Categories in Page Title

At the moment I have this code for my title

<title><?php if(is_home() || is_search()) { bloginfo('name'); echo ' - '; bloginfo('description'); } else { wp_title('') ;} ?></title>

If I have a sub category I would like both the sub category and it’s parent category in the title. The code above will not display the parent category only the sub category which in my case leaves out important keywords in the title.

Any suggestion on how I can fix this?

Thanks.