S224 17th ECCMID / 25th ICC, Posters (IP/IPI ratio of 8 and/or ellipse/phantom zone) were retested at the Reference Centre. A broad spectrum b-lactam MIC screen by Etest was also done. Veriﬁcation of MBL presence was done by PCR (blaIMP and blaVIM) and by spectrophotometric analysis of imipenem hydrolysis by crude cell extracts. As part of an ongoing study a subset of the strains (n = 10) was evaluated for changes in the transcription of oprD and mexB by quantitative RT-PCR. Results: Of the 31 MBL Etest positive isolates 7 were positive upon retesting. Interestingly, the IP MIC was reproducible while the IPI MIC was consistently increased, often by more than 2-fold dilutions. MBL production was veriﬁed in two isolates by PCR and hydrolysis of imipenem, resulting in 29 and 5 false-positive isolates in the initial and retesting respectively. Analysis of the resistance proﬁle of the isolates showed that additional selection criteria for MBL testing such as resistance to meropenem and/or ceftazidime using EUCAST breakpoints would reduce the number of false positives further. qRT-PCR on the subset of the isolates (n = 10) revealed a signiﬁcant downregulation of oprD (n = 6) and/or upregulation of mexB (n = 4) in the tested isolates. Conclusions: (i) In this study MBL Etest results were difﬁcult to reproduce and overestimated the presence of MBL in a low prevalence country like Norway. (ii) Additional selection criteria such as meropenem and/or ceftazidime resistance will reduce false-positive results and should be considered before more labour intensive analysis are performed. (iii) Gene transcription analyses indicate that decreased permeability and efﬂux are more prevalent mechanisms than MBL production in carbapenem resistant Norwegian P. aeruginosa isolates. (iv) False positive test results are probably due to the permeabilising effect of EDTA. P868 Occurrence of OXA-58 and an OXA-58 variant in Acinetobacter baumannii isolates from blood cultures in a university hospital in Athens, Greece I. Galani, V. Sakka, L. Galani, M. Souli, Z. Chryssouli, H. Giamarellou (Athens, GR) Objectives: Imipenem (IMP)-resistant A. baumannii isolates, collected from blood cultures of hospitalised patients in the University General Hospital “Attikon”, between September 2004 – May 2005, were studied for their clonality and carbapenemase content. Methods: Susceptibility to antimicrobials was determined using a broth microdilution method and E-test. Bacterial clones were identiﬁed by PFGE with ApaI. Metallo-b-lactamases were detected by the IMP- EDTA disc synergy test and by PCR with primers speciﬁc for blaVIM. Multiplex PCR with primers amplifying blaOXA-23-like, blaOXA-24- like, blaOXA-51-like and blaOXA-58-like, was performed according to Woodford et al (Int J Antimicrob Agents 2006; 27:351–353). Sequencing of cloned PCR products was performed by MWG-THE Genomic Company. Sequence similarity searches were carried out with the BLAST programme found at the website of the NCBI. Results: Twenty-seven non-repetitive IMP-resistant isolates, 70.2% of all A. baumannii strains isolated from blood cultures, were tested. All isolates presented a multi-resistance pattern, with all being susceptible to colistin (MICs: 0.125–0.75) and 33% being susceptible also to ampicillin/sulbactam. A. baumannii isolates were distributed into seven genotypes by PFGE proﬁles, with 12, 4, 4, 3, 2, 1, and 1 strains in each group. The three genotype-groups of 12 and 4 isolates were further divided into 2 subgroups. None of the isolates was positive for metallo- b-lactamase production by IMP-EDTA synergy test or PCR. Multiplex PCR for OXA-type carbapenemases revealed the presence of blaOXA- 51-like, which is believed to be intrinsic to A. baumannii and blaOXA- 58-like in all isolates. Sequencing of blaOXA-58 PCR amplicon revealed the presence of the blaOXA-58 in most of the isolates but also the existence of a novel variant of OXA-58 in which an A to G substitution revealed a Thr to Ala amino acid change. Conclusions: Several