[Marco van Herwaarden]

After you have created the database, you can (if i remember correct with Plesk, i try to avoid using it ) also add a new database user (think on the page you get after creating the database). Add a new user for each database and set the permissions (not sure if this is needed with plesk) for the user/database.

PS There is a manual topic on using plesk to create a database: Setting-up a MySQL Database in Plesk