cThe emergence of carbapenemase-producing bacteria poses a new challenge in the management of antibiotic therapies for patients. This report describes a new method using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) for rapid detection of carbapenemase activity in enterobacteria, Pseudomonas aeruginosa, and Acinetobacter baumannii. In a panel of 78 isolates, including 41 carbapenemase-producing strains, the ULPC-MS/MS assay showed 100% agreement with molecular characterization, whereas six carbapenemase-producing isolates were not detected by the modified Hodge test.T he emergence and dissemination of resistance to carbapenem in Gram-negative pathogens such as Enterobacteriaceae, Acinetobacter baumannii, and Pseudomonas aeruginosa represent a challenge for optimizing antibiotic therapies and preventing outbreaks, especially regarding carbapenemase-producing bacteria, by comparison to other resistance mechanisms. Using the Ambler classification of beta-lactamases, the principal carbapenemase enzymes detected in infected patients worldwide belong to class B (metallo-beta-lactamases, including IMP, VIM, and NDM), to class A (beta-lactamases, including Klebsiella pneumoniae carbapenemase [KPC]), and to class D (oxacillinases, including OXA-48 and OXA-23). Moreover, clinical infections due to these carbapenemase-producing strains, which are also resistant to most betalactam antibiotics, are associated with higher morbidity and mortality (1). Bacterial resistance to carbapenem is usually screened using susceptibility and phenotypic assays such as the modified Hodge test (MHT) (2). However, these tests have shown poor sensitivity and specificity in detecting carbapenemase-producing isolates, especially in A. baumannii (3). While PCR-based detection of the carbapenemase gene is considered the gold standard method, in view of the high genetic diversity of genes coding for carbapenemase, numerous PCR assays targeting the most prevalent enzymes must be developed in this approach (2, 4). Recently, mass spectrometry (MS) technologies, such as matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) and ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS), have been shown to be capable of characterizing carbapenemase-producing bacteria (5,6,7,8).This study reports on a rapid UPLC-MS/MS assay to detect carbapenemase-producing Enterobacteriaceae, P. aeruginosa, and A. baumannii isolates based on the ability of bacterial isolates to hydrolyze ertapenem and meropenem in solution.A total of 78 bacterial strains (27 reference strains and 51 strains isolated from clinical samples) were included in the study: 41 carbapenemase-producing strains (including 23 enterobacterial strains, 3 P. aeruginosa strains, and 15 A. baumannii strains) and 37 strains susceptible to carbapenems or harboring decreased susceptibility to carbapenems due to non-carbapenemase-based mechanisms. Escherichia coli ATCC 25922 and Citrobacter freundii NDM-1-positive strain...

Background Preoperative decolonization is recommended in Staphylococcus aureus nasal carriers scheduled for cardiac surgery. We aimed to evaluate the effectiveness of and compliance with mupirocin use in nasal S. aureus carriers in a real-life setting. Methods Prospective study including consecutive patients scheduled for cardiac surgery screened for S. aureus nasal carriage at preoperative consultation. Carriers were prescribed mupirocin nasal ointment, chlorhexidine shower and mouthwash. Effectiveness of decolonization was evaluated with a postoperative nasal sample. Compliance was evaluated objectively by determination of nasal mupirocin concentration using UPLC-MS/MS and self-reported by questionnaire. Results Over 10 months, 361 patients were included, 286 had preoperative screening, 75 (26.2%) were S. aureus nasal carriers and 19 of them (25.3%) failed to be effectively decolonized. No resistance to mupirocin was documented. Preoperative and postoperative strains were identical in all cases. Declared good compliance was associated with decolonization success (OR = 24; 95% CI 4–143, P < 0.0001). Mupirocin detection was significantly associated with the level of compliance. Mupirocin was detected in 52.2% (24/46) of patients effectively decolonized and in 12.5% (2/16) of patients with decolonization failure (P < 0.01). In 2/19 patients, failure of decolonization was not associated with a compliance issue. Postoperative carriage was associated with an increased risk of S. aureus infection (OR = 9.8; 95% CI 1.8–53, P < 0.01). Conclusions In real life, decolonization is not always effective, hence there is a persisting risk of S. aureus endogenous infection. Mupirocin concentration measurement may help to understand compliance issues and failures in decolonization.