Antimicrobial Activity of Tigecycline Tested against Contemporary Bacterial Isolates Collected in Australia (2006)

Background: Tigecycline has been marketed in Australia for over one year. As part of the SENTRY Antimicrobial Surveillance Program (Asia-Pacific Region), we evaluated the activity of tigecycline against recent (2006) bacterial isolates across Australia. Methods: Non-duplicate strains were consecutively collected from five medical centres in 5 states using isolates from bacteraemia (n=253), pneumonia (n=146), complicated skin and skin structure infections (n=264), and other infections (n=269). All isolates were tested against tigecycline using validated commercial reference broth microdilution panels (TREK Diagnostics), with concurrent quality controls and CLSI (M100-S18) interpretations for comparison agents. Tigecycline breakpoints published by the USFDA were applied for each indicated species or genus group. results: A total of 932 (268 Gram-negative and 664 Gram-positive) isolates were processed. Tigecycline was highly active against the top 10 non-pseudomonal pathogens which comprised 88% of all tested isolates (see Table). Tigecycline MIC90 results ranged from ≤0.12 to 1 mg/L, highest for Klebsiella spp. and Proteae (data not shown). At US-FDA published breakpoints, tigecycline exhibited complete inhibition of indicated species except for a single strain of E. cloacae (MIC, 4 mg/L). Over 28% of Staphylococcus aureus were oxacillin-resistant, and one Enterococcus faecium was vancomycin-resistant. Tigecycline was highly effective against these strains. Conclusions: Tigecycline has potent activity against all the common pathogens isolated in 2006 from Australian patients, including those resistant to other drug classes. Documented acquired resistance was rare among indicated pathogens, however, Pseudomonas remains refractory to potential tigecycline therapy.