clones of IMP-resistant A. baumannii producing both blaOXA-58 and naturally occurring blaOXA-51-like have emerged as important bloodstream pathogens in our hospital. This observation emphasizes the importance of both the restriction of carbapenem usage as well as of the strict implementation of hand hygiene techniques for the containment of this emerging threat. P869 Spread of clinical extended-spectrum b-lactamase (CTX-M)-producing Escherichia coli in Portugal J. Leit˜ ao, N. Mendon¸ ca, V. Manageiro, D. Louro, E. Ferreira, M. Cani¸ ca on behalf of the Antimicrobial Resistance Surveillance Program in Portugal (ARSIP) Objectives: CTX-M extended-spectrum b-lactamases, which had a rapid growing and geographic dissemination, are the main recent cause of resistance to third-generation cephalosporins. The aim of this study was to characterise the resistance mechanisms to b-lactam antibiotics of clinical Escherichia coli strains, using phenotypic, biochemical and molecular approaches. Methods: During a 2-year period, started on March 2004, 181 nonrepetitive E. coli strains were isolated as ESBL producers from different clinical specimens at 9 hospitals from 3 different Portuguese regions. In this work, were only investigated the ESBL (CTX-M)- producing strains. Antimicrobial susceptibility was performed by broth- microdilution method. PCR and sequencing were used to screen and identify blaTEM, blaSHV, blaOXA, ampC and blaCTX-M genes. Biochemical characterisation was performed by isoelectric focusing. The genetic environment of blaCTX-M was characterised by PCR, regarding for ISEcp1, IS26 and IS903 elements. Strains were subtyped by using PFGE. Results: Of the 181 strains 119 (66%) were CTX-M producers. Susceptibility towards b-lactams conﬁrmed all isolates as ESBL producers, also suggesting CTX-M enzymes expression, which was corroborated by pI values. More than 98% of strains producing CTX-M group-1 were resistant to cefotaxime and ceftazidime, while all CTX-M group-9 producers were resistance to cefotaxime and 11% resistant to ceftazidime. Overall, multidrug-resistant (92%) strains were predominant in outpatients (50%) than inpatients (37%). PCR-sequence analysis conﬁrmed the presence of blaCTX-M-15 (n = 110) and blaCTX-M-32 (n = 1) genes from CTX-M-1 group, blaCTX-M-14 (n = 9) genes from CTX-M-9 group, blaTEM-1 (n = 104) and blaOXA-30 (n = 101). No strain carried the blaSHV gene. ISEcp1 elements were found upstream of all blaCTX-M genes and IS903 was detected downstream of one blaCTX-M-14 gene. Genetic relatedness analysis revealed 5 clusters and indicated that 76% of all isolates (from cluster IV) corresponded to a single epidemic strain. Conclusions: Our work conﬁrms the geographic spread in Portugal of CTX-M-type b-lactamases, mainly CTX-M-15, and suggests that the horizontal transfer of blaCTX-M genes, mediated by plasmids and/or mobile elements, contribute to the dissemination of those enzymes to community and hospital environments. Given the potent extended- spectrum activity of these enzymes, their continuous spread would have a distressing development. P870 GES-1 and TEM-1-like b-lactamases of Pseudomonas aerug- inosa strains isolated from patients in two Warsaw hospitals A.E. Laudy, A. Cieloch, D. Dzierzanowska, S. Tyski, J. Patzer (Warsaw, PL) Objectives: Ambler class A extended-spectrum b-lactamases are produced not only by Enterobacteriaceae family rods but also by P. aeruginosa strains isolated from clinical materials of hospitalised patients world wide. Recently, the presence of PER-1 enzymes produced by P. aeruginosa isolated in Poland has been described. The aim of the study was to identify strains producing TEM-, SHV-, GES- and VEB-type ESBLs, among P. aeruginosa isolated in Warsaw hospitals. Methods: The analysed 35 P. aeruginosa strains were isolated from clinical materials of patients in two Warsaw hospitals. The presence of ESBL in the strains was detected by a double-discs synergy test with inhibitors: clavulanic acid, sulbactam, tazobactam and imipenem.