According to several sources I found online, including this one:
http://www.gpc.edu/~janderso/historic/psmeanin.htmthe Greek -ktistos suffix means "to establish." If you look up Saint Theoctistus, you can find links that say San Teotisto, so your connection seems to be correct as I suspected it would be, but the proof was hard to find as he was a minor saint. I should have searched for the Latinized spelling of Theoktistos earlier. It would have saved me a lot of time. :-)
~~~~~~~~~~~Amanda~~~~~~~~~~~