Microbiology refers to the study of microorganisms, whether they are bacteria, viruses, fungi, etc. Knowledge of their genetic heritage, their behaviors and interactions with their environment is useful to understand how they operate and what their impact on multicellular organisms might be.
Bacteriology is the science that focuses on bacteria and their properties. Many tests exist in bacteriology, for example, to measure the effect of antibiotics, to study the mechanism of action of antibacterial molecules or to test the synergy between bacteria and other microorganisms.
Virology refers to the study and usage of viruses. In this context, various experiments are possible, such as the production of viruses or the evaluation of the antiviral effect of a molecule.