Outdoor food bowl safety

I have two large stainless steel food bowls that I recently purchased for feeding a small group of ferals. Prior to the bowls, I had been feeding them on concrete, but the vet suggested that I use bowls instead after two of the ferals mysteriously passed away about a month ago and no clear cause could be ascertained.

The problem is, I've observed that other animals such as possums and raccoons seem to also be attracted to the food and will sometimes feed on it. As such, I don't like using the bowls since they're certain to be contaminated with those other animals' saliva. Of course, the concrete is sure to be as well, but that is a method of feeding that my dad had used for years until he passed away last summer. (I inherited feeding duty.)

Do any of you have a similar problem? Do you worry about it or ignore it? Do you have some sort of aggressive sterilization regimen? It hardly seems reasonable that I should bleach the bowls every single day or anything. I have to wonder if I'm over-thinking this as being a problem when it doesn't really present a significant danger.

I imagine the raccoons and possums were eating off the concrete, too.  The advantage of the bowls is that they can be washed - preferably in the dishwasher.  If you have two sets, you can switch them out.

And yes, I know, the things we do for our pets!