Does Dishwashing Kill Bacteria?

Dishwashers vs. Hand Washing

To measure the levels of bacteria left after hand washing dishes, Microbiologist Craig Andrew-Kabilafkas of Australian Food Microbiology tested 25 kitchen sponges and found that more than half contained considerable levels of contamination, including high concentrations of E. coli and staphylococcus aureus. Andrew-Kabilafkas observed that using a dishwasher at very high temperatures would kill 99.9 percent of bacteria. The tap water temperature in most residential kitchens is between 86 and 104 degrees Fahrenheit, but E. coli can survive at temperatures up to 111.2 degrees Fahrenheit. However, the hot temperature setting on dishwashers is at least 154 Fahrenheit.

Other Views

Good Housekeeping conducted a similar study that involved sponges used by a test group of consumers as well as lab sponges infected with bacteria. The study determined that microwaves and dishwashers killed more than 99 percent of bacteria in the sponges. Conversely, other studies have found that dishwashers don’t necessarily top the 154 degree threshold required for killing germs. CBS News warns against putting dirty sponges in a dishwasher because the water temperature cannot be verified and bacteria that is not killed will taint the rest of the dishwasher’s contents. However, the dishwasher’s drying cycle appears to be an effective way to kill bacteria.

Salmonella

To address concerns regarding the possible hazards of giving raw meat to pets, the National Center For Biotechnology Information conducted a study involving food bowls containing raw meat contaminated with salmonella. These bowls were emptied and placed in a dishwasher for cleaning, and the researches were surprised by the results. Salmonella is not considered thermotolerant -- meaning it is thought to be susceptible to high temperatures. However, dishwashing temperatures of 185 degrees Fahrenheit were “minimally effective at eliminating salmonella contamination.”

Antibacterial Dishwashing Detergent

Antibacterial dishwashing detergent is marketed as an agent that kills germs, but that claim is not regulated by the Environmental Protection Agency. Regular and dishwasher antibacterial detergents are classified by their manufacturers as hand soaps -- personal hygiene products -- and are under the jurisdiction of the Food and Drug Administration. However, the FDA has no system in place for testing a product’s antibacterial effectiveness, so there is no way to validate or repudiate the manufacturers’ claims.