Antimicrobial Susceptibility Testing for Polymyxins: Challenges, Issues, and Recommendations

Area of Science:

• Clinical Microbiology
• Infectious Diseases
• Pharmacology

Background:

• Polymyxins (polymyxin B and colistin) are vital for treating multidrug-resistant (MDR) Gram-negative bacterial infections.
• Accurate susceptibility testing is essential due to increasing polymyxin use.
• Several factors complicate polymyxin susceptibility testing.

Purpose of the Study:

• To review challenges in polymyxin susceptibility testing.
• To discuss emerging polymyxin resistance mechanisms.
• To highlight the need for reliable testing methods.

Main Methods:

• Literature review of polymyxin susceptibility testing methods.
• Discussion of factors affecting test accuracy.
• Overview of polymyxin resistance mechanisms.

Main Results:

• Difficulties include drug composition, diffusion, adsorption, lack of reliable tests and breakpoints, polysorbate 80 synergy, and heteroresistance.
• Emerging resistance mechanisms involve chromosomally and plasmid-mediated mcr genes.
• Current methods face significant limitations.

Conclusions:

• Addressing polymyxin testing challenges is critical for effective MDR Gram-negative infection treatment.
• Further research is needed to improve polymyxin susceptibility testing.
• Understanding resistance mechanisms is key to guiding therapy.