The aim of this study was to determine the virulence characteristics and resistance pattern of the extended-spectrum b
lactamases (ESBLs)-producing Escherichia coli strains isolated from urine of outpatients in the Zagreb region during a
five-month period, and to compare them with the non ESBLs-producing E. coli strains isolated in the same period. Out
of 2,451 E. coli strains isolated from urine of nonhospitalized patients with significant bacteriuria, a total of 39 ESBLsproducing
strains (1.59%) were detected by a double-disk diffusion technique and by the broth-dilution minimal inhibitory
concentration reduction method. The 45 non ESBLs-producing strains were randomly chosen, and phenotype of the
two groups of strains was characterized and compared. Serogroup O4, hemolysin production, expression of P- and type 1
fimbriae as well as resistance to gentamicin and amikacin were significantly more prevalent characteristics among the
ESBLs-producing strains than among non ESBLs-producing strains (p<0.01), while higher prevalence of trimethoprim-
sulfamethoxazole resistance among ESBLs-producing strains was not statistically significant (p>0.05). Chromosomal
DNA analysis by pulsed-field gel electrophoresis exhibited a great genomic similarity among ESBLs-producing
strains and revealed that those highly virulent and resistant E. coli strains isolated from urine of outpatients in the
Zagreb region had a clonal propagation
