Problems Including File

Yes, you can use a /wp-content/mu-plugins folder for

  • single file
  • autoloading

plugins. The only thing you will have to do is to use a plugin header comment in this file:

<?php /* Plugin Name: I am a MU-Plugin */

Then you will find a link on top of your /wp-admin/plugins.php page that says

“Must-Use Plugins”

where you will find the list of mu-plugins. Those plugins can not be deactivated by an administrator or anyone else — only someone having access to your servers filesystem will be able to deactivate them by removing them from this folder.

Note, that plugins residing in subdirectories in this folder will not get loaded.