THE EFFECT OF SILVER IONS AND CHLORINE ON THE SURVIVAL OF STAPHYLOCOCCUS AUREUS AND BACILLUS CEREUS IN DISHWATER

摘要

This paper investigates the effect of chlorine and silver ion solutions on the survival of Bacillus cereus (vegetative phase) and Staphylococcus aureus in batch cultures, representing dishwater. Dishwater contains organic matter and bacteria and bacterial activities are partly reduced by high pH (11-12) and temperature (55-65℃) in professional and domestic dishwashers. In manual dishwashing, temperature and pH are kept lower (45℃ and pH 7), which is less sufficient for the reduction of bacteria. In a broth, organic loaded in order to mimic dishwater, solutions of Ag~+ or hypochlorite were added at 45 ℃ and pH 7 and samples were withdrawn for a period of 40 minutes. 1 ppm Ag~+ was required to obtain a 1 to 2 log unit reduction of B. cereus and S. aureus in 10 minutes. An addition of 160 ppm hypochlorite reduced B. cereus and S. aureus by 4 log units in two minutes, whereas 16 ppm of hypochlorite had no effect on the survival of S. aureus. The level of free residual chlorine varied with the COD value of the cultured solutions. We found that both silver and hypochlorite can be used as antibacterial agents in dishwater. The disadvantage with the use of hypochlorite is that the COD value determines the antibacterial effect. Using Ag~+ solutions to reduce bacteria has the drawback that they are toxic to water-living organisms and are considered to develop Ag4 resistant bacteria. To reduce the risk of cross-contamination from dishwater to dishware high temperature and detergent with high pH is to be preferred.