PFGE of total DNA from K. pneumoniae and ESBL-producing E. aerogenes cut by XbaI. Lanes: A, lambda ladder; B, K. pneumoniae with no ESBL (strain 1′); C and D, ESBL-producing K. pneumoniae (strains 10 and 13, respectively); E and F, E. aerogenes (strains 2 and 14, respectively). The size of the ladder is indicated in kilobases.