Optimization of on-chip bacterial culture conditions using the Box-Behnken design response surface methodology for faster drug susceptibility screening.

Optimized culture conditions are essential for the investigation of biological processes. In this work, on-chip optimization of bacterial culture conditions by combining microfluidics with the Box-Behnken design response surface methodology is presented. With this methodology, the effects of several cultivation variables and their interactions were investigated enabling very fast drug susceptibility screening. The proposed measurement protocol for the determination of minimum inhibitory concentration (MIC) consist of three steps: i) single factor experiments to determine the effect of pH, nutrient concentration, and temperature on the bacterial culture; ii) analyses of the relationship between variables and the effect of the individual variables by means of the Box-Behnken design and response surface methodology (BBD-RSM) optimization; and iii) bacterial susceptibility screening of drugs and drug combinations. BBD-RSM is efficient to determine the optimal growth conditions of bacteria species with a strongly reduced amount of required experiments. On top of that, these experiments can in principle all be performed at the same time, yielding significant time-savings. The found optimized culture conditions of E. coli were applied to determine the MIC values of the drugs penicillin-streptomycin and baicalein, and combinations of those. MIC values were obtained within 8-14 h, including the 6-8 h required to determine the optimal growth parameters. The microfluidic BBD-RSM method results in a significant time reduction compared to the standard 2-4 days required to determine MIC values and is, therefore, a potential alternative in the management of bacterial infections.