Abstract

ABSTRACT Tigecycline is a broad-spectrum glycylcycline antibiotic with activity against not only susceptible gram-positive and gram-negative pathogens but also strains that are resistant to many other antibiotics. In the process of determining quality control (QC) limits for the American Type Culture Collection reference strains for tigecycline, a number of inconsistencies in MICs were encountered which appeared to be related to the age of the Mueller-Hinton broth (MHB) medium used in the MIC testing. The objective of this study was to determine the cause of the discrepant MIC results between fresh and aged MHB. The MICs of tigecycline were determined in MHB that was either prepared fresh (<12 h old), prepared and stored at 4°C, stored at room temperature, stored anaerobically, or supplemented with the biocatalytic oxygen-reducing reagent Oxyrase. When tested in fresh media, tigecycline was 2 to 3 dilutions more active against the CLSI-recommended QC strains compared to aged media (MICs of 0.03 to 0.25 and 0.12 to 0.5 μg/ml, respectively). Media aged under anaerobic conditions prior to testing or supplemented with Oxyrase resulted in MICs similar to those obtained in fresh medium (MICs of 0.03 to 0.12 and 0.03 to 0.25 μg/ml, respectively). Time-kill kinetics demonstrated a >3 log 10 difference in viable growth when tigecycline was tested in fresh or Oxyrase-supplemented MHB compared to aged MHB. High-pressure liquid chromatography analysis revealed the accumulation of an early peak (oxidative by-product of tigecycline) to be 3.5% in fresh media and 25.1% in aged media after 24 h and that addition of Oxyrase prevented the accumulation of this oxidized by-product. These results suggested that the activity of tigecycline was affected by the amount of dissolved oxygen in the media. The use of fresh MHB or supplementation with Oxyrase resulted in a more standardized test method for performing MIC tests with tigecycline.

Keywords

TigecyclineMicrobiologySerial dilutionBiologyFood scienceAntibioticsAntimicrobialMedicine

MeSH Terms

BacteriaChromatographyHigh Pressure LiquidCulture MediaEnterococcus faecalisEscherichia coliMicrobial Sensitivity TestsMinocyclineOxygenasesReducing AgentsStaphylococcus aureusTigecycline

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Publication Info

Year
2005
Type
article
Volume
49
Issue
9
Pages
3903-3909
Citations
110
Access
Closed

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Cite This

Patricia A. Bradford, Peter J. Petersen, Mairead Young et al. (2005). Tigecycline MIC Testing by Broth Dilution Requires Use of Fresh Medium or Addition of the Biocatalytic Oxygen-Reducing Reagent Oxyrase To Standardize the Test Method. Antimicrobial Agents and Chemotherapy , 49 (9) , 3903-3909. https://doi.org/10.1128/aac.49.9.3903-3909.2005

Identifiers

DOI
10.1128/aac.49.9.3903-3909.2005
PMID
16127069
PMCID
PMC1195415

Data Quality

Data completeness: 86%