A microfluidic approach to study the effect of bacterial interactions on antimicrobial susceptibility in polymicrobial cultures

Polymicrobial infections are caused by more than one pathogen. They require antimicrobial dosing regimens that are different from those prescribed for monomicrobial infections because these interactions are predicted to influence the antimicrobial susceptibility of the individual pathogens. Here we report on a microfluidic approach to study the effect of bacterial interactions in polymicrobial cultures on the antimicrobial susceptibility. The use of microfluidics enables real-time quantification of bacterial growth dynamics in the presence and absence of antimicrobials, which is challenging to achieve using current methods. We studied microbial interactions between Pseudomonas aeruginosa, and Escherichia coli and Klebsiella pneumoniae. A key observation was that in co-cultures with relatively high initial cell numbers of P. aeruginosa, the co-cultured partner bacteria exhibited initial growth followed by lyses or growth stasis. In addition, we observed a significantly higher antimicrobial tolerance of P. aeruginosa in polymicrobial cultures, as evident by up to 8-fold increases in the minimum inhibitory concentration of the antimicrobials, compared to those observed in monomicrobial cultures. This work demonstrates the potential of microfluidics to study bacterial interactions and their effect on antimicrobial susceptibility, which in turn will aid in determining appropriate antimicrobial treatment for polymicrobial infections.