Hi, I'm in the process of getting mine as well. A rep from Mayo's legal team will email you at some point to request for some documents (including your visa screen certificate) so I suggest you get that done asap, especially if you're not planning on paying for the expedited service. When you're filling the CGFNS application there's a portion that includes specialist certification so I guess that's where your microbiology certification goes. Then you complete the rest of the tasks and order. I'm a generalist so I didn't have to fill the specialty option but if in doubt you could always call CGFNS