A model system for evaluating surface disinfection in dairy factory environments

A model system was developed for evaluating the efficacy of disinfectants for inactivating bacteria present in biofilms on surfaces within dairy factory environments. Mixed culture biofilms of six dairy factory isolates (pseudomonads, coliforms and presumptive staphylococci) were generated on factory floor tiles and subjected to up to three fouling and cleaning (FC) cycles. Disinfectants (hypochlorite, peroxyacetic acid-, acid anionic- and quaternary ammonium compound (QUAT)-based products) were applied after cleaning at the supplier's recommended concentrations. Bacterial groups were enumerated using selective agar media. All disinfectants significantly (p <0.05) reduced surface counts of the three bacterial groups. The peroxyacetic acid-based product applied at 3.0% (v/v) achieved the greatest overall reductions in counts. In some cases, disinfectants were more biocidal towards particular bacterial groups. For example, hypochlorite demonstrated greater biocidal activity towards coliforms and staphylococci while the QUAT- and acid anionic-based disinfectants demonstrated greater biocidal activity towards staphylococci. The selective biocidal activity of hypochlorite and the acid anionic-based disinfectant was maintained over at least three FC cycles. The results demonstrate that disinfectants can alter the composition of the surface microflora and can be used to selectively reduce or eliminate particular bacterial groups from production environments. The model system was adapted to assess biofilm development and inactivation on a range of floor materials used in dairy factory environments. Clear differences were observed between surface materials at the end of the inoculation stage and following one FC cycle. For example, after one FC cycle, the highest bacterial counts were obtained for extruded floor tiles and the lowest for stainless steel and the polyurethane surface coating. The model system is versatile and there is scope to employ it to investigate a range of factors influencing the efficacy of cleaning and disinfection procedures towards biofilms. In addition, other microorganisms, such as pathogenic bacteria, may be added to the model biofilm and the influence of disinfectants on these investigated.