Emergence of Klebsiella pneumoniae with an AmpC and blaSHV-11 in a Belgian hospital

Abstract number: 1733_169

Vanwynsberghe T., Boel A., Cartuyvels R., Raymaekers M., De Beenhouwer H.

Objectives: From August to October 2006 we observed 12 unrelated clinical isolates of Klebsiella pneumoniae expressing an unusual antibiotic susceptibility pattern. Characterisation of these strains was performed.

Methods: Isolates were found in routine because of flagging by Phoenix® (BD) as ``possible extended-spectrum bèta-lactamases (ESBL) positive''. Identification was confirmed by 16S rDNA sequencing. Control testing for ESBL was done with a modified double-disk synergy method also including cefoxitin. In order to verify the presence of an AmpC b-lactamase, the AmpC disk test presented by Black et al (2005), was performed. The clinical isolates were examined for the presence of blaTEM, blaTEM-24, blaSHV and blaCTX-M by polymerase chain reaction (PCR), using consensus primers for the different genes. Furthermore typing with pulsed field gel electrophoresis was performed.

Results: Strains were confirmed as Klebsiella pneumoniae. All were cefoxitin-resistant. A resistance-induction phenomenon potentiated by amoxicillin-clavulanic acid was observed with cefotaxime and aztreonam. Besides that, scattered colonies were found in the inhibition zones of ceftazidime, ceftriaxone, aztreonam, cefotaxime, and amoxicillin-clavulanic acid, but not for cefepime. On the other hand the cefepime inhibition zone showed a phantom zone in the neighbourhood of amoxicillin-clavulanic acid.

The cefoxitin-resistance leads to only a few possible causes of the expressed pattern: porin loss, AmpC b-lactamase production, or carbapenemase production (metallo-b-lactamase) are all described. In these strains the AmpC disk test was positive pointing to the presence of an AmpC b-lactamase. Furthermore the molecular investigation showed the presence of the blaSHV-11 gene, a gene which is not classified as an ESBL-producing gene.

Strains of Klebsiella pneumoniae containing SHV-11 and an AmpC b-lactamase are rare and have been described mainly in Taiwan. Until now strains producing these enzymes have been found rarely on other continents. However in the Far East the prevalence of AmpC b-lactamases in Klebsiella pneumoniae is rising.

Characteristics of the first strain discovered

MIC in mg/mL; inhibition zone (Ø) in mm. AMC: amoxicillin-clavulanic acid; ATM: aztreonam; CAZ: ceftazidim; CRO: ceftriaxone; CTX: cefotaxime; FEP: cefepime; FOX: cefoxitin.aScattered colonies in the inhibition zone; bflattening of the inhibition zone towards AMC; cphantom zone present towards AMC.

Conclusion: Based on the phenotype and the molecular findings an AmpC b-lactamase together with SHV-11 is very suggestive. Strains of Klebsiella pneumoniae harbouring the combination of the blaSHV-11 gene and an AmpC gene are infrequently found in Europe.

Session Details

Date: 31/03/2007
Time: 00:00-00:00
Session name: European Society of Clinical Microbiology and Infectious Diseases
Location: ICC, Munich, Germany
Presentation type:
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