Journal of Chemotherapy Vol. 18 - n. 1 (20-26) - 2006 © E.S.I.F.T. srl - Firenze ISSN 1120-009X INTRODUCTION During the past decade, enterococci have emerged as important causes of nosocomial and community-acquired infections, with Enterococcus faecalis and Enterococcus faecium being the most important implicated species 1-3 . Enterococci have intrinsic resistance to many antimicrobial agents, including aminoglycosides, clindamycin, the anti- staphylococcal penicillins (oxacillin and methicillin), cephalosporins and most fluoroquinolones. In addi- tion, the ability of enterococci to develop or acquire resistance to other agents, mainly through the trans- fer of plasmids and transposons, chromosomal exchange, or mutation is well recognized 2,4-6 . Through such mechanisms enterococci have acquired additional resistance to high concentrations of aminoglycosides, as well as to β -lactams, macrolides, tetracycline, chloramphenicol, and more recently to glycopeptides such as vancomycin and teicoplanin 2,7-9 . A large number of different resistance determi- nants have been identified in enterococci, and, in several cases, they are located on conjugative plas- mids or transposons 2,4,6,10 . In this sense, a wide variety of genes encoding aminoglycoside-modifying enzymes have been detected in high-level aminogly- coside resistant enterococci, such us aac(6´)-aph(2”), Antibiotic Resistance and Mechanisms Implicated in Clinical Enterococci in a Tunisian Hospital N. KLIBI 1,2 - S. GHARBI 1 - A. MASMOUDI 3 - K. BEN SLAMA 1 - P. POETA 2 - M. ZARAZAGA 2 - C. FENDRI 3 - A. BOUDABOUS 1 - C. TORRES 2 1 Laboratoire de Microbiologie, Département de Biologie, Faculté de Sciences de Tunis, Campus Universitaire, 2092 Tunis, Tunisia; 2 Area de Bioquímica y Biología Molecular, Universidad de La Rioja, 26006 Logroño, Spain; 3 Laboratoire de Bacteriologie, Hôpital la Rabta, Tunis, Tunisia. Corresponding author: Carmen Torres, Area de Bioquímica y Biología Molecular, Universidad de La Rioja, Madre de Dios, 51, 26006 Logroño, Spain. FAX: +34-941299721; Phone: +34-941299750. E-mail: carmen.torres@daa.unirioja.es Summary Susceptibility testing for 15 antibiotics was performed in a series of 191 clinical enterococci recovered in a Tunisian Hospital during 2000-2003. Species detected were the following ones (number of isolates): E. faecalis (139), E. faecium (41), E. casseliflavus (5), E. gallinarum (3), E. avium (2) and E. hirae (1). The percent- ages of antibiotic resistance detected were as follows (E. faecalis/ E. faecium/ other species) : penicillin (0/ 73/ 9%), tetracycline (78/ 44/ 54%), chloramphenicol (52/ 29/ 27%), erythromycin (66/ 100/ 82%), spiramycin (84/ 83/ 64%), pristi- namycin (100/ 0/ 73%), trimethoprim-sulfamethoxazole (88/ 78/ 91%), rifampicin (72/ 41/ 0%), vancomycin (0/ 0/ 36%), teicoplanin (0/ 0/ 0%), high-level-resis- tance for gentamicin (24/ 29/ 45%), streptomycin (34/ 56/ 55%) and kanamycin (41/ 68/ 55%). Increased vancomycin minimum inhibitory concentrations (MICs) were only detected in E. casseliflavus and E. gallinarum isolates (MIC range 8-24 μg/ml). The erm(B), catA, tet(M), aac(6´)-aph(2´´), aph(3´)-IIIa, and ant(6)-Ia genes were detected in 91%, 32%, 86%, 98%, 100%, and 72% of the E. faecium and E. faecalis isolates resistant to erythromycin, chloramphenicol, tetracycline and high- level-resistant to gentamicin, kanamycin and streptomycin, respectively. A total of 20 unrelated pulsed-field-gel-electrophoresis patterns were found in the series of 46 high-level gentamicin-resistant E. faecalis and E. faecium isolates of this study. Key words : Enterococci, Tunisia, antibiotic resistance, resistance genes. REVIEW copy for private use only