A new technique for the performance evaluation of clean-in-place disinfection of biofilms

A concentric cylinder reactor (CCR) is described that enables the steady-state kinetics of microbial biofilms to be evaluated under conditions of constant nutrient flow and variable shear-stress. The reactor has been used to evaluate the influence of fluid dynamic shear on the extent and mode of detachment of bacteria from biofilms. Using a food factory isolate of Pseudomonas aeruginosa, a general increase in the overall growth rate and detachment of the biofilms (cfu cm⁻² min⁻¹) with time was shown for each biofilm, regardless of the prevailing shear. As the shear rate was increased beyond 0.123 ms⁻¹, populations tended toward a pseudo steady-state. Sudden changes in shear force, however, caused dramatic changes in the productivity of steady-state populations. The CCR provides an effective means of testing disinfectant activity, particularly for clean-in-place situations, and allows for an examination of the residual effects of a cleansing programme on a treated surface for three different chemical classes of disinfectant. Utilisation of the CCR would, therefore, provide enhanced ability to determine the efficacy and efficiency of chemical products for use in sanitation protocols.