PFGE patterns of S. dysenteriae type 1 strains isolated from Kolkata after digesting genomic DNA with the XbaI restriction endonuclease enzyme. Lanes M, 48.5-kb concatemers of bacteriophage λ DNA (Bio-Rad, Hercules, Calif.) used as molecular size standards; lane 1, outbreak strain (X1 pulsotype); lanes 2 to 4, 6 to 8, and 10 to 12, strains from hospitalized cases (X1 pulsotype); lane 5, hospital strain (X1₁ subtype); lane 9, hospital strain (X1₂ subtype); lane 13, smearing of DNA.