β-lactamases are the commonest cause of a resistance of gram-negative bacteria to β-lactam antimicrobial agents. The introduction of the third- and fourth- generation cephalosporins into clinical practise is the reason of an evolution of new β-lactamases being able to hydrolyze these antibiotics. Extended-spectrum β-lactamases (ESBLs) are the major group of these enzymes. Most of the ESBLs are mainly structural mutants of penicillinases TEM-1, TEM-2 and SHV-1. For several reasons, ESBL-producing isolates should, by definition, be reported as resistant to all penicillins, cephalosporins and monolactams. Due to seriously reduced antibiotic choice for infections caused by ESBL-producing bacteria, ESBLs pose a serious clinical problem. This review will focus on the characterization and identification of ESBLs, interpretation of sensitivity testing results of ESBL producing bacteria and an appropriate treatment of infections caused by ESBL-producers

        Key words: resistance – cephalosporins – β-lactamases – enterobacteria – ESBL.