9/18/2016 Factors that Govern Antimicrobial 5 Protective Mechanisms Resistance of a Biofilm Mechanisms of Biofilm Tolerance Thickness,age,density simple inverse relationship between biomass and susceptibility cannot be made Presence of abiotic particles reduce diffusive transport increase sorptive capacity Concentration of antimicrobial agent higher doses than for planktonic Species composition co-culturing species improve resistance Genetic makeup of the microbe-role remains unclear Defense mechanisms No/slow growth zones VBNC cells Persister cells:subpopulation of microbes Multicellular Characteristics of Biofilms with genetic characteristics that allow their survival when exposed to an antibiotic without Contribute to Bacterial Survivability within a Biofilm undergoing genetic change:type of dormant cell involves a metabolic shutdown not a genetic mutation 119/18/2016 11 Factors that Govern Antimicrobial Resistance of a Biofilm • Thickness, age, density • si l i s l ti shi b t bi ss d simple inverse relationship between biomass and susceptibility cannot be made • Presence of abiotic particles • reduce diffusive transport • increase sorptive capacity • Concentration of antimicrobial agent • higher doses than for planktonic • Species composition • co-culturing species improve resistance • Genetic makeup of the microbe-role remains unclear 41 5 Protective Mechanisms Defense mechanisms No/slow growth zones VBNC cells 42 • Persister cells: subpopulation of microbes with genetic characteristics that allow their survival when exposed to an antibiotic without undergoing genetic change; type of dormant cell • involves a metabolic shutdown not a genetic mutation 43 Multicellular Characteristics of Biofilms Contribute to Bacterial Survivability within a Biofilm 44