Abstract
Colistin is frequently a last resort treatment for Pseudomonas aeruginosa infections caused by multidrug-resistant (MDR) and extensively drug resistant (XDR) strains, and detection of colistin resistance is essential for the management of infected patients. Therefore, we evaluated the recently developed MALDIxin test for the detection of colistin resistance in P. aeruginosa clinical strains using the routine matrix-assisted laser desorption ionization (MALDI) Biotyper Sirius system. The test is based on the detection by mass spectrometry of modified lipid A by the addition of 4-amino-l-arabinose (l-ara4N) molecules on one or two phosphate groups, in strains resistant to colistin. Overproduction of l-Ara4N molecules is mainly due to the constitutive activation of the histidine kinase (PmrB) or the response regulator (PmrA) following an amino-acid substitution in clinical strains. The performance of the test was determined on a panel of 14 colistin-susceptible and 14 colistin-resistant P. aeruginosa clinical strains, the reference strain PAO1 and positive control mutants PmrB (V28G), PmrB (D172), PhoQ (D240–247), and ParR (M59I). In comparison with the broth microdilution (BMD) method, all the susceptible strains (n=14) and 8/14 colistin-resistant strains were detected in less than 1h, directly on whole bacteria. The remaining resistant strains (n=6) were all detected after a short pre-exposure (4h) to colistin before sample preparation. Validation of the method on a larger panel of strains will be the next step before its use in diagnostics laboratories. Our data showed that the MALDIxin test offers rapid and efficient detection of colistin resistant P. aeruginosa and is thus a valuable diagnostics tool to control the spread of these emerging resistant strains.
Highlights
Pseudomonas aeruginosa is an opportunistic pathogen well-known for infections associated with intensive care units
The aim of this study is to evaluate the performance of the optimized MALDIxin test using a routine matrix-assisted laser desorption ionization (MALDI) mass spectrometer, to detect colistin-resistant P. aeruginosa
To assess the ability of the MALDIxin test to detect colistinresistance in P. aeruginosa on a MALDI biotyper Sirius system, we tested a panel of 33 P. aeruginosa strains, including four isogenic P. aeruginosa PAO1 mutants representing the most frequently mutated genes involved in colistin resistance in this species
Summary
Pseudomonas aeruginosa is an opportunistic pathogen well-known for infections associated with intensive care units. It is one of the most frequent cause of acute pulmonary healthcare-associated infections, and severe infections in immunocompromised patients (Vincent et al, 2009). In P. aeruginosa, acquired resistance to colistin mostly results from the addition of one or two 4-amino-l-arabinose (l-Ara4N) molecules to the 1 and/or 4' phosphate groups on the lipid A, the anchor of the LPS in the outer membrane (Bhat et al, 1990; Fernandez et al, 2013). In P. aeruginosa clinical strains, the genetic events most associated with colistin resistance are amino-acid substitutions leading to a gain of function of the PmrB protein (Barrow and Kwon, 2009; Schurek et al, 2009; Bolard et al, 2019). The mcr genes have been widely reported in Enterobacterales, they have not currently been identified in P. aeruginosa strains, except in the chromosome of one clinical isolate strain (mcr-5; Snesrud et al, 2018)
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