| Plasmids of 'Legionella' Species (2006) | |||||||||||
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| Plasmids are extrachromosomal genetic elements that normally are not essential for survival of the host, but often carry genes which allow the host to compete more successfully in adverse environments. These genes code for many factors, the most medically important of which are toxin, drug resistance, and virulence factors. The possible involvement of plasmids in legionellosis was suggested by reports of cytotoxin and B-lactamase production and the virulent to avirulent conversion of Legionella pneumophila through serial passage on artificial media. Seventeen strains of L. pneumophila and 12 strains representing four other species of Legionella were screened for the presence of plasmid DNA by a variety of lysing procedures. Cryptic plasmids were isolated from: L. pneumophila (Atlanta-1, -2 and OLDA), L. bozemanii (WIGA), L. dumoffii (TEX-KL and NY-23) and L. gormanii (LS-13). The molecular weights of the plasmids ranged from 30-60 x 106 and the plasmid content of each strain was unique with respect to molecular weight and number of plasmid species. Plasmid DNA was not detected in the following strains: L. pneumophila (Philadelphia-1 through -4, Flint-1, Knoxville-1, Washington-1, Vermont-1, Pontiac-1, Togas-1, Bloomington-2, Los Angeles-1, Dallas-4 and Chicago-2) and L. micdadei (TATLOCK, HEBA, MI-15 and Pittsburgh pneumonia agent). | |||||||||||
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