wp_list_categories echo current or parent cat on single.php

found a solution here:
http://www.screenshine.net/blog/1474_wordpress-plugin-show-active-category

with the changed foreach-loop:

foreach (wp_get_post_categories($post->ID) as $catid) {
if (preg_match('#cat-item-' . $catid . '"#', $text)) {
$text = str_replace('cat-item-' . $catid . '"', 'cat-item-' . $catid . ' current-cat"', $text);
}
}