Your Dishwasher is Probably a Petri Dish
From Wikipedia: a Petri dish is named after the German bacteriologist Julius Richard Petri, is a shallow cylindrical glass or plastic lidded dish that biologists use to culture cells – such as bacteria – or small mosses.
So that being said/typed, is your dishwasher an over-sized Petri dish?
I recently posted about things you need to clean oftener than once a year, and oddly enough dishwashers were left off of that list. They're one of those appliances (like a microwave) that you'd think basically cleans itself. Soap + hot water = clean, right?
Microbiologists refer to dishwashers as "extreme environments." Hot to cold, wet to dry, basic to acidic; it makes for an "extreme habitat" that only allows the extremist microbes to survive.
But here's the thing: they're not likely to actually hurt you.
"The risk [of getting sick] is probably in the realm of a shark attack." ~ Erica Hartmann, assistant professor at Northwestern University
If you or someone in your house has a weakened immune system, then you should worry about keeping your dishwasher clean.