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Emergence of carbapenem-non-susceptible extended-spectrum-beta-lactamase (ESBL)-producing Klebsiella pneumoniae isolates at the university hospital of Tübingen, Germany

¹ Institute of Medical Microbiology and Hygiene, University of Tuebingen, Germany;

² Max Planck Institute for Developmental Biology, Department I, Protein Evolution, Tuebingen, Germany;

³ Proteome Centre Tuebingen, Interfaculty Institute of Cell Biology, University of Tuebingen;

⁴ Robert-Koch-Institute, Wernigerode, Germany

⁵ E-mail: sabine.groebner{at}med.uni-tuebingen.de

Received August 13, 2008
Accepted March 10, 2009

The spread of gram-negative bacteria with plasmid-mediated extended-spectrum beta-lactamases (ESBL) has become a worldwide problem. In the present study we have analysed a total of 366 ESBL-producing Enterobacteriaceae strains isolated from any patients' specimen at the university hospital of Tübingen in the period from January 2003 to December 2007. Although the overall ESBL rate was comparatively low (1.6%), the percentages of ESBL-producing Enterobacter spp. and Escherichia coli increased from 0.8% and 0.5%, respectively, in 2003 to 4.6% and 3.8%, respectively, in 2007. In particular, we have observed the emergence of one carbapenem-resistant ESBL-producing E. coli isolate and five carbapenem-non-susceptible ESBL-positive Klebsiella pneumoniae isolates, in two of which carbapenem resistance development was documented in vivo under a meropenem-containing antibiotic regime. The possible underlaying mechanism for the carbapenem-resistance in three of the K. pneumoniae isolates was loss of the Klebsiella porin channel OmpK36 as shown by PCR analysis. The remaining two K. pneumoniae isolates exhibited an increased expression of a tripartite AcrAB-TolC efflux pump as demonstrated by SDS-page and mass spectrometry analysis of bacterial outer membrane extracts, which, in addition to other unknown mechanisms, might contribute to further increase the carbapenem MIC values. Carbapenem-non-susceptible ESBL isolates might pose a new problem in the future due to possible outbreak situations and limited antibiotic treatment options. Therefore, a systematic exploration for intestinal colonisation with ESBL should be reconsidered, at least for haemato-oncological departments where four of the overall five carbapenem-non-susceptible ESBL isolates originated from.