Use of MALDI-TOF VITEK MS for rapid and efficient identification of KPC-type carbapenemases in Enterobacterales carrying the Tn4401a transposon.

PURPOSE

To determine diagnostic validity of MALDI-TOF MS (VITEK MS) system for detecting Klebsiella pneumoniae carbapenemases (KPC)-type carbapenemases by identifying the 11,109 Da peak in the mass spectrum generated for species identification as compared to RAPIDEC CARBA NP, and the modified carbapenemase inactivation method (mCIM) and the EDTA-modified carbapenem inactivation method (eCIM) in a collection of isolates previously characterized as KPC positive or negative.

METHODS

210 Enterobacterales clinical strains previously characterized having bla gene, the pKpQIL plasmid and the Tn4401a transposon were evaluated, including 34 positive controls carbapenemase-producing Klebsiella pneumoniae associated with Tn4401a, 30 Enterobacterales bla positive of unknown plasmid background, and 146 negative controls. Accuracy and agreement were established for Vitek MS, RAPIDEC CARBA NP, and mCIM/eCIM) tests; ROC curves were compared among these tests.

RESULTS

The 11,109 Da peak was detected in 100% of KPC Tn4401a positive isolates using Vitek MS, sensitivity of 100% (95% CI 98.53-100), specificity of 95.5% (95% CI 91.7-99.4), positive predictive value (PPV) of 85.0 (95% CI 72.7-97.3), negative predictive value (NPV) of 100% (95% CI 99.6-100) and positive Likelihood Ratio (PLR) of 22.3 (10.2-48.8). Agreement between the three tests was 93.3% Kappa index of 0.90 (95% CI 0.83-0.97, p ≤ 0.05). ROC curves showed areas under the curve (AUCs) of 0.95, 0.96 and 0.96 for the VITEK MS, RAPIDEC CARBA NP and the mCIM/eCIM tests, respectively.

CONCLUSION

Detection of the 11,109 Da peak by Vitek MS confirms the presence of KPC-type carbapenemase, allowing rapid and simultaneous detection with species identification; a negative result does not rule out the presence of the enzyme and may require additional tests.