In the recent years, many individuals started to purchase dishwashers aiming for reducing time, efforts and money compared to the conventional (manual) dishwashing. Proper dishwashing is essential for removing pathogenic microorganism that can accumulate on the dishes when leaved for a long period without washing. Such organism can progress to infection if not removed properly and can be fatal in vulnerable populations in particular, children, old aged, immunocompromised, ..etc. Though, you may wonder how much efficacy that the dishwasher has, to remove or at least decrease the bacterial load? In this article we will report you with the most recent published papers regarding this topic.
The antimicrobial activity of the dishwashers depends on several parameters (1):
1-Thermal inactivation: High temperature plays an important role in reducing or killing microorganisms.
2-Chemical inactivation: Many dishwashing detergents had an antimicrobial activity.
3-Mechanical removal: The contact among water, detergent and dishes inside the dishwasher is essential for microorganisms’ removal. Moreover, the speed of the spray arms and the water pressure comes from it could introduce further strong mechanical removal.
4-Time: Long dishwashing cycles with long contact time of the dishes with water, detergent and high temperature increases the efficacy of the antimicrobial role of the dishwasher.
Real experiment to determine the factors affecting the microbial reduction:
Brands and colleagues used the dishwasher (GSL-2, Miele & Cie. KG, G€utersloh) to test the factors that affect the microbial reduction on two main microbes: Micrococcus luteus or Entereococcus faecium (2).
-The higher the temperature of the cycle, the higher microbial reduction that can be achieved. Furthermore, in short cycles, the highest reduction of microbes was achieved when the temperature reached 60°C or higher.
-The longer the duration cycle, the higher microbial reduction that can be achieved. However, this factor became of low efficacy if detergent was not added to the cycle.
–The usage of detergent played an important role in reducing the microbial load than no detergent used. However, when using a high temperature 70°C or higher, the reduction was the same when using the detergent versus no detergent.
What are the microorganisms that can be found in the dishwashers’ sump water and the interior wall?
According to the results of Brands and colleagues (3), the sump water of the dishwasher had high number of bacterial load rather than the interior wall.
The common organisms were:
1-Yeasts and Mouldes
2-Black Yeasts
3-Enterobacteriaceae
4-Lactose Fermenting Enterobacteriacea
What is the place of dishwasher that had the highest microbial load?
Brands and colleagues compared three types of dishwashers (4):
1-Standard dishwasher without water reservoir or any hygienic measures
2-Standard dishwasher with water reservoir and hygienic measures
3-A commercially available dishwasher with water reservoir
After running 77 cycles:
The highest microbial load was found in the water reservoir followed by the sump of the commercial dishwasher.
However, in the standard dishwasher with water reservoir and additional hygienic measures, the sump had more microbial load than the reservoir.
Read also: Effortless Dishwasher Care: Learn How to Add Rinse Aid Like a Pro for Sparkling Results
🡺Despite that some dishwashers had water reservoir to reduce the water consumption. This reservoir could be some sort of danger when having a quite high microbial load.
What is the maximum time to leave your dishes unclean with in the dishwasher before running it?
Many dishwashers are available in the market with high capacity to load many items. Though, many households may wait from one day to several days waiting for the complete filling of the dishwasher as it consumes energy, water and detergent. So at the end of the month, the bills will come at high cost, therefore, they wait for the maximum filling. Although, there is no guideline about the maximum time to leave your dishes unclean inside the dishwasher. It is advisable to run the dishwasher as soon as you load the dishwasher with your cooking items. By doing this, you prevent the bacterial replication on your cooking items and facilitate the dishwasher job by removing those pathogens.
References:
- Struchtrup SS, Esmarch-Rummler Bv, Stamminger R. Hygiene in Commercial Dishwashing–A Review about the State of Knowledge in Research, Standardization, Regulation and Market Information. Tenside Surfactants Detergents. 2021;58(5):320-33.
- Brands B, Schulze Struchtrup S, Stamminger R, Bockmühl DP. A method to evaluate factors influencing the microbial reduction in domestic dishwashers. Journal of applied microbiology. 2020;128(5):1324-38.
- Brands B, Honisch M, Merettig N, Bichler S, Stamminger R, Kinnius J, et al. Qualitative and quantitative analysis of microbial communities in household dishwashers in Germany. Tenside Surfactants Detergents. 2016;53(2):112-8.
- Brands B, Bockmühl DP. Experimental evaluation of hygienic conditions in domestic dishwashers. Tenside Surfactants Detergents. 2015;52(2):148-54.