Microbiology is the branch of biology concerned with the study of microorganisms. Microorganisms are classified in a number of ways. Classification is useful for empiric management of infection. Most microorganisms are made up of cells with the exception of viruses and prions. Parasitology: the scientific study of parasites. Virology: the scientific study of viruses. Mycology: the scientific study of fungi. Bacteriology: the scientific study of bacteria.