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Front. Microbiol. | doi: 10.3389/fmicb.2018.00334

Comprehensive Evaluation of the MBT STAR-BL module for Simultaneous Bacterial Identification and β-lactamase-mediated Resistance Detection in Gram-negative Rods from Cultured Isolates and Positive Blood Cultures

 Wing Tung LEE1, Johnson Keung Sang Lam2, Ricky Ka Wai Lam2, Wan Han Ng2, Ella Nga Lam Lee1, Vicky Tsui Yin Lee3, Po Po Sze1,  Rahim Rajwani1, Kitty Sau Chun Fung4, Wing Kin To5, Rodney Allen Lee3, Dominic Nga Chong Tsang2 and  Kit Hang Gilman Siu1*
  • 1Hong Kong Polytechnic University, Hong Kong
  • 2Queen Elizabeth Hospital (QEH), Hong Kong
  • 3Pamela Youde Nethersole Eastern Hospital, Hong Kong
  • 4United Christian Hospital, Hong Kong
  • 5Princess Margaret Hospital, Hong Kong

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.

Keywords: MBT STAR-BL, MALDI-TOF MS, Drug Resistance, Bacterial, drug hydrolysis test, beta-Lactamases, Blood culture

Received: 31 Aug 2017; Accepted: 12 Feb 2018.

Edited by:

Karsten Becker, Universität Münster, Germany

Reviewed by:

Jaroslav Hrabak, Faculty of Medicine in Pilsen, Charles University, Czechia
Irene Burckhardt, Department for Infectious Diseases, University of Heidelberg, Germany  

Copyright: © 2018 LEE, Lam, Lam, Ng, Lee, Lee, Sze, Rajwani, Fung, To, Lee, Tsang and Siu. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Kit Hang Gilman Siu, Hong Kong Polytechnic University, Kowloon, Hong Kong,