Potential impact of biofilms on bacterial resistance. Potential impact of biofilms on bacterial resistance. There is an abrupt drop in concentration if the antimicrobial fails to penetrate the biofilm (solid line). The biofilm protects the bacteria leading to treatment failure, but there is relatively little selection for resistance. However, if the antimicrobial can partially penetrate the biofilm there may be a gradual drop in concentration (dotted line). The intermediate concentrations will kill more susceptible bacteria but allow more resistant mutants to survive and proliferate. This will result in treatment failure and recrudescence of the infection with a more resistant isolate. These data are taken from theoretical and in vitro studies Tim Nuttall In Practice 2016;38:17-21 Copyright © British Veterinary Association. All rights reserved.