Optimization of the MALDIxin test for the rapid identification of colistin resistance in Klebsiella pneumoniae using MALDI-TOF MS.

Background: With the dissemination of carbapenemase producers, a revival of coListin was observed for the treatment of infections caused by MDR Gram-negatives. UnfortunateLy, the increasing usage of coListin Led to the emergence of resistance. In Klebsiella pneumoniae, coListin resistance arises through addition of 4-amino-L-arabinose (L-Ara4N) or phosphoethanolamine (pEtN) to the native Lipid A. The underlying mechanisms involve numerous chromosome-encoded genes or the pLasmid-encoded pEtN transferase MCR. Currently, detection of coListin resistance is time-consuming since it stiLL relies on MIC determination by broth microdiLution. Recently, a rapid diagnostic test based on MALDI-TOF MS detection of modified Lipid A was developed (the MALDIxin test) and tested on Escherichia coli and Acinetobacter baumannii. Objectives: Optimize the MALDIxin test for the rapid detection of coListin resistance in K. pneumoniae. Methods: This optimization consists of an additional mild-acid hydrolysis of 15 min in 1% acetic acid. The optimized method was tested on a coLLection of 81 cLinicaL K. pneumoniae isolates, including 49 coListin-resistant isoLates (45 with chromosome-encoded resistance, 3 with MCR-reLated resistance and 1 with both mechanisms). Results: The optimized method afiowed the rapid (<30 min) identification of L-Ara4N- and pEtN-modified Lipid A of K. pneumoniae, which are known to be the red triggers of poLymyxin resistance. At the same time, it discriminates between chromosome-encoded and MCR-reLated poLymyxin resistance. Conclusions: The MALDIxin test has the potential to become an accurate tool for the rapid determination of coListin resistance in cLinicaLLy relevant Gram-negative bacteria.