Significance and Impact of the Study: MALDI-TOF mass spectrometry is increasingly present in microbiology laboratories due to its increasing use for bacterial identification. This study describes a method for detection of carbapenemase activity using MALDI-TOF, which is similar to the reference method: the detection of imipenem hydrolysis using UV spectrometry. AbstractWe have evaluated a matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) method for the identification of carbapenemases and for distinguishing metallo-b-lactamases (MBLs). A total of 49 noncarbapenemase-producing and 14 carbapenemase-producing Enterobacteriaceae and Pseudomonas aeruginosa clinical strains, previously characterized by PCR, were included in the study. With MALDI-TOF MS, the presence of carbapenemases was confirmed by the detection of ertapenem hydrolysis (lost of molecular peaks: 476Á5 Da, 498Á5 Da, 520Á5 Da and presence of degradation products) in the mixture of the bacteria with the antibiotic, and classification was achieved by selective inhibition of carbapenemase activity (the ertapenem molecular peak was maintained) with ethylenediaminetetraacetic acid (EDTA). We obtained a good concordance among the results of PCR and MALDI-TOF MS. This method appears to be simple, fast and reliable for distinguishing in few hours different classes of carbapenemases, which can be very useful for epidemiological studies or to establish a specific antimicrobial therapy.

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Objectives: Inappropriate antimicrobial use favours the spread of resistance, and multidrug-resistant microorganisms (MDR) are currently of major concern. Antimicrobial stewardship programmes (ASPs) are essential for improving antibiotic use in hospitals. However, their impact on entire healthcare systems has not been thoroughly assessed. Our objective was to provide the results of an institutionally supported ASP involving 31 public hospitals in Andalusia, Spain. Methods: We designed an ecologic time-series study from 1 January 2014 to 31 December 2017. Quarterly, data on indicators were collected prospectively, and feedback reports were provided. PIRASOA is an ongoing clinically based quality-improvement programme whose key intervention is the educational interview, regular peer-to-peer interventions between advisors and prescribers to reinforce the appropriate use of antibiotics. Seventy-two indicators were monitored to measure prescribing quality (inappropriate treatments), antimicrobial consumption (defined daily doses per 1000 occupied bed-days), incidence density of MDR per 1000 occupied bed-days and crude mortality rate associated with bloodstream infections. We used Joinpoint regression software to analyse the trends. Results: The quality of antimicrobial prescribing improved markedly, and the inappropriate treatment rate was significantly lower, with quarterly percentage change (QPC) ¼ À3.0%, p < 0.001. Total antimicrobial consumption decreased (QPC ¼ À0.9%, p < 0.001), specifically carbapenems, amoxicillin/clavulanic acid, quinolones and antifungal agents, whereas antipseudomonal cephalosporin use increased.

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