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-st ate kinetics of microbial biofilms to be evaluated under conditions of cons tant 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 det achment of bacteria from biofilms. Using a food factory isolate of Pseudomo nas aeruginosa, a general increase in the overall growth rate and detachmen t 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 beyon d 0.123 ms(-1), populations tended toward a pseudo steady-state. Sudden cha nges in shear force, however, caused dramatic changes in the productivity o f steady-state populations. The CCR provides an effective means of testing disinfectant activity, particularly for clean-in-place situations, and allo ws for an examination of the residual effects of a cleansing programme on a treated surface for three different chemical classes of disinfectant. Util isation of the CCR would, therefore, provide enhanced ability to determine the efficacy and efficiency of chemical products for use in sanitation prot ocols.