Cloning and expression of a common Legionella outer membrane antigen in Escherichia coli

A genomic library of Legionella pneumophila was constructed by inserting L. pneumophila knoxville-1 strain (LPK-1) chromosome fragments into cosmid vector pHC79. Screening of the library with antibodies directed against a major outer membrane protein/lipopolysaccharide complex from LPK-1 resulted in the identification of six clones that reacted with the antiserum. Western blot analysis indicated that a 19,000 dalton (19 kDa) component was the reactive antigen in all of the clones. Western blot analysis of outer membranes from L. pneumophila serogroups and other Legionella species revealed that the cloned 19 kDa antigen was common to all serogroups and all but one of the five other Legionella species examined. One of the 19 kDa expressing clones was used as an immunoabsorbent to recover antibody to the 19 kDa antigen thus confirming the surface localization of this L. pneumophila antigen in E. coli.