's schema) and subjected to ultracentrifugation (105,000 g, 3 h); the lipopolysaccharide (LPS)-containing precipitate was discarded and the supernatant containing water-soluble cell proteins was subjected to further fractionation. From a partially purified aqueous extract two fractions were obtained by step-wise precipitation with ammonium sulphate, namely, F1 (by 50% saturation), and F2 (by 80% saturation). By gel and ion-exchange chromatography from both fractions 9 subfractions were isolated differing in molecular weight, protein content, and LPS contamination. Subfractions 4 and 7 were practically free from LPS, and gave one precipitation line with antisera for strain 868. By immunoelectrophoresis subfraction 4 contained 2 cathodic and 1 anodic, whereas subfraction 7 mainly 1 anodic component. These subfractions were antigenically identical. With ELISA these subfractions were less active as compared to other subfractions, in particular to those of high molecular weight. The anti-subfraction 4 and anti-subfraction 7 sera were found to protect passively mice against intraperitoneal challenge by P. aeruginosa strain 8 (serogroup O2). These data support the authors' opinion that subfraction SF-4 and SF-7 are protective protein antigens (mol wt about 40,000 and 30,000, respectively), that are localized in the outer membrane of P. aeruginosa cell envelope.