Yes those letters are real. As Chris said staph is everywhere. Anywhere mold and midew grows, bacteria will be there competing for food.
Not all staph is created equal. Staph epidermatis is a normal bacteria that is on everyone's skin. It rarely causes problems and there is no reason to get rid of it unless you are headed into surgery. Most of the bacteria on our skin is protective. They compete with the bad actors like Methicillin resistant Staphalococcus aureas, knowm as MRSA. The overuse of antibacterial soaps have created the MRSA outbreaks we see today.
There have been many articles showing that playing in the dirt as a child is protective. In fact children who play in the dirt have fewer allergies as adults. One could make the arguement that potters should have a better immune system because of their clay exposure.
If someone brought samples of clay into my InstaCare I would love to do the testing. It would break my routine of colds, flues, broken bones. It could probably be written up as an interesting case study looking at what bacteria is found in ceramics and if pottery would be protective against bad bacteria like MRSA.
Although I have had a little old lady bring in over 100 jars of fecal material, so I could "examine it all." And yes Chris I did "have the nice young men in their clean white shirts come and take her away."