Microbial Harboring Characteristics of Dishmachine-Filmed Glassware

Alkaline-earth type films, produced by detergent-water interactions, are frequently deposited on eating utensils during mechanical dishwashing. These films are aesthetically unacceptable but their public health significance and food spoilage potential have not been established. Sterile glass petri dishes were washed in an institutional-type dishmachine containing Bacillus subtilis spores in the washwater. A film-producing model system was developed to examine film formation in conjunction with spore deposition. The influence of three distinct detergent formulations on this association was also determined. Detergent formulations contained 6.75% phosphorus (P), as sodium tripolyphosphate (STP), 3.0% P as STP, a proprietary phosphate substitute, and the film-producing model formulation devoid of both STP and substitute water conditioning agents. Film deposition was quantified as μg Ca⁺⁺ per cm² by an acid rinse-atomic absorption spectrophotometric method. The quantity of B. subtilis spores recovered from washed petri dishes in the model system was related to film deposition. The relationship was dependent on the number of consecutive dishmachine cycles and the hardness of the water supply. Above a threshold value of 3 μg Ca⁺⁺ per cm², Ca⁺⁺ deposition and B. subtilis spore harborage were directly correlated. Both of these conditions were inhibited to varying degrees by the three detergent formulations. These data suggest that dishware filming may be cause for public health and food spoilage concerns.