Comparative activity of tigecycline and tetracycline on Gram-negative and Gram-positive bacteria revealed by a multicentre study in four North European countries

Abstract

Background: This study involves a multicentre surveillance of tigecycline and tetracycline activity against Gram-negative and Gram-positive bacteria from primary care centres (PCCs), general hospital wards (GHWs) and intensive care units (ICUs) in Denmark (n = 9), Finland (n = 10), Norway (n = 7) and Sweden (n = 19).

Methods: The hospitals were each asked to test 30 consecutive Gram-positive and 30 Gram-negative clinical isolates. Supportive information accompanying each isolate included the study centre, ward level (PCC, GHW, or ICU), patient identification and source of the isolate. Minimum inhibitory concentrations (MICs) for tetracycline and tigecycline were determined with the Etest.

Results: The isolates collected comprised 1610 Gram-negative and 1767 Gram-positive clinical isolates. The study showed low rates of non-susceptibility (intermediate (I) and resistant (R)) to tigecycline: <1% in Escherichia coli, though other Enterobacteriaceae showed higher rates (Enterobacter cloacae (7%), Klebsiella pneumoniae (9%) and Serratia spp. (23%)). The overall non-susceptibility rate for tigecycline in Enterobacteriaceae with species-related breakpoints for tigecycline was 6% (4% excluding Serratia spp.). The activity of tigecycline against Haemophilus influenzae and Acinetobacter spp. was high with a MIC(50) of 0.25 mg/l and MIC(90) of 1 mg/l. The prevalence of non-susceptibility to tigecycline among Gram-positive bacteria was <1%. The corresponding figure for tetracycline was 14%. The activity of tigecycline against Streptococcus pneumoniae was high with MIC(50) and MIC(90) of 0.125 mg/l.

Conclusion: Tigecycline showed good overall in vitro activity against Gram-positive and Gram-negative isolates, including both tetracycline-susceptible and resistant isolates. Most non-susceptibility to tigecycline among Enterobacteriaceae other than E. coli was I (6%), rather than R (<1%). This indicates a problem setting interpretive species-related tigecycline breakpoints for Enterobacteriaceae other than E. coli.