Comparative In Vitro Activity of Tigecycline and Nine Other Antibiotics Against Gram-Negative Bacterial Isolates, Including ESBL-Producing Strains

The Enterobacteriaceae, especially Escherichia coli and Klebsiella spp., as well as Acinetobacter spp., are important agents of nosocomial infections in hospitalized patients. A total of 460 Gram-negative bacteria (GNB), were investigated for their susceptibility to tigecycline and 9 other antibiotics by the Etest. ESBL production was inferred from ESBL Etest phenotypes. All the GNB, including the ESBL-producers, were susceptible to tigecycline with MIC90 ranges of 0.25 to 2 mu g/ml. Imipenem and meropenem were very active against ESBL and non-ESBL producers; mean MIC(90)s of 0.19 and 0.09 mu g/ml and 0.05 mu g/ml and 0.02 mu g/ml, respectively. The MIC(90)s of imipenem and meropenem for the Acinetobacter spp. were 16 and >32 mu g/ml, respectively with resistance rates of 64.3 and 66.1%. ESBL production was detected in 62% and 82.1% of the E. coli and K. pneumoniae isolates, respectively. Resistance to ciprofloxacin was higher among the ESBL-producing strains of E. coli and K. pneumoniae than the non-ESBL producers. Comparatively, tigecycline had excellent in vitro activities against ESBL-producing Enterobacteriaceae and demonstrated superior activity against Acinetobacter spp. Increasing ESBL production and resistance to ciprofloxacin and gentamicin in Enterobacteriaceae require careful selection of empirical therapy. Tigecycline holds promise as an alternative choice of therapy for infections caused by ESBL-producing isolates and multi-drug resistant Acinetobacter spp. Key words: Tigecycline, susceptibility, Gram-negative bacteria, ESBL-producing bacteria.