Principles of Microbiology (Full Course-One Semester) This video covers the principles of microbiology. Microbiology is the study of microorganisms, which are unicellular or cell-cluster microscopic organisms. This includes eukaryotes such as fungi and protists, and prokaryotes, which are bacteria and archaea. Viruses, though not strictly classed as living organisms, are also studied. Microbiology is a broad term which includes virology, mycology, parasitology and other branches.