(596ay) A Multiplexed Microfluidic Platform for Antibiotic Susceptibility Screening

In this work, we report a multiplexed microfluidic platform for rapid characterization of antibiotic susceptibilities in microbial pathogens for healthcare applications.  Antibiotic abuse over the last few decades has resulted in an escalating emergence of multidrug resistant pathogens that respond poorly to conventional antibiotic therapy [1]. As resistance to single antibiotics evolves very rapidly, drug resistant pathogens are usually treated with combinations of antibiotics. However, existing techniques to decide the right therapeutic combinations are time-consuming, laborious, and require substantial volumes of patient body fluids like sputum and blood. Consequently, there is a pressing need for expedited diagnostic platforms. To address this, we designed and fabricated a 4x6-array microfluidic chip capable of confining cells and reagents in nanoliter volume compartments.  Leak-free isolation of contiguous compartments is achieved with elastomeric valves that are closed at rest [2].  Actuation of the normally closed valves with negative pressure enables controlled exposure of cells to antibiotics that are loaded in adjacent compartments.  The miniaturized device design is highly convenient for biological assays as it facilitates portability, uses microliter volumes of samples and reagents for analysis, and is readily amenable to automation. Most importantly, the microfluidic diagnostic platform considerably accelerates assay time due to increased detection sensitivity since it enables analysis at single cell resolution.

We employed the microfluidic platform to investigate susceptibilities of E. coli and P. aeruginosa cells to several commonly used antibiotics. Specifically, we assessed the effects of ampicillin, tetracycline, chloramphenicol, cephalexin, ciprofloxacin, and combinations thereof on E. coli MG1655 and P. aeruginosa PAO1 cells. Furthermore, we quantified synergistic effects of several antibiotic combinations.  As an example, although ampicillin at 10µg/mL and tetracycline at 1 µg/mL are ineffective individually, they exhibit significant bactericidal activity against E. coli when administered in combination.  Finally, we extended the platform to characterize antibiotic resistance in a mixed microbial community of E. coli and P. aeruginosa cells.  Overall, these results emphasize the utility of the microfluidic platform for rapidly characterizing antibiotic susceptibilities over a wide range of antibiotic concentrations.  The platform improves significantly on existing diagnostic methods (disc diffusion and broth dilution assays) in terms of several key advantages including turn-around time, analysis cost, ease-of-use, detection sensitivity, and sample volumes required for diagnosis [3].  

References:

[1] K. Churski et al., Lab Chip, 2012,12.

[2] R Mohan et al., Sensors and Actuators B, 2011, 1, 1216-1223.

[3] JP Torella et al., PLoS Comput Biol, 2010, 6.