Extra Space in Category List

Hi,

I’m using some standard PHP to output the Category List below each post title.

I’ve tried two different lines of code to output this:
<span class="cat-links">Category:<?php printf(get_the_category_list(',') ) ?></span>
and
<span class="cat-links">Category:<?php the_category(', '); ?></span>

However, when a post is in two categories, both codes output an extra space before the comma that separates the categories. So it looks like this:

This post is in: Category 1 , Category 2

Could someone tell me what they think might be going on? Thanks!