The color scheme in this piece of work is brilliant. The background colors aren't as saturated as the foreground, which makes the main two characters pop. Excellent touch.
Your use of shading is done very effectively to show the 3-dimensional aspect of the artwork.
You have a great idea, the sandwich fighting off the germ. It's very creative; I'm assuming you got inspired while eating a sandwich.
I only thing that I think could be improve is the sandwiches face. It would be better if his face was more INTENSE. After all, he is fighting a germ that is trying to ruin his deliciousness.
I really love this piece, I hope to see more from you. :P