If you mean PhD by Grad School then here are some of the programs:
Most of the programs have an Umbrella program where you rotate in 3 labs in the field of Molecular Biology and then choose the one you like the most so you can end up choosing Microbiology. They all provide full funding including stipend and health insurance regardless of your nationality:
1) http://www.med.ufl.edu/IDP/
2) http://dms.dartmouth.edu/mcb/
3) http://www.mcb.tulane.edu/finaid.html
4) http://www.uvm.edu/cmb/index.php
5) http://www.bioscience.utah.edu/
6) http://www.biochem.purdue.edu/grad/index.html
7) http://www.uiowa.edu/microbiology/graduate_education.shtml
8) http://biochemistry.umaryland.edu/Pages/support.aspx
GOOD LUCK!
