Microbiology is the branch of biology that focuses on the study of microorganisms and their relationship to disease processes by describing their characteristics (e.g., species, structure, virulence factors, etc.). In the 20th century, infectious diseases were the most significant causes of morbidity and mortality. After the advent of antibiotics, these diseases became significantly less prevalent and less deadly. They are, however, still encountered in clinical practice, so a competent physician must have a good grasp of the most common pathogens in their area of work.