Keltin is absolutley corect. The mold and mildew found on the sandwhiches and thicker fries could grow because of the moisture content contained in those foods. The thin fries at places like McDonald's and Burger King have had the natural moisture of the potatoe replaced by grease. The salt also inhibits the growth of microscopic organizms. Have you ever noticed that honey never molds? The same thing is taking place in that natural substance. It is in fact a hypo-tonic solution and molds/mildews cannot survive in it.
Jerkeys, pemican, and a host of foods have been dried, smoked, and salted to curb the growth of micro-organizms for centuries to keep them from spoiling. I would submit that potato chips would behave identically to the Micky-D's fries.
Now I'm not saying that the McDonald's french fries are not bad for your health. They contain little if any nutritional value and are choked full of fat and starches. In other words, they are the foods described as empty calories. They don't help your body, but rather, stress it, along with white flour, and other highly processed foods. That is where the danger in eating them really lies. They fill you and give you nothing good for your body.
Seeeeeya; Goodweed of the North