Subtyping of Legionella pneumophila serogroup 1 isolates by small-fragment restriction endonuclease analysis.

Whole cell DNA of Legionella pneumophila isolates was examined by small-fragment restriction endonuclease analysis (SF-REA). Fourteen serogroup 1 isolates from tap water in one hospital collected before and after eradication measures had been taken were compared with control strains of serogroup 1 and other serogroups that were not epidemiologically linked. DNA was digested with EcoRI and electrophoresed on polyacrylamide gels. The gel patterns were made visible by silver staining and analysed by direct visual comparison. All 15 epidemiologically unrelated strains of Legionella pneumophila serogroup 1 and of other serogroups exhibited different restriction fragment patterns. The isolates from the hospital could be clearly subdivided into two groups by SF-REA, suggesting that the hot water supply of the hospital was contaminated with two different strains. SF-REA performed on Legionella pneumophila serogroup 1 DNA enabled further subtyping of these organisms and thus appears to be a useful technique for investigating their epidemiology.