Isolation of a Serogroup I-Specific Antigen from Legionella pneumophila

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Abstract
Outer membrane material was extracted from a serogroup 1 strain of L. pneumophila using ethylenediaminetetraacetate. Ferritin-conjugated antiserum reacted only at the surface of the organism, as seen by EM. Outer membrane material was fractionated into 5 peaks by molecular sieve chromatography using a gel that had been equilibrated in a buffer containing sodium deoxycholate. One resolved peak (.apprx. 4 .times. 104 daltons) was highly active serologically. When rechromatographed in the absence of sodium deoxycholate, material from this peak reaggregated to .apprx. 106 daltons. The serologic activity of this antigen was restricted to L. pneumophila serogroup 1, although minor cross-reactions with strains of serogroups 2 and 4 were detected using an enzyme-linked immunosorbent assay. The antigen was < 10% carbohydrate, 15% protein. 1.1% phosphate and the remainder lipid of unknown composition. Neither 2-keto-3-deoxyoctonate nor heptose was detected; the antigen did not induce a Shwartzman reaction. Only 1 band was seen on sodium dodecyl sulfate-polyacrylamide gel electrophoresis.