This may be the toughest level opening in this episode. Jump at the machine gun and fight it out.

Push the walls by the wooden barrels in the south-eastern corner to get into the confusing vine section. The Gold Key is hidden inside it, but the mutants are everywhere.
Make it to the central room to get the Silver Key, then head on towards the north-east and reenter the vine section. Soon you will locate the elevator.

There are two 1-ups to be found.