Variable in wp_list_categories

Hey ;/

I need to use a variable inside a wp_list_categories command..

i am using this code:

$catout = get_category_by_slug('featured');
$id = $catout->term_id;
echo '<ul>';
wp_list_categories('hide_empty=0&title_li=&depth=1&exclude=(here i need the $id var)');
echo '</ul>';

Would apreciate your help plz