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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 LR max 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.

The current state of knowledge about hygiene (efficacy testing) in commercial dishwashers will be collated in this review. Therefore, studies about hygiene in commercial dishwashing are summarised and existing standards, guidelines and the legislative basis described. Finally, examples of information available from the market, for example, detergents are presented. The use of bioindicators contaminated with bovine albumin, mucin, corn starch and Enterococcus faecium is widely established in studies, which was the basis for the introduction of standards. Standards prescribe minimum temperatures for cleaning and rinsing, and most of them provide microbiological testing methods. A worldwide standardized test method for hygiene in commercial dishwashers would guarantee the comparability of country-specific standards but procedures currently available would need great efforts to be unified. A definition of a specified hygiene target level on cleaned dish items would also be meaningful because a harmless level of microorganisms can be achieved with it regardless of the initial microbial count or the process used.

The aim of this study was to establish a simple model describing the microbial reduction of a cleaning process by only using physical parameters of a given cleaning process (time and temperature) together with microorganism-specific inactivation parameters. The \Microbiological Inactivation Equivalent (MIE) unit" representing the time-temperature integral of a dish treatment process for a specific microorganism was developed. Microbiological reduction in suspension and dishwasher tests was tested in parallel. The microorganism-specific inactivation parameters were adjusted by fitting the MIE units to the experimental reduction factors gained. The mean square deviation between reduction factors and MIE units calculated was on average < 1 (Enterococcus faecium: 0.87, Micrococcus luteus: 0.79) in suspension tests and 1.09 (Enterococcus faecium) and 1.03 (Micrococcus luteus) in dishwasher tests. The MIE model can be used as a simplified method to predict the hygienic performance of a specific cleaning process under well-defined conditions.