A clinical isolate of Escherichia coli LBT04 was found to have a high-level resistance to broad-spectrum β-lactams. Analysis of this strain by the disk diffusion test revealed synergies between clavulanic acid and ceftazidime, cefotaxime. Clavulanic acid decreased the MICs of ceftazidime, cefotaxime, and ceftriaxone, which suggested that LBT04 produced an extended-spectrum β-lactamase. These resistances were carried by a 1080-bp chromosomal gene that encoded a β-lactamase with a pI of 6.3. Cloning and sequencing experiments showed that this β-lactamase revealed identity with the bla_TEM-1 gene encoding the TEM-1 β-lactamase, except for a replacement of the Glu residue at position 104 by Lys, and of the Gly residue at position 238 by Ser. These two mutations were encountered in TEM-15 β-lactamase, but this is the first description of this enzyme in the E. coli species in Tunisian hospitals. To cite this article: C. Chouchani et al., C. R. Biologies 330 (2007).