How do i isolate a in p=a+b+c?

How do you isolate gram positive rods from gram negative rods?

• I used MacConkey to isolate gram negative because of bile salts inhibiting gram positive...how do I isolate gram positive rods?

• Answer:

  try replica plating. The colonies that grow on the MacConkey are gram negative, right? Well the ones that don't would be gram positive right? http://en.wikipedia.org/wiki/Replica_plating