Elimination of adhering bacteria from surfaces by pulsed laser beams

As an alternative to the use of chemicals for cleaning and disinfecting surfaces of equipment in food industry, the efficacy of pulsed laser beams for removal and killing of adherent bacteria from stainless steel surfaces was assessed. Escherichia coli biofilms were produced under dynamic conditions in diluted nutritive medium incubated at 37 degrees C for 24 h. Influence of energy density and number of shots were tested at three wavelengths (1064, 532 and 355 nm). With one 20 ns pulse, results range from 3.5 decimal reductions of the microbial load with < or = 50 MW cm-2 without visible alteration of the surface, to more than 6 decimal reductions with < or = 600 MW cm-2. The measured effect was largely attributed to removal of the micro-organisms and transfer to the surrounding air. The treatment could therefore be improved with respect to the numbers remaining associated with the surface by venting.