" mpm-itk allows you to run each of your vhost under a
separate UID and GID - in short, the scripts and configuration
files for one vhost no longer have to be readable for all the other
vhosts. mpm-itk works with mod_php because mpm-itk is based on the
traditional prefork MPM, which means it's non-threaded. This means
you don't need to use suExec or suPHP anymore to run a website's
PHP scripts as a separate user."