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Evaluation of three different methods for susceptibility testing of gentamicin in carbapenem resistant
Yeliz Tanriverdi Cayci1, Kubra Hacieminoglu Ulker1, Asuman Birinci1
1Department of Medical Microbiology, Faculty of Medicine, Ondokuz Mayıs University, Samsun, Turkey.
Abstract:
Carbapenem-resistant Enterobacterales (CRE) have become a growing problem worldwide in recent years. Options for the treatment of CRE are limited and one of these options is gentamicin. For this reason, gentamicin susceptibility should be properly determined. In a recently reported study, it is recommended to review the results of automated systems for assessing gentamicin susceptibility in carbapenem-resistant isolates. In this study, we aimed to determine gentamicin susceptibility using three different methods and compare the methods. The study included 107 CRE isolates from different samples. Gentamicin susceptibility was determined using Vitek 2 Compact (bioMérieux, France), Microscan Walkaway Plus (Beckman Coulter, USA) automatic systems, and disk diffusion (DD) method. The broth microdilution method (BMD) was used as reference method. Minor, major, and very major errors and categorical agreement rates were determined for each method. Aminoglycoside-modifying enzymes (aac(6')Ib and aph(2″)Ia) were assayed in discrepant isolates. According to BMD results, 90.7%, 1,8 %, and 7.5 % of the isolates were determined as susceptible, intermediate, and resistant to gentamicin, respectively. Compared to the results of the BMD for detecting gentamicin susceptibility, disk diffusion method showed the highest categorical agreement (98.1%), and Vitek 2 Compact showed the lowest categorical agreement (90.6%). The very major error rates were determined 7.5%, 0.9%, and 0.9% for Vitek 2 Compact, Microscan Walkaway Plus, and DD method, respectively. In addition, aac(6')Ib and aph(2″)Ia genes were detected in 8 discrepant isolates. For gentamicin susceptibility, the DD showed the most compatible results. The DD can be used as a reliable method for determining gentamicin susceptibility. Compatibility of automated systems with BMD was acceptable, although lower than DD. The discrepancies detected in the Vitek 2 Compact results could be due to the presence of aac(6')Ib and/or aph(2″)Ia aminoglycoside-modifying enzymes.
Insights
Determining gentamicin susceptibility in carbapenem-resistant Enterobacterales (CRE) is crucial. The disk diffusion method demonstrated the highest accuracy compared to automated systems and broth microdilution, making it a reliable option.
Area of Science:
- Clinical Microbiology
- Antimicrobial Resistance
- Infectious Diseases
Background:
- Carbapenem-resistant Enterobacterales (CRE) pose a significant global health threat due to limited treatment options.
- Gentamicin remains a key therapeutic agent for CRE infections, necessitating accurate susceptibility testing.
- Previous studies suggest a need to evaluate automated systems for gentamicin susceptibility testing in CRE.
Purpose of the Study:
- To compare the accuracy of three methods for determining gentamicin susceptibility in CRE isolates.
- To assess the performance of automated systems (Vitek 2 Compact, Microscan Walkaway Plus) against the disk diffusion (DD) method and broth microdilution (BMD) as a reference.
Main Methods:
- 107 CRE isolates were tested for gentamicin susceptibility using Vitek 2 Compact, Microscan Walkaway Plus, and DD methods.
- Broth microdilution (BMD) served as the gold standard for comparison.
- Categorical agreement, minor, major, and very major errors were analyzed. Aminoglycoside-modifying enzyme genes were investigated in discrepant results.
Main Results:
- The disk diffusion (DD) method exhibited the highest categorical agreement (98.1%) with BMD.
- Vitek 2 Compact showed the lowest agreement (90.6%), with a high very major error rate (7.5%).
- Aminoglycoside-modifying enzyme genes (aac(6')Ib, aph(2″)Ia) were identified in 8 discrepant isolates.
Conclusions:
- The disk diffusion (DD) method is a reliable and accurate approach for determining gentamicin susceptibility in CRE.
- Automated systems demonstrated acceptable, though lower, agreement with BMD compared to DD.
- Discrepancies with automated systems may be linked to the presence of specific aminoglycoside-modifying enzymes.
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