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Published on: April 18, 2019
Evaluation of susceptibility testing methods for polymyxin
Bijayini Behera1, Purva Mathur, Anupam Das
1Department of Laboratory Medicine, Jai Prakash Narain Apex (JPNA) Trauma Centre, All India Institute of Medical Sciences (AIIMS), New Delhi, 110029 India.
Background:
The widespread resistance in Gram-negative bacteria has necessitated evaluation of the use of older antimicrobials such as polymyxins. In the present study we evaluated the different susceptibility testing methods for polymyxins B and E against Gram-negative bacteria using the new Clinical and Laboratory Standards Institute (CLSI) guidelines.
Methods:
The susceptibility of 281 multidrug-resistant (MDR) Gram-negative bacteria (GNB) to polymyxin B was evaluated, comparing broth microdilution (BMD; reference method), agar dilution, E-test, and disk diffusion. Disk diffusion testing of polymyxin B was also performed against 723 MDR GNB.
Results:
Twenty-four of 281 (8.5%) isolates were found to be resistant to polymyxin B by the reference BMD method. The rates of very major errors for agar dilution and E-test (for polymyxin B) were 0.7% and 1%, respectively, and those for disk diffusion (for polymyxin B and polymyxin E) were 1% and 0.7%, respectively. For the 257 isolates found sensitive by reference BMD, the rates of major errors by agar dilution and E-test (for polymyxin B) were 2.4% and 0%, respectively, and those for disk diffusion (polymyxin B and polymyxin E) were 0% and 0.7%, respectively. Twenty-six (3.6%) of the 723 Gram-negative isolates were resistant to polymyxin B by disk diffusion.
Conclusion:
The E-test and agar dilution methods showed good concordance with BMD. The disk diffusion method can be useful for initial screening in diagnostic laboratories.
Insights
Evaluating polymyxin susceptibility testing methods for Gram-negative bacteria is crucial due to widespread resistance. The E-test and agar dilution methods show good concordance with the reference method, while disk diffusion is useful for initial screening.
Area of Science:
- Microbiology
- Clinical Laboratory Science
- Antimicrobial Resistance
Background:
- Rising antimicrobial resistance in Gram-negative bacteria necessitates evaluating older drugs like polymyxins.
- The study addresses the need for reliable susceptibility testing methods for polymyxins B and E.
- New Clinical and Laboratory Standards Institute (CLSI) guidelines were used for evaluation.
Purpose of the Study:
- To evaluate various susceptibility testing methods for polymyxins B and E against Gram-negative bacteria.
- To compare the accuracy and concordance of broth microdilution, agar dilution, E-test, and disk diffusion methods.
- To assess the utility of different methods in the context of increasing antimicrobial resistance.
Main Methods:
- Susceptibility testing of 281 multidrug-resistant Gram-negative bacteria (GNB) to polymyxin B using broth microdilution (BMD; reference), agar dilution, E-test, and disk diffusion.
- Disk diffusion testing of polymyxin B was also performed on an additional 723 MDR GNB isolates.
- Error rates (very major and major) were calculated for each method compared to BMD.
Main Results:
- Twenty-four of 281 (8.5%) isolates were resistant to polymyxin B by the reference BMD method.
- Agar dilution and E-test demonstrated low rates of very major errors (0.7% and 1%) for polymyxin B.
- Disk diffusion showed low error rates for both polymyxin B (1%) and polymyxin E (0.7%) for very major errors and minimal major errors.
- Twenty-six (3.6%) of 723 GNB were resistant to polymyxin B by disk diffusion.
Conclusions:
- E-test and agar dilution methods exhibit good concordance with the reference broth microdilution method.
- Disk diffusion can serve as a valuable initial screening tool in diagnostic laboratories for polymyxin susceptibility.
- These findings support the use of validated methods for accurate polymyxin susceptibility testing in clinical settings.
