Aim: To describe the risk factors and molecular epidemiology of nosocomial bloodstream infections caused by extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae in a tertiary care hospital. Methods: Patients with enterobacteria-positive blood cultures were included. ESBL expression in the isolates was detected using the combination disk method. Antimicrobial susceptibility testing was performed using the disk diffusion method. blaSHV, blaTEM, and blaCTX-M genes were identified in the isolated strains by PCR and sequencing. Klebsiella pneumoniae isolates were genotyped by PFGE. Results: Of the 90 isolates recovered, half were found to express ESBLs. Twenty-eight (62%) of these isolates were K. pneumoniae, 8 (18%) were Escherichia coli, 6 (13%) were Enterobacter cloacae, and 3 (7%) were Serratia marcescens. Multivariate logistic regression analysis showed that the only independent risk factor associated with infection by ESBL-producing strains was use of broad-spectrum cephalosporins. None of the isolates was resistant to imipenem. The blaSHV5 gene was detected in 84% of isolates, followed by blaCTX-M15 (27%), blaSHV2 (9%), and blaSHV12 (7%). PFGE identified six clones among the 28 ESBL-producing K. pneumoniae isolates. Conclusions: ESBL-producing K. pneumoniae clones were detected throughout the hospital. Use of broad-spectrum cephalosporins is the most important risk factor associated with the proliferation of ESBL-producing strains.

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