Rapid detection of colistin resistance in Acinetobacter baumannii using MALDI-TOF-based lipidomics on intact bacteria

With the dissemination of extremely drug resistant bacteria, colistin is now considered as the lastresort therapy for the treatment of infection caused by Gram-negative bacilli (including carbapenemase producers). Unfortunately, the increase use of colistin has resulted in the emergence of resistance as well. In A. baumannii, colistin resistance is mostly caused by the addition of phosphoethanolamine to the lipid A through the action of a phosphoethanolamine transferase chromosomally-encoded by the pmrC gene, which is regulated by the two-component system PmrA/PmrB. In A. baumannii clinical isolate the main resistance mechanism to colistin involves mutations in pmrA, pmrB or pmrC genes leading to the overexpression of pmrC. Although, rapid detection of resistance is one of the key issues to improve the treatment of infected patient, detection of colistin resistance in A. baumannii still relies on MIC determination through microdilution, which is time-consuming (16-24 h). Here, we evaluated the performance of a recently described MALDI-TOF-based assay, the MALDIxin test, which allows the rapid detection of colistin resistance-related modifications to lipid A (i.e phosphoethanolamine addition). This test accurately detected all colistin-resistant A. baumannii isolates in less than 15 minutes, directly on intact bacteria with a very limited sample preparation prior MALDI-TOF analysis.