1 Department of Medical Microbiology, University of Thessalia, Mezourlo, Larissa; 2 Department of Microbiology, Faculty of Nursing, School of Health Sciences, University of Athens, 123 Papadiamantopoulou Street, 11527 Athens, Greece
Keywords: ESBLs , hospital-acquired infections , CTX-M ß-lactamases , Etest , PFGE , PCR , Greece
Sir,
Extended-spectrum ß-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.13 Recently, CTX-M-type ß-lactamases were reported among E. coli isolates from Greece.4
During February 2003February 2004, 426 E. coli isolates were recovered consecutively from hospital-acquired infections of separate patients hospitalized at the University Hospital of Larissa, Thessalia, Greece. Twenty-three (5.4%) of the isolates were confirmed as ESBL producers by the Etest ESBL screening method (AB Biodisk, Solna, Sweden) using cefotaxime and ceftazidime plus clavulanate. MICs of ß-lactams against these isolates were determined using Etest, whereas susceptibility testing against other antimicrobials was performed by the disc diffusion method on MuellerHinton agar.5 Against all but four of these isolates, the cefotaxime MIC was at least eight-fold higher than that of ceftazidime. Third-generation cephalosporins and aztreonam exhibited a notably variable efficacy against the ESBL producers (Table 1).
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The CTX-M-positive isolates were recovered from seven children and 13 adults who were hospitalized in seven different units of the hospital. Four of them had been treated with third-generation cephalosporins prior to the isolation. Sixteen of the patients had a severe urinary tract infection whereas the remaining four exhibited purulent infections.
This report documents the predominance of blaCTX-M genes among ESBL-positive E. coli recovered from clinical infections in a tertiary Greek hospital. The isolates exhibited plasmid-mediated resistance that affected the antimicrobial activity of penicillins and cephalosporins but also to several alternative antibiotics used to treat E. coli infections. The observation that different CTX-M subtypes, encoded by plasmids of varying size, are being carried by distinct strains of E. coli implies that the genes, and not simply the organisms carrying the genes, are spreading within our hospital. Our findings support the hypothesis that CTX-M enzymes will become the dominant ESBLs among E. coli worldwide. Since ESBL detection procedures are not always sensitive, the predominance of CTX-M enzymes suggests that it is important for our laboratories to perform synergy tests with cefpodoxime, which is degraded by TEM, SHV and CTX-M ESBLs.2
Footnotes
* Corresponding author. Tel: +30-210-7461483; Fax: +30-210-7461489; Email: atsakris{at}med.uoa.gr
References
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