Sedimentation field-flow fractionation for rapid phenotypic antimicrobial susceptibility testing: a pilot study

Background: The increase in antibiotic resistance is a major public health issue. The development of rapid antimicrobial susceptibility testing (AST) methods is becoming a priority to ensure early and appropriate antibiotic therapy.

Objectives: To evaluate sedimentation field-flow fractionation (SdFFF) as a method for performing AST in less than 3 h.

Methods: SdFFF is based on the detection of early biophysical changes in bacteria, using a chromatographic-type technology. One hundred clinical Escherichia coli strains were studied. A calibrated bacterial suspension was incubated for 2 h at 37°C in the absence (untreated) or presence (treated) of five antibiotics used at EUCAST breakpoint concentrations. Bacterial suspensions were then injected into the SdFFF machine. For each E. coli isolate, retention times and elution profiles of antibiotic-treated bacteria were compared with retention times and elution profiles of untreated bacteria. Algorithms comparing retention times and elution profiles were used to determine if the strain was susceptible or resistant. Performance evaluation was done according to CLSI and the ISO standard 20776-2:2021 with broth microdilution used as the reference method.

Results: AST results from SdFFF were obtained in less than 3 h. SdFFF showed high categorical agreement (99.8%), sensitivity (99.5%) and specificity (100.0%) with broth microdilution. Results for each antimicrobial were also in agreement with the ISO 20776-2 recommendations, with sensitivity and specificity of ≥95.0%.

Conclusions: This study showed that SdFFF can be used as a rapid, accurate and reliable phenotypic AST method with a turnaround time of less than 3 h.