Figure. Pulsed-field gel electrophoresis of XbaI-digested genomic DNA of O157 VTEC PT2 isolated from outbreaks in 1995. Digests were separated on 1% agarose for 42h at a voltage gradient of 5.6 volts per cm with a pulse ramp time of 5 to 50 sec. Lane 1 contained a phage lambda DNA 48.5 kb ladder (Sigma). Lanes 2 to 8 contained digests of PT2 strains from outbreaks as follows: lane2, outbreak 1; lane3, outbreak 2; lane4, outbreak 4; lane5, outbreak 5; lane6, outbreak 6; lane7, outbreak 8; lane8, outbreak 9.