CHARACTERIZATION AND CLONING OF A 37.6-KB PLASMID CARRIED BY LEGIONELLA-PNEUMOPHILA RECOVERED FROM PATIENTS AND HOSPITAL WATER OVER A 12-YEAR PERIOD

For 12 years, strains of Legionella pneumophila serogroup 1 harbouring a 37.6-kb (23 MDa) plasmid have predominated among patient and potabl e water isolates at the Victoria General Hospital, Halifax, N.S. Plasm id DNA recovered from 24 strains isolated between 1983 and 1995 was di gested with the restriction endonucleases EcoRI, HindIII, KpnI, PvuII, XbaI, and BamHI. The distribution of cutting sites indicated that the 23-MDa size group had remained essentially unchanged during this peri od, suggesting the persistence of a single plasmid type. Further fragm entation pattern analysis permitted the construction of a physical map of the prototype 23-MDA plasmid, pLp4269. Double digestion with BamHI -HindIII enabled the cloning of 94.4% of pLp4269 into pBluescript vect or. A 2.1-kb fragment was not clonable. Plasmid pLp4269 is the first o f the smaller Legionella extrachromosomal DNAs to be characterized in this way.