Serological and genotypic diversity among serogroup 5- reacting environmental Legionella isolates

Abstract

Five strains of bacteria (strains 684, 687, U7W, U8W, and MICU-B) that were biochemically and morphologically indistinguishable from Legionella pneumophila were recovered from the environment. Strains U7W, U8W, and MICU-B were antigenically identical to L. pneumophila strain Dallas 1E (serogroup 5), as determined by direct fluorescent antibody staining and immunodiffusion. Although strains 694 and 687 shared antigenic determinants with L. pneumophila Dallas 1E, they could be distinguished by immunodiffusion and differential absorption studies. However, as determined by DNA hybridization, the antigenically distinct strains 684 and 687 belong to the same DNA homology cluster as previously described authentic strains of L. pneumophila, whereas strains U7W, U8W, and MICU-B belong to a separate homology group. Therefore, two groups could be identified among these environmental isolates; one represents an antigenic subclass of serogroup 5 L. pneumophila (strains 684 and 687), and the other, although antigenically indistinguishable from serogroup 5 L. pneumophila, probably represents a new Legionella species (strains U7W, U8W, and MICU-B).

Genetic structure of populations of Legionella pneumophila

“…Inasmuch as Dallas 1E has been widely used in research as a reference strain for serogroup 5 (11), a discrepancy regarding its identity must be accounted for. Garrity et al (16) reported relative binding rates for Dallas 1E with Philadelphia 1 of 94 and 93% at 64 and 75C, respectively, and the reciprocal experiment yielded values of 94 and 95% at 64 and 75°C, respectively. With L. pneumophila isolate 684 (ATCC 33733; ET-44) as reference, Dallas 1E showed relative binding rates of 77 and 69% at 64 and 75°C, respectively.…”

“…(ii) Species 2. Species 2 is known only from three environmental isolates, MICU-B, U7W, and U8W (ATCC 33735 through 33737), collected at the Pittsburgh Veterans Administration Medical Center and extensively studied by Garrity et al (16). Each isolate has a distinctive electromorph profile (Table 2), but all three ETs are very closely related (Fig.…”

“…Notwithstanding the considerable genetic difference between isolates of species 2 and L. pneumophila, Garrity et al (16) reported that serotyping and tests of 10 phenotypic characters failed to distinguish these isolates. These authors concluded that U7W, U8W, and MICU-B "are probably members of another species" but advised against making a formal taxonomic change until "additional serological or biochemical methods become available to differentiate these strains from L. pneumophila" (16). Our analysis confirms the genetic distinctness of these three isolates from L. pneumophila.…”

“…In the virtual absence of information on the genetic relationships of isolates, research on L. pneumophila has heretofore been conducted within a framework provided by serotyping. Although heterogeneity of antigenic types has been detected by differential absorption and immunodiffusion of sera (7,16,62), only nine serogroups have been distinguished by conventional serological methods, and most isolates are serogroup 1 (35). Consequently, serotyping has been of limited use in distinguishing clones in epidemiological, systematic, and population genetics research.…”

Plasmid and surface antigen markers of endemic and epidemic Legionella pneumophila strains

“…The primary plasmids of Legionellaceae. Lanes: 1, L. pneumophilc isolation and identification techniques used have been Atlanta 4; 2, L. pneumophila PUH 6; 3, L. pneumo described previously (5,6).…”