P1697 Abstract (poster session) Characterisation of carbapenem non-susceptible Pseudomonas aeruginosa isolates in Danish hospitals; a nationwide study F. Hansen*, U.S. Justesen, C. Østergaard, H.K. Johansen, M. Arpi, D.S. Hansen, P. Littauer, A. Holm, O. Heltberg, H. Schumacher, K. Fuursted, M.-A. Lykke, B. Tønning, A.M. Hammerum (Copenhagen S, Odense, Aalborg, Copenhagen, Herlev, Hillerød, Hvidovre, Vejle, Slagelse, Herning, Aarhus, Esbjerg, Viborg, DK)

Objectives: In many European countries an increase in carbapenem non-susceptible Pseudomonas aerugionosa has been observed. Until 2011, no systematic data from Denmark had been registered, so a consecutive collection of carbapenem resistant P. aeruginosa was enacted, to investigate the carbapenem resistance mechanisms in Danish P. aeruginosa isolates. Methods: From January 1st 2011 through June 30th 2011, 116 nonreplicate, non-cystic fibrosis related P. aeruginosa isolates with reduced carbapenem susceptibility were collected from 12 out of 13 Danish Departments of Clinical Microbiology. The presence of acquired beta- lactamases was assessed using a combination tablet method, and the isolates were antimicrobial susceptibility tested against relevant antipseudomonal agents. Beta-lactamase subgroup specific PCR assays, subsequent sequencing analysis as well as an efflux pump inhibitor assay were performed. Results: Eight isolates produced the metallo-betalactamase VIM-2 and one isolate produced both OXA-10 and a VEB-group enzyme. Furthermore, 67 isolates displayed a derepressed AmpC phenotype, deduced from cloxacillin or boronic acid synergy with either ceftazidime or meropenem. Phenotypic indications of increased efflux pump activity were seen in 44 isolates. Efflux and AmpC positive results occurred more frequently in isolates resistant to both meropenem and imipenem than in isolates resistant only to imipenem. This suggests loss of porin as the main resistance mechanism in the imipenem resistance group of isolates. Activity of doripenem was less affected than that of meropenem in isolates with increased efflux activity. Resistance to ceftazidime and cefepime was primarily seen in the AmpC derepressed isolates. The rate of aminoglycoside resistance was relatively low against gentamicin (8%), amikacin (9%) and tobramycin (11%), while 56% were resistant to ciprofloxacin. Conclusion: Although relatively low in number, the occurrence of 8 VIM-2 producing isolates from six different hospitals stresses the necessity of a continued effort to detect and confirm isolates with a potential for spread of acquired beta-lactamases. Based on the phenotypic findings in this study, reduced permeability of the outer cell membrane and/or increased efflux pump activity, often in combination with overexpression of chromosomal AmpC, appeared to be the most likely main explanation for reduced carbapenem susceptibility in Danish P. aeruginosa isolates.