Medicine microbiology is a branch of medical science concerned with the prevention, diagnosis and treatment of infectious diseases. There are four kinds of microorganisms that cause infectious disease: bacteria, fungi, parasites and viruses, and one type of infectious protein called prion. A medical microbiologist studies the characteristics of pathogens, their modes of transmission, mechanisms of infection and growth. Microbiologists study microbial pathology; some study common, non-pathogenic specie. Microbiology primarily focuses on the presence and growth of microbial infections in individuals, their effects on the human body and the methods of treating those infections.