The effect of Pseudomonas aeruginosa on the immunogenicity of enterobacterial common antigen.

Pseudomonas aeruginosa produces a factor (PF) which alters the enterobacterial common antigen (ECA). Its effect on the immunogenicity of two types of immunogenic ECA, namely, the ethanol-soluble preparation freed of lipopolysaccharide and the LPS-coupled form from the R-mutant E. coli 014 was investigated. The antibody response following intravenous immunization was determined by means of the hemagglutination test. It is shown that PF abolishes the immunogenicity of the former but not of the latter. PF obtained from a strain of P. maltophilia yielded the same results. Antiserum against Pseudomonas aeruginosa of types 1 and 6 neutralizes PF produced by either type. These results suggest that PF alters the lipid part and not the haptenic determinant of ECA and that this activity is neutralized by P. aeruginosa antiserum of either type 1 or type 6. This interpretation is compatible with the identification of PF as a lipase.