The paper describes a droplet-based microfluidic method for phenotypic-based antimicrobial susceptibility testing (AST). In particular, this micro-droplet-based phenotypic assay evaluates susceptibility of different bacterial strains towards antibiotics by tracking effects on individual bacterial cells, including changes in bacterial cell number and morphology. The platform was validated by applying the method to test the responses of E. coli ATCC 25922 and 6937 (a clinical isolate), in spiked urine samples at a concentration of 5 × 104 cfu mL−1, to the antibiotics ceftazidime and levofloxacin. Both E. coli strains showed dose-dependent inhibition of bacterial replication and morphological alteration. These correlated well with minimal inhibitory concentrations determined by the reference broth microdilution method. Discrete bacterial divisions and morphological changes were observed within 20 min of on-chip incubation, demonstrating performance of rapid AST directly on urine samples. As proof-of-concept, specific bead-based biosensors were tested for capture and detection of E. coli for on-bead proliferation. The method has the attractive feature of allowing the detection of at least one bacterium per bead in less than 30 min. It can potentially be used to isolate a specific bacterial strain directly from patient urine samples for AST monitoring. [Figure not available: see fulltext.].
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Acknowledgements The authors would like to acknowledge Abhinav Gupta, Sneha Varghese and Sai Mynampati at Northeastern University for their assistance in fabrication of microfluidic devices. The authors would like to thank Zhi Shen Lin (Northeastern University) for his assistance in bacterial cell culture. The authors would also like to acknowledge the CIMIT grant awarded to Dr. Konry (CIMIT/POCT/NIH/NIBIB/ 16111315).
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- Antibiotic susceptibility
- Bioassay development
- Droplet microfluidics
- E. coli
- Fluorescence microscopy
- Urinary tract infections