Grant privileges on a number of databases containing the same prefix.
The tricky part is to take care of the right quotes to use, in particular the backtick ( ` )
Syntax is then as follows:
GRANT ALL ON `wordpress_%`.* TO ‘user’@’localhost’ IDENTIFIED BY ‘longasspassword’;
ALL can be, of course whichever required from SELECT DELETE INSERT….. .
Also use a strong password generator, like http://strongpasswordgenerator.com/ is much better then anything you could come up with.