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Published on: September 9, 2015
Comparison of Broth Disk Elution and Broth Microdilution Methods for Colistin Susceptibility Testing in
Priyanka M Chandankhede1, Rajesh P Karyakarte1, Ashish Sadafale1
1Microbiology, B. J. Government Medical College & Sassoon General Hospitals, Pune, IND.
Background:
The increasing prevalence of carbapenem-resistant Enterobacteriaceae (CRE) and Pseudomonas aeruginosa (CRPA) poses a significant challenge to clinical management, particularly in resource-limited settings. Colistin remains one of the last-resort antibiotics for treating these infections; however, its accurate susceptibility testing remains technically challenging. The Broth Microdilution (BMD) method, though recommended as the reference standard, is labor-intensive and not feasible for routine use in most laboratories. This study aims to evaluate the Colistin Broth Disk Elution (CBDE) method as a practical alternative to BMD.
Materials And Methods:
This cross-sectional study was conducted over 18 months (December 2022 to June 2024) at a tertiary care microbiology laboratory in India. A total of 120 non-duplicate CRE and CRPA isolates from clinical specimens were randomly selected and tested for colistin susceptibility using both BMD and CBDE methods. MIC interpretations were based on CLSI 2024 guidelines. Categorical agreement (CA), essential agreement (EA), and error rates were analyzed as per CLSI 2015 recommendations.
Results:
Out of 120 carbapenem-resistant isolates included in the study, 92 (76.67%) were CRE and 28 (23.33%) were CRPA. Colistin resistance was detected in six (5%) and four (3.33%) isolates by BMD and CBDE, respectively. CBDE showed a CA of 98.3% (95% confidence Interval: 94.1%-99.8%) and EA of 100% when compared to BMD, with only two minor errors (1.6%) and no major or very major errors.
Conclusion:
CBDE demonstrated high categorical agreement with BMD and minimal error and offers a simple, cost-effective alternative for routine colistin susceptibility testing, especially in low-resource settings where BMD is not feasible.
Insights
The Colistin Broth Disk Elution (CBDE) method is a reliable and cost-effective alternative for colistin susceptibility testing. It shows high agreement with the reference method, making it suitable for resource-limited settings.
Area of Science:
- Clinical Microbiology
- Antimicrobial Resistance
- Infectious Diseases
Background:
- Rising rates of carbapenem-resistant Enterobacteriaceae (CRE) and Pseudomonas aeruginosa (CRPA) present a global health challenge.
- Colistin is a critical antibiotic for treating infections caused by these multidrug-resistant organisms.
- Accurate colistin susceptibility testing is vital but challenging, with the standard Broth Microdilution (BMD) method being labor-intensive.
Purpose of the Study:
- To evaluate the Colistin Broth Disk Elution (CBDE) method as a practical alternative to BMD for colistin susceptibility testing.
- To assess the performance of CBDE against the reference BMD method.
- To determine the suitability of CBDE for routine use, particularly in resource-limited laboratories.
Main Methods:
- A cross-sectional study involving 120 non-duplicate CRE and CRPA isolates was conducted over 18 months.
- Colistin susceptibility was tested using both BMD and CBDE methods.
- Categorical agreement (CA), essential agreement (EA), and error rates were analyzed according to CLSI guidelines.
Main Results:
- The study included 92 CRE and 28 CRPA isolates.
- CBDE demonstrated a high categorical agreement (98.3%) and 100% essential agreement with BMD.
- Only two minor errors (1.6%) were observed with CBDE, with no major or very major errors.
Conclusions:
- The CBDE method is a simple, cost-effective, and accurate alternative for colistin susceptibility testing.
- CBDE exhibits high agreement with the reference BMD method, making it suitable for routine use.
- This method is particularly valuable for resource-limited settings where BMD is not feasible.
