A Nordic study exploring the activity of tigecycline against tetracycline-resistant Gram-positive and Gram-negative bacteria

Abstract number: p1323

Nilsson  L.E., Koernig  T., Frimodt Møller  N., Skov Simonsen  G., Vaara  M.

Objectives: 

Tigecycline is a glycylcycline developed as a parenteral extended-spectrum agent. This study shows the activity of tigecycline against tetracycline resistant isolates of Gram-positive and Gram-negative bacteria isolated in four Nordic countries.

Methods: 

A total of 1641 Gram-positive isolates and 1660 gram-negative isolates were collected from hospital laboratories in Denmark (n = 9), Finland (n = 11), Norway (n = 12) and Sweden (n = 24) during 2005. Susceptibility testing was performed with Etest using FDA breakpoints for tigecycline (Staphylococci S <= 0.5 mg/l, Streptococci except S. pneumoniae S <= 0.25, E. faecalis S <= 0.25, enterobacteriacae S <= 2 mg/l) and the Swedish Reference Group for Antibiotics (SRGA) breakpoints for tetracycline (R > 2 mg/l). A total of 457 tetracycline resistant Gram-positive isolates and 821 tetracycline resistant gram-negative isolates were evaluated.

Results: 

Activity of tigecycline is summarized in the table. The susceptibility was high against all species with FDA-breakpoints except for P. mirabilis and M. morganii. The other species showed a high tigecycline susceptibility >=90% for tetracycline resistant isolates. For tetracycline resistant isolates tigecycline MIC50 increased 2-fold for CoNS, Acinetobacter spp and H. influenzae and MIC90 increased 2-fold for S. aureus, S. pyogenes, K. pneumoniae, M. morganii and Acinetobacter spp

Conclusion: 

Tigecycline remained highly active against most tetracycline resistant isolates, probably due to stability to the commonly occurring tetracycline resistant mechanisms in Gram-positive and Gram-negative bacteria.