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Polymyxin susceptibility testing, interpretative breakpoints and resistance mechanisms: An update
Yamuna Devi Bakthavatchalam1, Agila Kumari Pragasam1, Indranil Biswas2
1Department of Clinical Microbiology, Christian Medical College, Vellore 632004, Tamil Nadu, India.
Journal of Global Antimicrobial Resistance
|October 1, 2017
Summary
Accurate polymyxin susceptibility testing is crucial for treating multidrug-resistant infections. This review discusses challenges and methods for testing colistin and polymyxin B, including new resistance mechanisms.
Area of Science:
- Clinical microbiology
- Infectious diseases
- Antimicrobial resistance
Background:
- Multidrug-resistant (MDR) nosocomial pathogens pose a significant threat.
- Polymyxins are last-resort antibiotics for MDR Gram-negative bacterial infections.
- Routine polymyxin susceptibility testing is essential due to increased usage.
Purpose of the Study:
- To review current polymyxin susceptibility testing methods.
- To discuss challenges impacting test performance.
- To describe emerging resistance mechanisms.
Main Methods:
- Literature review of available susceptibility testing methods.
- Discussion of factors affecting test accuracy (e.g., drug composition, diffusion, adsorption, synergy).
- Overview of identified chromosomal and plasmid-mediated resistance mechanisms.
Main Results:
- Polymyxin susceptibility testing is challenging due to drug properties and interactions.
- Factors like multicomponent composition, poor agar diffusion, and polysorbate 80 synergy affect results.
- New resistance mechanisms include LPS modification (L-Ara4-N, pEtN) and plasmid-borne mcr genes.
Conclusions:
- Standardized and reliable polymyxin susceptibility testing methods are needed.
- Understanding resistance mechanisms is vital for effective treatment strategies.
- Continued research is necessary to combat emerging MDR pathogens.
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