Action of a cationic surfactant on the activity and removal of bacterial biofilms formed under different flow regimes

This study investigates the antimicrobial activity of a cationic surfactant cetyltrimethylammonium bromide (ctab) on mature pseudomonas fluorescens biofilms, grown in either laminar or turbulent flow. the action of ctab was assessed by means of the biofilm respiratory activity and the loss of biofilm mass. the biofilm structure damage caused by ctab application was inspected using sem. the physical stability of the biofilm was evaluated through the variation of the mass of the biofilm after submission to a series of different rotation velocities. in order to characterize the variation in the susceptibility to the surfactant, the antimicrobial effect of ctab was also investigated with planktonic cells by measuring the bacterial respiratory activity and atp released, and the effect of a protein (bsa) as an interfering substance. the planktonic tests showed that ctab was bactericidal against p. fluorescens since it caused total bacteria inactivation for the higher concentrations tested. nevertheless, that bactericidal activity was significantly reduced when bsa was added to the suspended cultures. further results indicated that ctab also promoted the release of the intracellular atp. this leakage of intracellular component may be a sign of the disruption of the outer membrane of the bacteria emphasizing that, in some extent, membrane damage may account for, at least, the mode of antimicrobial action of this surfactant. concerning biofilm tests, ctab acted differently in biofilms formed under laminar and turbulent conditions: laminar biofilms were more susceptible to ctab than those formed under turbulent flow. however, total respiratory inactivation was not achieved in all situations tested, conversely to the planktonic situation, emphasizing the possible protective action of the polymeric matrix of the biofilm. furthermore, ctab appeared to cause little effect on the removal of biofilms from the metal surface. sem observations highlighted that the bacteria entrapped in the biofilm, after ctab application, seems to loose, in same extent, their typical morphological structure, which reinforces the atp results. the biofilm physical stability tests showed that only with the synergistic combination of higher surfactant concentrations and high shear forces was possible to achieve the most efficacious mean to promote biofilm detachment