In vitro Activity of Tigecycline Against Clinical Isolates of Gram-Positive and Gram-Negative Bacteria Displaying Different Resistance Phenotypes

Objectives. The aim of the study was to evaluate the in vitro activity of tigecycline against clinically relevant isolates of Gram-positive and Gram-negative bacteria resistant to different antimicrobial drugs. Material and Methods. A total of 495 clinical isolates, including methicillin-resistant Staphylococcus aureus (MRSA) (n = 19), methicillin-resistant coagulase-negative Staphylococcus spp. (MRCNS) (n = 56), methicillinsusceptible Staphylococcus aureus resistant to tetracycline (MSSA T-R) (n = 113), high- level aminoglycoside-resistant (HLAR) Enterococcus spp. (n = 181), and extended-spectrum beta-lactamase (ESBL)-producing bacilli (n = 126), were used in this study. The clinical isolates were obtained from patients hospitalized at the Medical University Hospital in Wroclaw, Poland, during a three-year period (2005-2007). The minimal inhibitory concentrations (MICs) of tigecycline for the strains were determined by the agar dilution technique on Mueller-Hinton agar. Results. Tigecycline exhibited excellent activity against all Gram-positive cocci tested, with MIC90 values ranging from 0.03 to 0.06 mg/L. In addition, this antimicrobial was also very potent against all ESBL-producing strains tested with an MIC90 of 0.25 mg/L. The activity of tigecycline against ESBL-producers was comparable to that of imipenem. Conclusions. Tigecycline could be considered an alternative antibacterial agent for the treatment of serious infections caused by drug-resistant bacterial strains (Adv Clin Exp Med 2008, 17, 5, 545-551).