Ann Lab Med.  2020 Jan;40(1):21-26. 10.3343/alm.2020.40.1.21.

Adjustment of Modified Carbapenem Inactivation Method Conditions for Rapid Detection of Carbapenemase-Producing Acinetobacter baumannii

• Vu TN
• Byun JH
• D'Souza R
• Pinto NA
• Nguyen LP
• Yong D
• Chong Y

• KMID: 2457489
• DOI: http://doi.org/10.3343/alm.2020.40.1.21

Abstract

BACKGROUND
The existing modified carbapenem inactivation methods (mCIMs) recommended by the CLSI for detecting carbapenemase production have not been applicable for Acinetobacter baumannii. We evaluated the influence of matrices used in mCIMs and CIMTris on the stability of the disks for detecting carbapenemase producers and suggested optimal mCIM conditions for detecting carbapenemase-producing A. baumannii.
METHODS
Seventy-three A. baumannii isolates characterized for antimicrobial susceptibility and carbapenemase encoding genes were tested for carbapenemase production using mCIM and CIMTris. The influence of the matrices (Tryptic soy broth [TSB] and Tris-HCl) used in these methods on the stability of the meropenem (MEM) disk was also evaluated. The mCIM conditions were adjusted to enhance screening sensitivity and specificity for detecting carbapenemase-producing A. baumannii.
RESULTS
The matrices had an impact on the stability of the MEM disk after the incubation period (two or four hrs). TSB nutrient broth is an appropriate matrix for mCIM compared with Tris-HCl pH 7.6, which leads to the loss of MEM activity in CIMTris. The sensitivity and the specificity of the optimal mCIM were both 100%.
CONCLUSIONS
We established optimal mCIM conditions for simple, accurate, and reproducible detection of carbapenemase-producing A. baumannii.

Keyword

Carbapenemase; Acinetobacter baumannii; Modified carbapenem inactivation method; CIMTris

MeSH Terms

Acinetobacter baumannii*
Acinetobacter*
Hydrogen-Ion Concentration
Mass Screening
Methods*
Sensitivity and Specificity

Figure

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  Fig. 1 (A) Schematic drawing of remaining potency of MEM disks in two types of buffers (TSB and Tris-HCl) after two or four hours of incubation. Diameter of inhibition zone with (B, C) incubated MEM disk depending on type and volume of matrix and duration of incubation, (D, E) MEM dissolved in TSB or Tris-HCl buffer. Tris-HCl weakened MEM potency, which was not maintained in either the buffer or disk.Abbreviations: MEM, meropenem; TSB, tryptic soy broth.

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