21st European Congress of Clinical Microbiology and Infectious Diseases

Molecular characterisation and epidemiology of a carbapenem-resistant Enterobacteriaceae outbreak in a tertiary care centre, Istanbul

Abstract number: R2356

Yilmaz M., Aydin S., Mete B., Nazik H., Ongen B., Ozaras R., Saltoglu N., Mert A., Ozturk R., Tabak F.

Introduction: Bacteria from clinical and non-clinical settings are becoming increasingly resistant to conventional antibiotics. The increase in resistance of Gram-negative bacteria is mainly due to mobile genes on plasmids encoding carbapenem-hydrolyzing b-lactamases that can readily spread through bacterial populations. Here we describe a long lasting nosocomial outbreak of carbapenem-resistant Enterobacteriaceae strains expressing OXA-48.

Objectives: Between 2002 and 2010, we identified 42 Enterobacteriaceae strains that are resistant to any of the carbapenems in a 1500 bed university hospital. The aim of the study was to identify the resistance mechanisms for carbapenems in these strains and to check for clonal dissemination.

Methods: All the strains (29 Klebsiella pneumoniae, 6 Escherichia coli, and 7 Enterobacter spp.) were nonrepetitive clinical isolates from the Infectious Diseases and Clinical Microbiology Laboratory of Istanbul University, Cerrahpasa Medical Faculty. The strains were identified with the API 32GN system. Carbapenemase- and extended-spectrum-b-lactamase (ESBL)-encoding genes were identified by PCR experiments using previously designed primers for blaTEM, blaSHV, blaCTX-M, blaOXA-48, and blaVEB followed by sequencing. Isolates belonging to the same species were compared by pulsed-field gel electrophoresis. Transferability of b-lactamase genes were studied by conjugation experiments using an azide-resistant E. coli J53 as the recipient.

Results: All the carbapenem resistant strains isolated produced OXA-48, a class D oxacillinase with significant carbapenem-hydrolyzing activity. Many of the strains coproduced various b-lactamases (SHV-12, CTX-M-15 and TEM-1). Conjugation experiments were successful with K. pneumoniae isolates and all the transconjugants had decreased susceptibility to carbapenems. Isolates of the same species belonged to different pulsotypes.

Conclusion: The present work indicated that dissemination of the blaOXA-48 gene is not driven by the dissemination of a single clone but by dissemination of the blaOXA-48-carrying plasmid among Enterobacteriaceae during the last decade in our hospital. Since OXA-48 confers by itself a low level of resistance to carbapenems, clinical laboratory detection of OXA-48-producing strains may be difficult and the problem may actually be much bigger than it seems.