Installing Fedora packages (or for that matter any packages not built for - in this case - EL6) is never recommended, and as you have discovered, unlikely to work.
As CentOS-6 supplies MySQL 5.1.52-1.el6_0.1 so you are outside of supported territory. Where did you get 5.5.18? I see packages from Atomic and Remi of that version.
You will need to get or build
a package compatible with your MySQL version.
If more help is needed then please provide more information about your system
and package versions.