Microbial methods for assessment of cleaning and disinfection of food-processing surfaces cleaned in a low-pressure system

An assessment system using various microbial methods was developed for the detection of residual, surface-attached microbes and soil on surfaces after sanitation. The microbial methods tested were: conventional cultivation, m icroscopy using image analysis after staining with acridine orange (AO), 5- cyano-2,3-ditolyl tetrazolium chloride/4', 6-diamidino-2-phenylindole (CTC- DAPI) and LIVE/DEAD stains, impedance measurements, viable counts with 2,3, 5-triphenyltetrazolium chloride (TTC) agar and ATP measurements. A test rig was used for the trials with four different low-pressure cleaning procedur es (pressure <20 bar flow rate 271 min(-1)). A strong alkaline foam cleaner , Trippel, and a mild alkaline foam cleaner, Topax 12, in combination with two disinfectants, respectively, were used. The disinfectants were peroxide -peracetic-acid-based Oxonia Aktiv and potassium-persulphate-based Virkon. Conventional cultivation combined with impedance measurements and image ana lysis of surfaces stained with AO, as well as CTC-DAPI, gave results that w ere comparable and complementary. The combination of these methods enabled a total evaluation of both the removal of biofilm and the killing of bacter ial cells. The low-pressure cleaning system did not remove all of the bacte rial cells from the surfaces and did not kill the bacteria even after use o f the strong alkaline foam cleaner. The above-mentioned protocol carried ou t on the test rig can also be used to evaluate the sensitivity of microbial methods for use in certain industrial premises.