Abstract
Objective: This study evaluated the capability of a MALDI Biotyper system equipped with the newly introduced MBT STAR-BL module to simultaneously perform species identification and β-lactamase-mediated resistance detection in bacteremia -causing bacteria isolated from cultured isolates and patient-derived blood cultures (BCs).Methods: Two hundred retrospective cultured isolates and 153 prospective BCs containing Gram-negative rods (GNR) were collected and subjected to direct bacterial identification, followed by the measurement of β-lactamase activities against ampicillin, piperacillin, cefotaxime, ceftazidime, and meropenem using the MBT STAR-BL module. The results and turnaround times were compared with those of routine microbiological processing. All strains were also characterized by beta-lactamase PCR and sequencing.Results: Using the saponin-based extraction method, MALDI-TOF MS correctly identified bacteria in 116/134 (86.6%) monomicrobial BCs. The detection sensitivities for β-lactamase activities against ampicillin, piperacillin, third-generation cephalosporin and meropenem were 91.3, 100, 97.9, and 100% for cultured isolates, and 80.4, 100, 68.8, and 40% for monomicrobial BCs (n = 134) respectively. The overall specificities ranged from 91.5 to 100%. Furthermore, the MBT STAR-BL and conventional drug susceptibility test results were concordant in 14/19 (73.7%) polymicrobial cultures. Reducing the logRQ cut-off value from 0.4 to 0.2 increased the direct detection sensitivities for β-lactamase activities against ampicillin, cefotaxime and meropenem in BCs to 85.7, 87.5, and 100% respectively. The MBT STAR-BL test enabled the reporting of β-lactamase-producing GNR at 14.16 and 47.64 h before the interim and final reports of routine BCs processing, respectively, were available.Conclusion: The MALDI Biotyper system equipped with the MBT STAR-BL module enables the simultaneous rapid identification of bacterial species and β-lactamase-mediated resistance from BCs and cultured isolates. Adjustment of the logRQ cut-off value to 0.2 significantly increased the detection sensitivities for clinically important drug-resistant pathogens.
Highlights
Sepsis is a major cause of infectious disease-associated morbidity and mortality (Fleischmann et al, 2016)
The present study aimed to evaluate the ability of the MALDI Biotyper system equipped with the MBT STAR-BL module to identify bacteremia -causing bacteria and predict β-lactam resistance from plated isolates, as well as blood culture (BC) broths
63/66 (95.5%) AMP-resistant E. coli isolates were correctly identified by MBT STAR-BL with 100% specificity (Table 1)
Summary
Sepsis is a major cause of infectious disease-associated morbidity and mortality (Fleischmann et al, 2016). In the absence of automated analysis software, previous studies have used either manual calculations (Sparbier et al, 2012; Ghebremedhin et al, 2016) or self-developed algorithms with ambiguous cut-off values (Jung et al, 2014) to analyze the peak patterns. Bruker Daltonik launched a software module, the MALDI BiotyperTM Selective Testing for Beta-Lactamase Activity (MBT STAR-BL), for the automatic analysis of drug hydrolysis mass spectra. This module facilitates the simultaneous bacterial identification and detection of β-lactamase-mediated resistance toward ampicillin (AMP), piperacillin (PIP), cefotaxime (CTX), ceftazidime (CAZ), meropenem (MEM), and ertapenem (ETP)
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