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

Abstract

BackgroundThe 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.MethodsSeventy-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.ResultsThe 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%.ConclusionsWe established optimal mCIM conditions for simple, accurate, and reproducible detection of carbapenemase-producing A. baumannii.

Molecular Characterisation of Carbapenemase-Producing Acinetobacter baumannii isolates from Hospitalised Patients in Iraq

“…This indicate that this method is more sensitive than other phenotypic approaches. Our finding was in agreement with previous studies in Iraq (100%) (Al Meani et al, 2020), and Kuria (100%) (Vu et al, 2020).…”

A Variant Carbapenem Inactivation Method (CIM) for Acinetobacter baumannii Group with Shortened Time-to-Result: rCIM-A

“…As smaller volumes were shown to reduce sensitivity at better specificity in Acinetobacter too much [66,67,75], the volume contained in a 10 µL inoculation loop was used for preparing a suspension in 400 µL TSB containing 0.1% (vol/vol) Triton TM X-100. The mildly membrane-permeabilizing 0.1% (vol/vol) Triton TM X-100 [67,71] plus TSB (carbapenem-protective, [68]) approach was chosen, since the disk incubation step in watersuspension [62] or TSB [66] did not result in sufficient bacterial-borne lytic activity [62] and Tris-HCl extraction was shown to degrade the carbapenem unspecifically [69].…”

“…Because of the lack of accurate and rapid phenotypic methods for carbapenemase detection in Acinetobacter, variations of the classical CIM method [62] have been tested [64,[66][67][68][69][70][71]. Performance characteristics of which are summarized in Table 1.…”

Comparative study of phenotypic-based detection assays for carbapenemase-producing Acinetobacter baumannii with a proposed algorithm in resource-limited settings

“…Many attempts have been made to increase the sensitivity and specificity of this test for A . baumannii by applying additional reagents such as Tris-HCl and Triton-X [ 31 , 32 ]. sCIM was proposed in 2018 with a procedure adapted from mCIM, which exhibited promising results for A .…”

“…As also observed in our study, mCIM showed lower than 40% sensitivity to detect carbapenemase-producing A. baumannii. Many attempts have been made to increase the sensitivity and specificity of this test for A. baumannii by applying additional reagents such as Tris-HCl and Triton-X [31,32]. sCIM was proposed in 2018 with a procedure adapted from mCIM, which exhibited promising results for A. baumannii detection with 100% accuracy [19].…”