A method to evaluate factors influencing the microbial reduction in domestic dishwashers.

AIMS: To develop a method that is able to determine the microbial reduction in different dishwasher cleaning cycles and differentiate between different program parameters used. METHODS AND RESULTS: Stainless steel biomonitors were contaminated with Micrococcus luteus or Entereococcus faecium and cleaned in a specially programmed household dishwasher with different cleaning temperatures and durations. No detergent, bleach-free detergent or detergent containing activated oxygen bleach was used. The logarithmic reduction (LR) was determined. The microbial reduction depended on the cleaning temperature, the duration of the cleaning cycles and the detergent type used. LR increased with higher temperatures, longer cleaning cycles and use of detergent. CONCLUSIONS: The factors cleaning cycle temperature, cleaning cycle duration, final rinsing temperature and the use of detergent all contributed to the reduction of test-strains in dishwasher cycles. A combination of longer dishwashing cycles and increased temperatures resulted in LRmax of the microbial load. SIGNIFICANCE AND IMPACT OF THE STUDY: Cycles in domestic appliances are very diverse; therefore a standardized method to determine their ability to reduce the microbial load is of great use. The method described here is able to demonstrate the reductions achieved by dishwashing cycles with different parameters and might help to find the necessary balance between energy saving and an acceptable level of hygiene.

Impact of wash cycle time, temperature and detergent formulation on the hygiene effectiveness of domestic laundering.

AIMS: Investigation of the effect of temperature and duration of the laundering process with and without activated oxygen bleach (AOB)-containing detergent on the hygienic effectiveness of laundering. METHODS AND RESULTS: Cotton test swatches were contaminated with Staphylococcus aureus, Enterococcus hirae, Pseudomonas aeruginosa, Candida albicans and Trichophyton mentagrophytes and were washed in a household washing machine using temperatures between 20 and 60°C and different wash cycle times. The logarithmic microbial reduction factor and cross-contamination (i.e. transfer from contaminated to sterile swatches) were used to indicate the hygienic effectiveness of the washing process. For all tested micro-organisms, the temperature needed for decontamination depended on washing time and detergent type. Hygiene effectiveness of laundering was enhanced by inclusion of AOB even at lowest temperatures, except for C. albicans, which was virtually unaffected by AOB. The use of AOB-containing detergents as well as high washing temperatures reduced cross-contamination to sterile swatches included in the load. CONCLUSIONS: Depending on the type of organism, longer wash cycle times or the use of AOB-containing detergents can be used to enhance the hygiene effectiveness of laundering. SIGNIFICANCE AND IMPACT OF THE STUDY: The study demonstrates that it is possible to compensate for the loss of hygiene effectiveness of laundering at lower temperatures using detergents with activated oxygen bleach or by extending the wash cycle time.