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Scand J Infect Dis. 2012 Mar;44(3):174-81. doi: 10.3109/00365548.2011.632642.

Extended-spectrum β-lactamase (ESBL) in Danish clinical isolates of Escherichia coli and Klebsiella pneumoniae: prevalence, β-lactamase distribution, phylogroups, and co-resistance.

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Department of Clinical Microbiology, Hillerød Hospital, Hillerød, Denmark.



Most Gram-negative community-acquired and nosocomial infections are caused by Escherichia coli and Klebsiella pneumoniae, among which increasing resistance due to extended-spectrum β-lactamase (ESBL) is a major problem. We present data from the first Danish nationwide prevalence study on ESBL-producing E. coli, K. pneumoniae, and Proteus mirabilis in blood and urine cultures from hospitals and the community.


During September and October 2007, 13 of 15 Danish departments of clinical microbiology collected data and strains. Confirmatory ESBL test-positive isolates were sent to a central laboratory for species and ESBL-phenotype confirmation, extended susceptibility testing, phylogenetic grouping of E. coli strains, and ESBL gene characterization.


During the study, blood samples from 18,259 patients and urine samples from 47,504 patients were subjected to culture. Among 14,674 cultured isolates, 352 were confirmed to be ESBL-producers. Thus, the crude ESBL prevalence was 2.4% (range 1.5% of E. coli in community urine to 6.6% of K. pneumoniae in hospital urine). An average of 7.2 ESBL-producers per 100,000 consumed bed-days was calculated. Of the 352 reported ESBL-producers, 205 E. coli, 73 K. pneumoniae, and 1 P. mirabilis, were available for testing. CTX-M enzymes dominated, both in hospitals and in the community, occurring in 92% of E. coli and 88% of K. pneumoniae, and with CTX-M-15 constituting 60% and 77%, respectively.


Compared to 2003 data the ESBL prevalence in Denmark has increased significantly. In the ESBL-producers, reduced susceptibility towards both gentamicin and ciprofloxacin was seen among 43% E. coli and 55% K. pneumoniae, leaving clinicians in these cases with only a carbapenem for the treatment of serious infections. Part of this study was presented at the 20(th) European Congress of Clinical Microbiology and Infectious Diseases, abstract P-1617.

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