Direct antimicrobial susceptibility testing of bloodstream infection on SlipChip

This paper describes an integrated microfluidic SlipChip device for rapid antimicrobial susceptibility testing (AST) of bloodstream pathogens in positive blood cultures. Unlike conventional AST methods, which rely on an overnight subculture of positive blood cultures to obtain isolated colonies, this device enables direct extraction and enrichment of the bacteria from positive blood cultures by dielectrophoresis. SlipChip technology enables parallel inoculation of the extracted bacteria into nanoliter-scale broth droplets to perform multiplexed ASTs simultaneously. The nanoliter confinement in the droplets increases the effective inoculation amount of the bacteria, shortens the diffusion distance of nutrient elements and gases, and allows faster growth and proliferation rates. Entropy-based image analysis used for the characterization of bacterial susceptibility patterns eliminates the requirement for single-cell morphological analysis and fluorescence labeling. As a proof-of-concept, the susceptibility patterns of Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 6538p, and a positive blood culture containing Escherichia coli against several broad-spectrum antibiotics were determined by the SlipChip device. The on-chip AST results were well matched with those respectively reported by the broth microdilution method and a BD Phoenix Automated Microbiology System. Reliable AST results can be reported to clinicians within 3-8 h using this simple device after positive blood culture, allowing earlier proper administration of antimicrobial therapy.