Hi,
Well, it hardly depends on how it exactly looks like in your case, but, you need to replace this
<div class='item'>
with something like:
<div class="item <?php echo $r->content_type == 'pagepost' ? ' ' . implode(' ', wp_get_post_categories($r->id, array('fields'=>'slug'))) : ''; ?>">
This may not work out of the box, but should be very close to a proper solution.