A Novel Binary Biofilm Coinfection Model for the Simultaneous Growth of Gram-Positive and Gram-Negative Bacterial Species

Objectives: The aim of this study was to determine if it is possible to establish and maintain a binary biofilm consisting of Gram-positive (Bacillus subtilis) and Gram-negative (Escherichia coli) bacteria, which could be used as a multi-species model for antibiotic action studies. Materials and Methods: A medium controlled, continuous culture biofilm model was developed based upon the previously developed Sorbarod™ model. This new model was designed to enable the growth of B. subtilis and E. coli at the same time without either out-competing the other. Results: A pseudo-steady-state binary biofilm was established, which could be maintained for a total of 53 hours. This biofilm was tested to confirm the ability of the biofilm model to support the growth of a Gram-positive (Bacillus subtilis) and a Gram-negative (Escherichia coli) bacterial species under the same conditions of media throughput, aeration and temperature. Conclusions: This paper gives evidence of the ability to develop and control binary biofilm models to maintain the growth of two Gram-dissimilar species of bacteria. We believe this is a novel concept and will aid the future in vitro assessment of antibiotic activity in coinfection models.