Replacement of an agr group I clone by an agr group II clone, as shown by PFGE of consecutive isolates (from the sputum of a CF patient, collected from November 1994 to November 1999) after SmaI digestion of chromosomal DNA. The agr group I clone was isolated for 17 months before the agr group II clone was isolated for the first time in April 1996. Then, the agr group I clone was isolated only once again (December 1996), with some differences in fragment patterns, after it was replaced by the agr group II clone.