A surface populated by a bacteria capable of producing a biofilm is treated beneficially by contacting it with a substance having N-acyl homoserine lactone degradant activity obtained from the secretions and/or excretions of the larval form of the green bottle fly, Lucilia sericata. Furthermore, a synergistic effect is achieved when the larval secretions/excretions are used in combination with an antibiotic, e.g. tetracycline. Such a substance having N-acyl homoserine lactone degradant activity obtained from Lucilia sericata larval secretions and/or excretions also forms part of the invention.