A rapid MALDI-TOF mass spectrometry-based method for categorization of Pseudomonas aeruginosa from blood cultures as susceptible or resistant to meropenem.

We developed and evaluated a simple, low-cost matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF MS)-based method for the detection of meropenem (MER) resistance in Pseudomonas aeruginosa directly from blood. A volume of 50 μL of positive-flagged blood culture (BC) was transferred in 450 μL brain heart infusion (BHI) broth to microtubes either containing MER (test) or not (control) at 25 or 50 mg/L. P. aeruginosa was categorized as resistant or susceptible on the basis of whether or not the isolates could be identified, respectively, in the presence of the antibiotic (3 h of incubation). When using BCs spiked with 99 P. aeruginosa isolates (64 MER-resistant and 35 MER-susceptible) the method correctly classified 88/99 isolates (88.9%). Correct categorization was achieved in 23/23 (100%) of P. aeruginosa isolates (17 MER-susceptible and 6 MER-resistant) from prospectively collected BCs. Our method may prove useful for early targeted or adjustment of empirical therapy in patients with P. aeruginosa bloodstream infections.