CONTROL OF FLOW-GENERATED BIOFILMS WITH SURFACTANTS Evidence of Resistance and Recovery

he action of cetyltrimethyl ammonium bromide (CTAB) and sodium dodecyl sulphate (SDS), a cationic and an anionic surfactant respectively, were investigated for their ability to control turbulent and laminar flow-generated biofilms formed byP. fluorescens. The disinfectant action of CTAB and SDS on biofilms was assessed by respiratory activity, variation of mass and structure, immediately, 3, 7 and 12 h after the application of the surfac-tants. Laminar flow-generated biofilms were more susceptible to the action of CTAB than those formed under turbulent flow. Total inactivation of the cells within the biofilms was not achieved for either type of flow-generated biofilms. For SDS, higher concentrations pro-moted significant biofilm inactivation, for both turbulent and laminar flow-generated biofilms. CTAB and SDS application did not promote the detachment of biofilms from the surfaces. Post-surfactant treatment, biofilms recovered respiratory activity, in some cases, reaching values higher than those found without chemical treatment. After CTAB treatment, the recov-ery of respiratory activity was not affected by the hydrodynamic conditions. Conversely, tur-bulent flow-generated biofilms showed a higher potential to recover their metabolic activity than laminar flow-generated biofilms, when previously challenged with SDS. Concerning bio-film mass, no significant variation (increase or decrease) was detected after 12 h of surfactant treatment. This study shows that care is needed when selecting the correct procedure and agent for biofilm control and demonstrates the influence of hydrodynamic conditions on the persistent and recalcitrant properties of P. fluorescens biofilms