resistant , and baumannii clinical isolates in a tertiary hospital V. Papaioannou, S. Tsiplakou, A. Stylianakis, E. Chatziandreou, I. Papadakis, D. Argyris, P. Thomaidis, K. Mouta. Microbiology Laboratory, KAT Hospital, Athens, Greece

Objectives Carbapenemase-producing Gram-negative have increased substantially. The aim of this study was to evaluate carbapenem-resistant Klebsiella pneumoniae, Pseudomonas aeruginosa and Acinetobacter baumannii isolates derived from clinical samples in a tertiary hospital.

Methods A total of 310 strains of K. pneumoniae, 224 of P. aeruginosa and 324 of A. baumannii were studied. Isolates were recovered from blood cultures, body fluids, catheters, pus, bronchial secretions and urine samples derived from hospitalized patients (ICUs and surgical and medical wards), during one year, from 01/11/10 to 31/10/11. 118 out of 310 K. pneumoniae isolates were recovered from ICU patients’ samples while the number for P. aeruginosa isolates was 96 out of 224 and for A. baumannii 209 out of 324 respectively. All isolates had and/or MICs > 1mg/ml. The identification and susceptibility testing was performed via the Vitek II automated system (Biomerieux, France), and when necessary susceptibility results were confirmed with the use of E-test strips (AB Biodisc, Sweden) according to CLSI guidelines. Metallo-β-lactamase (MBL) production was evaluated using disks containing meropenem with and without EDTA and KPC-production with boronic acid combined-cisk tests, using disks containing meropenem with and without boronic acid.

Results All isolates were multidrug resistant. K. pneumoniae isolates revealed 11% resistance to gentamicin, 8% to and 40% to . With reference to carbapenemase production, 61 isolates were producing MBL and the rest 249 were producing KPC. 75 out of 310 K. pneumoniae isolates were recovered from blood samples. As for P. aeruginosa (38 out of 224 being recovered from blood samples), resistance to gentamicin was at 75%, and to colistin at 4%. 181 out of 224 isolates were producing MBL. A. baumannii isolates (72 out of 324 being recovered from blood samples), revealed resistance to gentamicin at 58%, to tigecycline at 39% and to colistin at 2%.

Conclusion It is of great importance to monitor the emergence and prevalence of carbapenem resistant Gram-negative bacteria depending not only on susceptibility testing but on phenotypic detection of carbapenemase production as well, in order to choose appropriate empiric therapy according to existing information and adjust individual antimicrobial chemotherapy when necessary.