Detection of SPM-1-producing Pseudomonas aeruginosa and class D β-lactamase-producing Acinetobacter baumannii isolates by use of liquid chromatography-mass spectrometry and matrix-assisted laser desorption ionization-time of flight mass spectrometry

Abstract

This study evaluates the accuracy of liquid chromatography-mass spectrometry (LC-MS) and matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF) for detecting carbapenem hydrolytic activity among SPM-1-, GIM-1-, and GES-5-producing Pseudomonas aeruginosa isolates and OXA-143-, IMP-10-, and OXA-58-producing Acinetobacter baumannii isolates. Class A and B carbapenemase activities were rapidly detected by MALDI-TOF in a 2-h assay. However, an extended incubation time was necessary for detection of carbapenem-hydrolyzing class D β-lactamase (CHDL) activity in Acinetobacter spp.

Fig 1

(A) The hydrolysis of ETP mediated by β-lactamases occurs in two steps: in the first step, the ETP intact molecule (475 g mol⁻¹) suffers a rupture on its β-lactam ring, resulting in a hydrolyzed ETP molecule (493 g mol⁻¹). In the second step, the hydrolyzed ETP molecule loses a carboxyl group (−CO₂), resulting in a metabolite with a molecular mass of 450 g mol⁻¹ (hydrolyzed and decarboxylated ETP molecule). (B) Analysis of ETP degradation by MALDI-TOF MS. (B1) Results for a negative-control strain incubated with ETP solution which appears ionized with hydrogen ([ETP + H]⁺ = 475 g mol⁻¹) and its sodium adduct ([ETP + Na]⁺ = 497 g mol⁻¹). (B2) Results for a hydrolyzed and decarboxylated ETP after incubation with SPM-1-producing P. aeruginosa. Arrows represent HCCA matrix peaks. (C) Analysis of ETP degradation by LC-MS. (C1) Results for a negative-control strain incubated with ETP which appears ionized with hydrogen ([EPT + H]⁺ = 476 g mol⁻¹). (C2) Hydrolyzed and decarboxylated ETP after incubation with SPM-1-producing P. aeruginosa ([ETP + H]⁺ = 450 g mol⁻¹).