CTX-M enzymes are the most common extended-spectrum -lactamases among Escherichia coli in a tertiary Greek hospital

1Department of Medical Microbiology, University of Thessalia, Mezourlo, Larissa; 2Department of Microbiology, Faculty of Nursing, School of Health Sciences, University of Athens, 123 Papadiamantopoulou Street, 11527 Athens, Greece Sir, Extended-spectrum β-lactamases (ESBLs) have emerged among Gram-negative bacteria; predominantly Klebsiella pneumoniae and, to a lesser extent, Escherichia coli and other species. Most ESBLs are mutants of the classical TEM and SHV enzymes, but since 1995 a rapid increase in the number of CTX-M variants has been reported among enterobacterial isolates from hospitalized patients.1 CTX-M enzymes hydrolyse and confer resistance to cefotaxime preferentially over ceftazidime and exhibit a higher susceptibility to tazobactam than to clavulanic acid. Currently, the CTX-M family includes almost 40 variants, divided between five major amino acid sequence subtypes (see www.lahey.org/studies/other.asp#table1).1 They are most prevalent in South America and the Far East, but have also been disseminated in several European countries.1–3 Recently, CTX-M-type β-lactamases were reported among E. coli isolates from Greece.4