To confirm the importance of washing food sediments from the surface of food-related environments, we examined resistances against
benzalkonium chloride of pathogenic bacterial (
Escherichia coli O26,
Pseudomonas aeruginosa and
Staphylococcus aureus) cells dried and adhered on stainless steel dishes with milk, beef gravy or tuna gravy. Suspensions (0.1 ml) of these bacteria (8–9 log cfu/ml) were put on a 5 cm
![phi phi](http://www.sciencedirect.com/scidirimg/entities/3d5.gif)
stainless steel dish and dried at room temperature (20–24 °C) for 90 min in a bio-clean bench with ventilation. Though these bacteria suspended with distilled water decreased 30–40 fold during the drying period, milk and the gravies protected the bacteria. Without the food elements, the adhered
E. coli and
Stap. aureus were decreased from 6 to<2 log cfu/dish by 0.5 mg/ml
benzalkonium chloride (BKC) for 10 min treatment. Although
Ps. aeruginosa showed resistance to BKC, the adhered cells were inactivated by 2.0 mg/ml BKC. However, the bactericidal effect disappeared by the food elements, particularly with milk, even at 1.0 and/or 2.0 mg/ml BKC levels. The protective efficiency of milk on bacteria disappeared if washed with water.