FIG. 1.

Dendrograms of ESBL-producing K. pneumoniae (A) and E. coli (B) strains based on PFGE results. Twenty-nine strains of K. pneumoniae and nine strains of E. coli were included in the analysis. For PFGE analysis, the chromosomal DNA was digested with XbaI and electrophoresed in 1% agarose. The strains were clustered by the unweighted pair group method with arithmetic averages (UPGMA). The scale indicates the percentage of genetic similarity. The molecular size marker is a bacteriophage lambda ladder (Bio-Rad Laboratories, Inc.). The strain designations indicate the species (Kp, K. pneumoniae; Ec, E. coli), patterns of production of β-lactamases (A to K, as grouped in Table 6), year of isolation, and strain number.