germteorien

Germ theory is the idea that many diseases are caused by microorganisms—bacteria, viruses, fungi, and parasites—that invade the body and disrupt normal function. It contrasts with earlier miasma theory, which attributed illness to foul air or imbalances in the body's humors.

Historical development includes early notions of contagion dating to Girolamo Fracastoro in the 16th century, who proposed that tiny seeds could transmit disease. In the 19th century, Louis Pasteur's experiments linked microbes to fermentation and demonstrated that sterilized environments without microbial life remained free of growth, undermining spontaneous generation. The same era saw Joseph Lister apply antisepsis to surgery, dramatically reducing infections. Robert Koch later established a direct link between specific microbes and particular diseases, identifying Bacillus anthracis in anthrax and Mycobacterium tuberculosis in tuberculosis, and formulating Koch's postulates to prove causation.

Koch's postulates state that the microorganism must be found in diseased hosts and not healthy ones, be isolated in pure culture, cause disease when introduced into a healthy host, and be re-isolated from the newly diseased host. These criteria provided a practical standard for proving causation, though they are not universally applicable. Limitations include pathogens that cannot be cultured, multifactorial diseases, and the role of host susceptibility. With viruses and prions, molecular methods and genetic evidence are used to establish causation alongside or instead of conventional culture-based postulates.

Impact and legacy: Germ theory transformed medicine and public health. It underpins aseptic surgical techniques, sanitation, vaccination, and the development of antibiotics. Modern microbiology expands germ theory with insights into microbiota, virology, and molecular biology, recognizing that many diseases involve complex interactions among hosts, pathogens, and environments.