[Variability in the sensitivity to tigecycline against Acinetobacter baumannii in different culture media]
A Tenorio-Abreu1, J M Eiros, E Rodríguez-Molins
1Servicio de Microbiología, Hospital Clínico Universitario de Valladolid, Avda. Ramón y Cajal 3, 47005 Valladolid, Spain. atenabr@gobiernodecanarias.org
Introduction:
The tigecycline may represent a therapeutic alternative for the control of multiresistant A. baumannii, although there is no consensus regarding the cutoff points for sensitivity or variability of MIC as a function of culture medium used for the antibiogram against this microorganism. Therefore, our objective was to verify this variability, and propose the culture medium that comes closest to the standard method.
Methods:
We selected 41 strains of carbapenem-resistant A. baumannii. We analyzed the sensitivity to tigecycline in different culture media: Mueller Hinton agar Oxoid commercial (C-MH), Mueller Hinton fresh agar BD and Co., USA (F-MH) and ISO-sensitest fresh agar Oxoid, using the E-test and disk. The MICs were compared against those obtained using the technique standard of macrodilution.
Results:
The mean MIC and inhibition diameters obtained in the different culture media corresponded to 9.26 mg/L and 15.1 mm in diameter for MH-C, 1.71 mg/L and 22.7 mm for MH-F; 2.68 mg/L and 20.8 mm for ISO-sensitest. Half the MIC obtained by the standard method of dilution was 0.47 mg/L (SD =0.21), with values between 0.25 and 1 mg/L.
Conclusion:
In the three growth media studied, MICs superior to the standard are observed, which is false to interpret resistance in many cases. However, the medium that comes closer more that of reference is the MH-F.
