title: Investigation of tigecycline bactericidal activity: Optimisation of laboratory testing.
abstract: The objectives of this study were to optimise the conditions for bactericidal testing of tigecycline and to investigate its bactericidal activity against clinical isolates of Gram-positive and Gram-negative bacteria. Tigecycline is the first in a new class of glycylcycline antibiotics exhibiting in vitro activity against a broad range of bacteria, including multidrug-resistant organisms. Its bactericidal activity in vitro has not been extensively investigated using multiple test conditions. Five growth media comprising Mueller Hinton broth, Minimum Essential Medium of Eagle, Ham F-12, RPMI 1640 and Iso-Sensitest broth (ISB) with and without surfactant (Tween 80) were investigated in vitro to assess tigecycline bactericidal activity. Clinical isolates of meticillin-resistant Staphylococcus aureus, meticillin-susceptible S. aureus, Escherichia coli, Klebsiella pneumoniae and Enterococcus spp., representing the majority of clinically relevant bacteria, were evaluated for the impact of test conditions on the tigecycline minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC), ISB with 0.02% Tween 80 most efficiently demonstrated the bactericidal action of tigecycline when evaluated in 64 well-characterised clinical isolates and was considered as the optimal bactericidal test medium. Using this condition, tigecycline approached 56% bactericidal activity with 3log10reduction in CFUs at 72h incubation. Bactericidal action increased to 80% of strains when 2log10reduction was used as the endpoint. Only Enterococcus spp. showed no bactericidal response in this analysis. Tigecycline exhibited a bactericidal effect in vitro against Gram-positive and Gram-negative bacteria. At the tested in vitro conditions, tigecycline MICs were unchanged regardless of the different test media used.
authors.affiliation: Infectious Disease Research, NorthShore University HealthSystem, 2650 Ridge Ave., Evanston, IL 60201, USA; University of Chicago Pritzker School of Medicine, Chicago, IL, USA. Electronic address: EUsacheva@northshore.org.
authors.forename: Elena A
authors.initials: EA
authors.lastname: Usacheva
authors.affiliation: Infectious Disease Research, NorthShore University HealthSystem, 2650 Ridge Ave., Evanston, IL 60201, USA.
authors.forename: Althea
authors.initials: A
authors.lastname: Grayes
authors.affiliation: Infectious Disease Research, NorthShore University HealthSystem, 2650 Ridge Ave., Evanston, IL 60201, USA.
authors.forename: Donna
authors.initials: D
authors.lastname: Schora
authors.affiliation: Infectious Disease Research, NorthShore University HealthSystem, 2650 Ridge Ave., Evanston, IL 60201, USA; University of Chicago Pritzker School of Medicine, Chicago, IL, USA.
authors.forename: Lance R
authors.initials: LR
authors.lastname: Peterson
keywords: Bactericidal activity; Growth media; MBC; MIC; Tigecycline