Evolution of CTX-M-type β-lactamases in isolates of Escherichia coli infecting hospital and community patients

Escherichia coli isolates collected at our Institution from 1999 to 2003 (n = 20,258) were studied to evaluate the production of CTX-M-type extended-spectrum beta-lactamases (ESBL). Isolates suspected of producing CTX-M enzymes were analyzed by the double-disk synergy test, hybridization with specific probes, PCR and direct DNA sequencing. Overall, 53 ESBL-positive isolates were found to carry CTX-M-type genes (bla(CTX-M-1), n = 51; bla(CTX-M-15), n = 2). The isolation of CTX-M-positive strains increased from 1 per year (1999) to 26 per year (2003). The first isolate carrying the bla(CTX-M-15) gene appeared in 2003 and was obtained from a patient previously treated with ceftazidime. CTX-M-positive isolates were characterized by multi-drug resistance and were obtained both from inpatients (n = 29) and outpatients (n = 24). Most patients were over 60-year-old (n = 45), had underlying chronic diseases (n = 32), and had been hospitalized more than once (n = 33). Strains were frequently isolated from the urinary tract, often after recurrent infections. Our study demonstrates that CTX-M-producing isolates are increasing among E. coli strains. Adequate laboratory detection may help in choosing appropriate treatment and in limiting the spread of this resistance trait. (C) 2004 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved.