Assuming you already have an ssh key pair for each account and you are using that ssh private key to sign commits, you can manage the different accounts by configuring git to use a different configuration profile based on the directory under which you are cloing the repository.
For each key pair (account) you will create a config file that will apply to all the projects under that account's work directory.
/Users/robandpdx/
|__.gitconfig
|__.gitconfig.work
|__.gitconfig.personal
|__github-work/ # <--- This is where you will clone all your work repositories