(394k) A Combinatorial Microfluidic Approach for Point-of-Care Applications

We describe a microfluidic platform with optimized normally closed valves for high throughput quantitative analyses of stimulus driven responses in E. coli cells [1]. Specifically, we designed and fabricated a 4x6-array microfluidic chip capable of confining cells and reagents in sub-micron volume compartments. Leak-free isolation of contiguous compartments is achieved with elastomeric valves that are closed at rest [2]. Actuation of valves with negative pressure permits controlled exposure of cells confined in ~2 nL volume compartments to various chemical stimuli loaded in adjacent compartments. The device design is convenient for biological assays due to increased detection sensitivity, thereby enabling analysis at single cell resolution. Additionally, the device facilitates portability and exhibits multiple advantages as a miniaturized biological assay, including low sample and reagent volumes for analysis and integration of assay steps in an on-chip format. The overall goal of this work is to develop a diagnostic platform for screening antibiotic resistant phenotypes in infected clinical samples.

In this work, we employ the microfluidic platform to investigate antibiotic susceptibilities of E. coli cells to several commonly used antibiotics. Furthermore, we explore the synergistic and antagonistic effects of antibiotic combinations on E. coli cell proliferation. Specifically, we investigate the effects of ampicillin, tetracycline, chloramphenicol, cephalexin, ciprofloxacin, and combinations thereof on actively growing E. coli cells. The results were used to determine effective bactericidal and bacteriostatic concentrations for the aforementioned antibiotics (e.g., > 100 μg/mL for ampicillin, > 10 μg/mL for tetracycline). We also observed and characterized synergistic effects of certain antibiotic combinations. For example, although ampicillin at 10 μg/mL and tetracycline at 1 μg/mL are ineffective individually, together they exhibit significant bactericidal activity when used in combination. Finally, we extended the platform to characterize antibiotic resistance in a model pathogen, Pseudomonas aeruginosa.

Overall, these results emphasize the utility of the microfluidic platform for rapidly characterizing antibiotic susceptibilities over a wide range of concentrations. The platform improves on existing diagnostic methods in terms of assay time, ease-of-use, sensitivity, and sample volumes [3]. The described microfluidic platform is expected to expedite elucidation of treatment regimens necessary for combating infections with multi-antibiotic resistant “superbugs” that represent an emerging and acute global health concern. 

References: 

[1] R Mohan et al., MicroTAS, 2011, Seattle, USA. 

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

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