Metallo-βeta-Lactamase Detection Comparative Evaluation of Double-Disk Synergy versus Combined Disk Tests

  • Naima Mehdi Consultant Pathologist, Punjab Institute of Cardiology Lahore Pakistan
  • Nadia Aslam Associate Professor of Pathology, Rai Medical College Sargodha Pakistan
  • Muhammad Saeed Medical Lab Technologist District Head Quarter Hospital Mandi Bahauddin Pakistan
  • Abdul Wadood Khalid Senior Consultant Pathologist, Punjab Institute of Cardiology Lahore Pakistan
  • Saba Riaz Assistant Professor Microbiology Punjab University Lahore Pakistan
  • Mateen Izhar Professor of Pathology, Sheikh Zaid Medical Complex Lahore Pakistan
Keywords: Double disk synergy technique, Metallo-β-lactamases


Objective: To establish (i) if carbapenemases are a major cause of carbapenem resistance in Enterobacteriaceae and belong to metallo- β-lactamases (ii) Which one is the best phenotypic method for the detection of metallo- β-lactamases.
Patients and Methods: This cross-sectional study was conducted at pathology department, Punjab Institute of Cardiology Lahore. Samples were randomly enrolled from daily lab work and analysed. During the period of September 2016 to January 2017, a total of 2970 clinical samples were enrolled and processed for bacterial culture. Every isolate of Enterobacteriaceae was processed for detection of carbapenem resistance and for the detection of carbapenemases producers by modified Hodge test. Metallo- β-lactamases detection (MBL) was done by three different phenotypic techniques, (i) Combined disk technique (0.1 M EDTA), (ii) (0.5 M EDTA). (iii) Double disk synergy technique (DSST).
Results: Out of total n=2970 samples, 38.7% (n=1150) were culture positive of which 40.5% (n=550) were Enterobacteriaceae. Among these, 9.0 % (n=50) were carbapenem-resistant; 98% (49/50) were carbapenemase producers (modified Hodge test -Positive). According to (i) Combined disk technique (0.1 M EDTA), 98% (48/49) were metallo- β-lactamases positive (ii) Combined disk technique (0.5 M EDTA), 86% (42/49) were metallo- β-lactamases, 2% (1/49) were non-determinable (iii) Double disk synergy technique (DDST) showed 100% (49/49) isolates were metallo- β-lactamases positive. Chloramphenicol and Tigecycline were found sensitive in 28% and 16% respectively; all other antimicrobials were highly resistant against carbapenem-resistant isolates.
Conclusion: Carbapenemases are a major cause of carbapenem resistance in Enterobacteriaceae. Double-disk synergy technique is good for the detection of MBL as compared to other phenotypic methods. Each carbapenemresistant isolate of Enterobacteriaceae should be process for the detection of Carbapenemase especially MBL.

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