Remember that Miller columns are tree structures, so taking a look to Apple's Finder (which actually uses a form of Miller columns) would provide you with a tested answer. I'm not at the office so I can't access a Mac to take a screenshot, but you can do it by yourself.
On a more specific subject, I think you should highlight only the searched term and nothing else. If I look for "foo", I won't care about "foo parent", "foo grandparent" and "foo dinosaurs father of them all foo". At least not on the beginning, because I'm literally looking for FOO. If I need to go down the tree branches, I can do it.
But don't highlight things I didn't request for, or you'll force me to scan data I didn't ask for until I find what I needed. And I won't know what to do with the other highlighted terms (should I click them? Is there something hidden? Maybe hover over it?)
Finally, the breadcrumb. Remember that last node in a breadcrumb is the one you're currently on. However, you're listing the whole tree branches visualized on the current page, which is really confusing for a breadcrumb. In this specific case, and barring testing, I think the back button should be more than enough for navigation purposes.
A middle point between Miller columns and breadcrumbs would be that after search, you show only the column where the searched term is. Then, a breadcrumb above showing the whole trail to get to that search term