Antimicrobial Susceptibility Testing for Colistin: Extended Application of Novel Quantitative and Morphologic Assay...

Area of Science:

• Microbiology
• Microbial Pathogenesis
• Antimicrobial Resistance

Background:

• Colistin (Polymyxin E) is crucial for treating multidrug-resistant (MDR) Gram-negative infections.
• Conventional Colistin antibiotic susceptibility testing (AST) methods are time-consuming and impractical for routine use.

Purpose of the Study:

• To introduce and validate a rapid SEM-AST technique for Colistin susceptibility testing.
• To enable quick detection of Colistin resistance by observing bacterial morphological changes.

Main Methods:

• Utilized scanning electron microscopy (SEM) to analyze morphological changes in Gram-negative bacteria exposed to Colistin.
• Employed Phosphotungstic Acid (PTA) staining and SEM imaging at various magnifications.
• Quantified bacterial viability and morphological alterations over a 120-minute incubation period.

Main Results:

• Susceptible strains showed a significant decrease in viable organisms from 30 minutes post-exposure.
• Distinct morphological changes (inflation, fusion, lysis) were observed as early as 30 minutes in susceptible strains.
• SEM-AST results correlated with gold standard broth microdilution methods.

Conclusions:

• The SEM-AST assay provides a rapid and reliable method for determining Colistin susceptibility.
• This technique offers a significant advancement for the clinical management of MDR Gram-negative infections.
• Demonstrated proof of concept for SEM-AST application across clinically relevant bacterial species.