An Individual-based Model for Simulating Antibiotic Resistance Spread in Bacterial Flocs in Wastewater Treatment Plants

Wastewater treatment plants (WWTPs) receive wastewater that carries a variety of pollutants, including antibiotics and antibiotic-resistant bacteria. The potential for horizontal gene transfer of resistance through conjugation – direct cell-to-cell transfer of genes carried on a plasmid – is high in WWTPs because of high cell density and residence time in bacterial flocs. To better understand how resistance spreads by growth and conjugation in such flocs, we propose an individual-based model with a solver algorithm for dynamic simulation. Our model includes only the most relevant bacteria properties and functions such as movement, growth, division, gene transfer, and death. Simulation of our model suggests that resistance can increase by conjugation at the early growth stages of a floc and that the overall rate of gene transfer depends on floc size. Results indicate that our simple model can be a useful tool for examining how gene exchange and heterogeneity contribute to the spread of antibiotic resistance in bacterial flocs