Medical Microbiology comprises and integrates the fields of immunology, bacteriology, virology, mycology, and parasitology, each of which has seen considerable independent development in the past few decades. The common bond between them is the focus on the causes of infectious diseases and on the reactions of the host to the pathogens. Although the advent of antibiotics and vaccines has certainly taken the dread out of many infectious diseases, the threat of infection is still a fact of life: New pathogens are constantly being discovered; strains of „old" ones have developed resistance to antibiotics, making therapy more and more difficult; incurable infectious diseases (AIDS, rabies) are still with us.