The genetic structure of populations of LegioneUa pneumophila was defined by an analysis of electrophoreticaily demonstrable allelic variation at structural genes encoding 22 enzymes in 292 isolates from clinical and environmental sources. Nineteen of the loci were polymorphic, and 62 distinctive electrophoretic types (ETs), representing multilocus genotypes, were identified. Principal coordinates and clustering analyses demonstrated that isolates received as L. pneumophila were a heterogeneous array of genotypes that included two previously undescribed species. For 50 ETs of L. pneumophila (strict sense), mean genetic diversity per locus was 0.312, and diversity was equivalent in ETs represented by isolates recovered from clinical sources and those collected from environmental sources. Cluster analysis revealed four major groups or lineages of ETs in L. pneumophila. Genetic diversity among ETs of the same serotype was, on average, 93% of that in the total sample of ETs.

A panel of monoclonal antibodies to Legionella pneumophila serogroup 1 and a subclassification scheme were developed in a collaborative project among three laboratories. The seven most useful monoclonal antibodies were selected from three previously developed panels on the basis. of indirect fluorescent antibody patterns with 83 strains of L. pneumophila serogroup 1 that were obtained from widely distributed geographic locations. The isolates were divided into 10 major subgroups on the basis of reactivity patterns that can be readily reproduced in any laboratory and are not subject to major inconsistencies of interpretation of staining intensity. A standard protocol for the indirect fluorescent antibody procedure was also developed.

In the period August 10-29, 1986, 29 confirmed cases of Legionnaires' disease occurred in Sheboygan, Wisconsin; two cases were fatal. No common source of indoor exposure was identified. Water specimens were obtained from all known cooling tower units in Sheboygan; Legionella pneumophila serogroup 1 was isolated at 1 x 10(6) colony-forming units per liter from a specimen obtained August 27 at plant A. This isolate was identical to the only clinical isolate by monoclonal antibody and isoenzyme subgrouping. Of 29 persons with Legionnaires' disease, 21 lived or worked within one mile (1.6 km) of plant A; seven of the remaining eight visited within one to two miles (1.6 to 3.2 km) of plant A from three to seven days before onset of illness. Attack rates were highest for persons living within 0.5 mile (0.8 km) of plant A. These findings associate a cooling tower with community-acquired Legionnaires' disease and suggest that dissemination of Legionella may occur over longer than previously recognized distances.

Two "rickettsia-like organisms," TATLOCK and HEBA, isolated from human blood via guinea pigs and embryonated eggs in 1943 and 1959, respectively, have been cultured on artificial media (charcoal yeast extract agar) for the first time and characterized. TATLOCK and HEBA have identical cultural, biochemical, and antigenic characteristics, as well as identical cellular fatty-acid composition and antimicrobial susceptibilities. These two bacteria have most of the cultural and biochemical characteristics of Legionella pneumophilia, and their gas-liquid chromatography cellular fatty-acid profile is similar to that of WIGA, another bacterium similar to L. pneumophila. Direct fluorescent-antibody reagents prepared for HEBA and TATLOCK gave equal high-titered reciprocal staining and were negative on 220 other bacteria, including L. pneumophila. Deoxyribonucleic acid relatedness studies, however, showed that these bacteria are not genetically related to either L. pneumophila or the WIGA bacterium.

A new species of bacteria that is an etiologic agent of human pneumonia has been isolated and characterized. Clinical symptoms of infection with this organism are not readily distinguishable from those caused by Legionella pneumophila infection. The organism was isolated from respiratory tract specimens from four patients. Two cases of infection apparently originated in California and one in Georgia, and a fourth was of unknown geographic origin. The name Legionella longbeachae species nova is proposed for this organism. The type strain of L. longbeachae is Long Beach 4 (= American Type Culture Collection 33462).