Rapid antibiotic susceptibility testing by tracking single cell growth in a microfluidic agarose channel system

Sepsis is one of the major causes of death in the US, necessitating rapid treatment with proper antibiotics. Conventional systems for antibiotic susceptibility testing (AST) take far too long (16-24 h) for the timely treatment of sepsis. This is because they rely on measuring optical density, which relates to bacterial growth, to determine the minimal inhibitory concentrations (MICs) of relevant antibiotics. Thus, there is a desperate need for more improved and rapid AST (RAST) systems. The RAST system can also reduce the growing number of clinical problems that are associated with antibiotic resistance caused by methicillin-resistant Staphylococcus aureus, vancomycin-resistant Staphylococcus aureus, and vancomycin-resistant enterococci. In this study, we demonstrate a microfluidic agarose channel (MAC) system that reduces the AST assay time for determining MICs by single bacterial time lapse imaging. The MAC system immobilizes bacteria by using agarose in a microfluidic culture chamber so that single cell growth can be tracked by microscopy. Time lapse images of single bacterial cells under different antibiotic culture conditions were analyzed by image processing to determine MICs. Three standard bacteria from the Clinical and Laboratory Standard Institute (CLSI) were tested with several kinds of antibiotics. MIC values that were well matched with those of the CLSI were obtained within only 3-4 h. We expect that the MAC system can offer rapid diagnosis of sepsis and thus, more efficient and proper medication in the clinical setting.