Bacillus spores and moulding with TTC agar:: a useful method for the assessment of food processing equipment cleanability

In the present work a powerful and practical method for the assessment of food processing equipment clean-ability is described. Surfaces were soiled with Bacillus spores. After cleaning, surfaces were overlaid with agar containing a tetrazolium salt (TTC) which stained the growing colonies red. Stained colonies could be readily detected and counted. The poorer hygienically designed areas were easily observed and contamination levels could be defined. The TTC method was compared to other classical techniques such as contact plates, direct epifluorescence microscopy (DEM) and Shapton and Hindes (SH) agar. Recovery of bacteria using the TTC method was found to be a good complement to DEM and more accurate than contact plates and SH agar. Cleanability tests on closed equipment are also reported showing the utility of the TTC method.