i have an irrational fear of the bacteria that live on sponge.
Hot take: there is no food safety reason to replace a sponge if it’s still good at removing food from dishes. If you remove the food source, and the soap removes whatever is living on the dish, whatever is left over will die due to lack of nutrients and water. It’s why in food safety courses you are taught that dishes have to dry completely. Even a sponge which has been used once will be depositing “new” pathogens onto the dish. Stuff is gonna live in the sponge. The sponge doesn’t kill pathogens. Removal, soap, and desiccation do. The sponge’s job is almost purely mechanical.
There is absolutely a food safety reason to replace a sponge. Most bacteria don’t just die when they’re in dry nutrient poor environments. They desiccate themselves into a spore form. Those spores can stay like that for very long periods of time until their environment becomes more wet. Then they can continue their lifecycle until they dry out again. Dry doesn’t mean sterile.
Old sponges are smelly as shit though.
New sponges have an unnaturally nice chemical smell.