S1 nuclease PFGE-based sizing of large plasmids for 8 clinical isolates. A) Agarose gel showing S1 nuclease PFGE-based sizing of large plasmids for 8 isolates. M indicates the Lambda molecular weight marker. Plasmid size preparations from isolate number 08, 20, 25, 135, 141, 214 and 175 reveal plasmids with sizes ranging from 25 kb to 485 kb which are indicated with arrowheads; B) shows the corresponding gel after southern blotting and DIG hybridization. Hybridized plasmids are indicated with arrowheads. A small plasmid is labeled with SP; its size of 25 kb was determined after digestion with HindIII, BamHI and EcoRI (data not shown).