High-throughput, multiplex microfluidic test strip for the determination of antibiotic susceptibility in uropathogenic E. coli with smartphone detection

Antibiotic resistance in urinary tract infections is a major global challenge and improved cost-effective and high throughput antibiotic susceptibility tests (AST) are urgently needed to inform correct antibiotic selection. We evaluated a high throughput microfluidic test strip for AST and minimum inhibitory concentration (MIC) determination in 20 urinary pathogenic E. coli (UPEC) isolates using six commonly prescribed or therapeutically beneficial antibiotics. The microfluidic MIC performs broth microdilution in 1 microliter volume capillaries, 100 X smaller than standard broth microdilution. Each test strip contains 10 parallel capillaries which are dipped into a single well of a 96 well plate, significantly increasing throughput over a microtitre plate. When tested with clinical UPEC isolates at standardised inoculum density, these devices gave 100% essential agreement (+/- 1 doubling dilution of antibiotic) to the gold standard microplate broth microdilution method described by CLSI. Although for some antibiotic/isolate combinations an earlier endpoint readout reduced accuracy, MIC test strips read at a 6h endpoint still gave 69 – 100 % essential agreement depending on the antibiotic. Growth could be detected significantly earlier than 6h, but with a trade-off between speed vs accuracy. These high-throughput, multiplexed test strips could be used to increase throughput and give faster results than microplates while retaining the core broth microdilution methodology of gold standard techniques for AST and MIC determination. ### Competing Interest Statement ADE is one of the inventors of patent application protecting aspects of the novel microfluidic devices tested in this study and is a director and shareholder in Capillary Film Technology Ltd, a company holding a commercial license to this patent application: WO2016012778. Capillary assay device with internal hydrophilic coating. AD Edwards, NM Reis.