Characterization of extended-spectrum β-lactamases-producingKlebsiella pneumoniae isolates of two intensive care units Background: Extended-spectrum β-lactamase (ESBL)-producing Klebsiella pneumonia is more the frequently implied bacterium infections nosocomiales in the Neonatal High Risk Unit (NHRU), and adult intensive care unit (aICU) in the The Andes University Hospital Autonomy Institute.Aim: To determine the microbiological and molecular characteristics associated with infections caused by this bacterium.Material and Methods: 17 strains of K. pneumoniae isolated from neonates from NHRU with nosocomial infections and 11 isolates from patients hospitalized in the aICU between June to November 2009 were characterized by in vitro agar diffusion test and MIC, the production of β-lactamase, the presence of bla TEM , bla SHV y bla CTX-M genes and genotyping.Results: A high percentage of resistance to β-lactams and the presence of ESβL TEM, SHV and CTX-M in 41.2 y 82% of strains obtained at HRNU and at aICU respectively were detected.BLEE (+) phenotype was detected in 17,6% of HRNU strains and 91% of aICU strains.Genotypic analysis by REP-PCR detected several clones suggesting that resistant clones of ESBL-producing K. pneumoniae are endemic not only specific circulation and transmission of a single common among patients.Conclusion: K. pneumoniae strains that produce b-lactamases circulate in these critical units studied representing a therapeutic challenge that is necessary to fight against.