Legionnaires' disease bacterium isolated in 1947.

The results of serologic, cultural, and DNA relatedness studies have shown that the Legionnaires' disease (LD) bacterium and an unclassified agent isolated in 1947 are the same species. Both organisms grew on charcoal-yeast extract agar, enriched Mueller-Hinton agar, and F-G agar, but neither grew on blood agar, trypticase soy agar, or in thioglycollate broth. Both agents reacted with convalescent sera from patients with Legionnaires' disease and convalescent sera from guinea pigs infected experimentally with the LD bacterium. The percentage of guanine plus cytosine in DNA preparations from each organism was ascertained by thermal denaturation to be 39%. In DNA hybridization reactions the 1947 isolate showed the same degree of relatedness to Philadelphia 1 strain of the LD bacterium as did three recent isolates of the bacterium. The LD bacterium was also shown to be antigenically related to another unclassified organism isolated in 1959.