Legionella pneumophila sp. nov.: The Legionnaires' Disease Bacterium 



LDB strains Togas 1, Bloomington 1, and Bloomington 2 were at least 80% related to 

 Philadelpliia 1 in reactions done at 60°C. These results are significant in tiiat botli the Togus and 

 Bloomington isolates were serologically atypical and/or isolated from the environment. Togus 1 is 

 the first strain whose O antigen does not react with the direct fluorescent antibody conjugate to 

 LDB Knoxville (12). Bloomington 1 reacts with the Knoxville conjugate, but was isolated from 

 the environment {14). Although Bloomington 2 is also an environmental isolate, it is serologically 

 different from both Knoxville and Togus 1 {12. 14). 



It is an impossible task to prove directly that LDB is different from all described species at 

 the level of species, genus, and family. Our approach to this problem was to assume that LDB 

 could not be related to organisms that had GC content in their DNA outside the range of 35% to 

 45%, or were gram-positive, strict anaerobes, spore fomiers, psychrophiles, thennophiles, acido- 

 philes, or alkalinophiles. One can argue with any of these criteria, but the alternative is an 

 irrational screening approach. 



Genera containing one or more species still under consideration for some level of relatedness 

 to LDB are listed in Table 4. Direct or indirect DNA relatedness results can be used to rule out at 

 least most species in these genera except for those of Aciiietobacter. Bdelloribrio. B rani nun el la. 

 Fle.xithri.x. Kingella. Microscilla. Moraxella, and Simousiella. There are persuasive reasons to 

 exclude these remaining genera. For example, Biwihemella are cocci; Fle.xithri.x are catalase 

 negative, gelatin negative, and grow well at alkaline pH. One cannot, however, rule out the 

 possibility that LDB is related to these genera at the family level. Therefore, species in all of these 

 genera should be tested for DNA relatedness to LDB. 



Table 4. 



Genera in which relatedness to Legionella pneumophila sp. nov. 



has not been totallv ruled out 



Acinetobacter 



ActinobacHlus 



Bdellcribrio 



BrauliamcUa 



Cytophaga 



Flavobacterium 



Francisella 



Flexihacter 



Fle.xithri.x 



Haemophilus 



Kingella 

 Microscilla 

 Mora.xella 

 Pasteurella 

 Simon siella 



It is unlikely that the LDB is related to any well-described pathogen. We believe that the 

 LDB is a previously undescribed species. Its biochemical reactions, growth pattern, and DNA 

 relatedness are sufficiently unique to warrant placing it in a new genus. The fact that to date LDB 

 is apparently totally unrelated to other organisms is consistent with the creation of a new family. 



We have proposed the name Legionella pneumophila McDade et al. (//) sp. nov. for the 

 LDB. Le-gi-on-ella. M.L. Icgio M.L.n. legion or army;M.L. dim. ending ella. pneu-moph"ila. Gr. 

 n. pneinno lung; Gr. adj. philos loving (4). The type strain of Legionella pneumophila is Phila- 

 delphia 1. Legionella pneumophila was proposed as the type species of the genus Legionella. 

 Legionella was proposed as the type genus for a new family Legioneilaceae (4). 



SUMMARY 



DNA from strains of the LDB was characterized in order to aid in the proper classification 

 of this organism. The genome size of LDB DNA was estimated at 2.5 X 10'' daltons by reasso- 

 ciation kinetics; a GC content of 39% for LDB DNA was established by optical thennal denatura- 

 tion and buoyant density ultracentrifugation measurements. 



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