I have installed mysql55-server using macports.
I can start the server successfully via:
$ sudo launchctl load -w /Library/LaunchDaemons/org.macports
MacPorts versions of MySQL disable networking using the skip-networking
setting by default to allow side-by-side installation of multiple versions of MySQL (which is possible when using sockets, but impossible with TCP ports).
Adjust your MySQL configuration file to enable networking. See also the output of port notes mysql55
.