Multifocal emergence of ESBL-producing Klebsiella pneumoniae clone with differential non-carbapenemase-mediated resistance to carbapenems in Italian hospitals

Abstract number: P1700

D'Andrea M.M., Giani T., Arena F., Borgianni L., Gesu G., Li Bergoli M., Manso E., Mussap M., Sambri V., Sarti M., Luzzaro F., Rossolini G.M.

Background:Klebsiella pneumoniae is a major nosocomial pathogen. Carbapenems are among the few active drugs against multidrug-resistant (MDR) strains of K. pneumoniae producing extended-spectrum b-lactamases (ESBLs). Carbapenem resistance is increasingly reported in this species, being a matter of great clinical concern. In this work we report on the recent multifocal emergence, in several Italian hospitals, of an ESBL-producing K. pneumoniae clone with differential non-carbapenemase-mediated resistance to carbapenems.

Methods: Antimicrobial susceptibility was determined by disk diffusion and Etest. Clonal relatedness was investigated by PFGE of XbaI-digested genomic DNA. Carbapenemase activity was assayed spectrophotometrically. b-lactamase genes were investigated by PCR and sequencing. Outer membrane proteins (OMPs) were investigated by SDS-PAGE and by analysis of the corresponding genes.

Results: during 2007–08, ESBL-positive K. pneumoniae isolates showing a differential carbapenem resistance phenotype (resistance to ertapenem, reduced susceptibility to meropenem and susceptibility to imipenem) started to be reported from several Italian hospitals. We have investigated 22 nonreplicate isolates showing this phenotype from 6 different hospitals located in various Italian regions. Isolates were from bloodstream, lower respiratory tract, urinary tract and intra-abdominal infections. Carbapenemase activity and known carbapenemase genes were not detectable. All isolates produced the CTX-M-15 ESBL and resident SHV enzyme. Decreased expression of the k36 OMP was detected in all isolates. PAbN (40 mg/L) did not affect carbapenem MICs. PFGE analysis revealed a dominant clone (20 isolates) present in the 6 hospitals, plus one additional unrelated clone from a single hospital.

Conclusions: Although production of plasmid-encoded carbapenemases is the most common mechanism of carbapenem resistance in K. pneumoniae, strains with non-carbapenemase-mediated resistance have occasionally been described. To our best knowledge, this is the first evidence for multifocal clonal spread of ESBL-producing K. pneumoniae with a similar resistance phenotype. Clinical impact, and implications for detection and reporting by the clinical microbiology laboratory are discussed.

Session Details

Date: 16/05/2009
Time: 00:00-00:00
Session name: 19th European Congress of Clinical Microbiology and Infectious Diseases
Location: Helsinki, Finland, 16 - 19 May 2009
Presentation type:
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