Cook rotini in boiling salted water until firm, but not quite tender, 6 to 7 minutes; drain and set aside.
Brown sausage on both sides in a large saucepan; remove from pan, reserving dripping.
Add mushrooms, green pepper, onion and butter to sausage drippings; cook over medium heat 3 minutes.
Stir in flour, salt and dry mustard.
Gradually blend in milk; cook over medium heat, stirring constantly, until thickened.
Stir in cheeses and Worcestershire sauce; continue cooking until cheeses melt.
Mix in sausage and rotini.
Divide mixture between two greased 2-quart baking dishes; bake in preheated 350° F oven about 30 to 40 minutes.
Serve hot.
Servings: 10