Thirty-five strains of Legionnaires' disease bacteria were shown to belong in four distinct serologic groups on the basis of findings obtained with direct fluorescent antibody testing. Thirty of the strains were placed in group 1, three in group 2, one in group 3, and one in group 4. Immunoelectrophoretic studies showed both unique and common antigens among the representative strains of the four serogroups.

A bacterium with growth characteristics similar to, but genetically distinct from, either Legionella pneumophila or WIGA (a "rickettsia-like agent") was obtained from a postmortem lung specimen of a patient with fatal atypical pneumonia at the M. D. Anderson Hospital and Tumor Institute in Houston, Texas. This bacterium and WIGA have essentially the same cellular fatty acid composition, which is distinct from that of L. pneumophila. Deoxyribonucleic acid-reletadness studies show that the isolate from Texas is only about 10% related to both L. pneumophila and WIGA and there fore may represent a new species. This new bacterium should be considered in selecting laboratory procedures in the diagnosis of atypical pneumonia.

No abstract

A strain of the Legionnaires disease bacterium (LDB) that was isolated by Joseph E. McDade from a postmortem lung specimen of a patient with fatal atypical pneumonia at the Veterans Administration Hospital in Togus, Maine was serologically different from 16 other strains of LDB that had been isolated previously from patients in other geographic locations. The serological differences of the Togus isolate were shown in results of direct and indirect fluorescent antibody staining and of immunoelectrophoresis with soluble antigen extracts. Seroconversion for the Togus strain of LDB in acute- and convalescent-phase sera from a second patient with atypical pneumonia at the Veterans Administration Hospital in Togus indicated that this patient had been infected with an LDB that was serologically similar or identical to the Togus isolate. The Togus serogroup of LDB should be considered when performing serological tests for Legionnaires disease.