Multicenter Study to Assess the in vitro Activity of Tigecycline by Disk Diffusion Test against Clinical Isolates from Argentina

Background: Tigecycline is a new antibiotic currently used in healthcare environments where multidrug resistance is prominent. Because there is a constant potential for resistance to emerge, survey studies are needed. Methods: Isolates collected in 20 clinical laboratories from 4 states of Argentina between November 2005 and October 2006 were tested using the disk diffusion method as described by the CLSI. Results: A total of 3,182 isolates were assessed. Gram-positive cocci represented 43.4% of the total isolates [Staphylococcus aureus (878), coagulase-negative staphylococci (255), Enterococcus spp. (201), Streptococcus spp. (47)], Enterobacteriaceae 39.6% and Acinetobacter spp. 11.1%. Tigecycline proved equally active against methicillin-resistant and methicillin-susceptible staphylococci, as well as against vancomycin-resistant and vancomycin-susceptible enterococci (100% of susceptibility for all Gram-positive bacteria tested). Tigecycline susceptibility for Enterobacteriaceae, other than Proteeaetribe and Serratia spp., ranged from 88 to 100%, including against strains with resistance to third-generation cephalosporins with phenotype of extended spectrum β-lactamases (extended spectrum β-lactamase-positive Escherichia coli 17.7% and extended spectrum β-lactamase-positive Klebsiella pneumoniae 50.5%). Adopting a resistant breakpoint of 16 mm, 92% of the Acinetobacter isolates were susceptible to tigecycline. Conclusion(s): Tigecycline was active against a wide variety of bacterial species, including most of the multidrug-resistant Gram-negative and Gram-positive bacteria. Therefore, it could be a suitable option in the treatment of infections caused by these organisms in hospitalized patients.