An update on polymyxin susceptibility testing methods for Acinetobacter baumannii.

Area of Science:

• Clinical Microbiology
• Antimicrobial Resistance
• Infectious Diseases

Background:

• Carbapenem-resistant Acinetobacter baumannii (CRAB) is a significant cause of severe hospital-acquired infections with high mortality.
• Polymyxins are the last-resort treatment for CRAB infections, making susceptibility testing (ST) critical.
• Existing in vitro ST methods for polymyxins against CRAB exhibit notable discrepancies and limitations.

Purpose of the Study:

• To review current polymyxin susceptibility testing methods for CRAB.
• To discuss challenges in obtaining and interpreting valid susceptibility results in clinical laboratories.
• To highlight the need for improved standardization and harmonization of polymyxin ST methods.

Main Methods:

• Literature review of studies on polymyxin ST methods for Acinetobacter spp. published until May 2019.
• Evaluation of various in vitro susceptibility testing methodologies.
• Consideration of recommendations from the CLSI-EUCAST Working Group.

Main Results:

• No single commercial ST method currently provides fully accurate results for polymyxin susceptibility in CRAB.
• Significant discrepancies exist between different in vitro ST methods.
• Broth microdilution (BMD) without additives is recommended as the reference method by CLSI-EUCAST.

Conclusions:

• Accurate polymyxin susceptibility testing for CRAB is challenging due to method limitations.
• Further optimization, standardization, and international harmonization of ST methods are crucial.
• Improved methods are needed to facilitate the accurate detection of polymyxin-resistant Acinetobacter baumannii.