Are mattress covers required on motel mattresses?

you can purchase mattress covers in all major department stores and others like bed, bath and beyond

Always!

Pour a bottle of white vinegar in your washer & wash as extra Or, if your mattress can tolerate it, dampen the area, then rub a generous amount of baking soda and salt (as salt is an abrasive)...

Hopefully you don't.

Put it in the washer, add detergent, and run it.