The antibacterial efficacy of Norwegian hand dishwashing detergents

The antibacterial efficacy of the standard and antibacterial variants of Zalo, the leading name brand hand dishwashing detergent in Norway, was investigated by a variety of techniques. Tests were chosen to simulate possible applications of the detergents that were expected to have relevance to kitchen hygiene. According to the manufacturer, the antibacterial detergent is designed for use as a bacterial inhibitor in cloths, sponges and brushes. This claim was investigated by inoculating commercially available kitchen sponges with test strains and detergent and then determining the number of cells surviving this treatment. The antibacterial formulation significantly reduced (> 4 log) numbers of both Gram negative bacteria and by staphylococcus aureus, whereas Gram negative bacteria increased by approximately equal numbers in control sponges (no detergent) and in sponges containing the standard version of the detergent. The standard detergent reduced the numbers of Staphylococcus aureus by > 2 log.The Mle of each formulation was determined by the pour plate technique, and growth curves (suspension tests) in broth containing detergents were generated for culture collection strains and for a bacterial population present in dishwashing water. Both analyses showed that the antibacterial product was usually the most efficacious. Pseudomonas aeruginosa was able to grow on a minimal agar medium including either detergent as a sole source of carbon and energy. P. aeruginosa was subcultured at least 10 times on minimal medium containing detergent over a period of about 2 months. In addition, Salmonella Typhimurium and P. aeruginosa were grown in tryptone soya broth containing the antibacterial detergent for 15 generations over a similar time period. Neither treatment had an effect on bacterial antibiotic resistance.