Robert Koch (1843–1910)

Heinrich Hermann Robert Koch was a researcher from Germany who studied the causative agents of infectious diseases in various parts of Europe, Africa, and Asia during the late nineteenth and early twentieth centuries. Koch developed what researchers call Koch’s postulates, which are four criteria designed to establish whether a bacterium causes a certain disease, and as of 2025, many researchers still use Koch’s postulates to guide their research. He also received the Nobel Prize in Physiology or Medicine for his discovery of Mycobacterium tuberculosis, which is the bacterium responsible for tuberculosis, an infectious disease that primarily attacks the lungs. Koch’s research on identifying disease-causing bacteria for various infectious diseases has advanced disease prevention and treatment, especially for tuberculosis, which has the ability to transmit from mother to child.

1. Early Life and Education
2. Early Professional Life
3. Koch's Postulates
4. Impact

Early Life and Education

Koch was born on 11 December 1843 in a town in the Upper Harz Mountains called Clausthal, Germany, to Mathilde Juliette Henriette Biewend and Hermann Koch. Koch’s father was a mining engineer and had thirteen children of which Koch was the third. According to his Nobel Prize biography, Koch astounded his parents by teaching himself how to read at the age of five using only newspapers. He attended the local high school in Clausthal and studied biology there until his graduation in 1862.

From 1862 to 1866, Koch studied medicine and researched infectious diseases at the University of Göttingen in Göttingen, Germany, under Friedrich Gustav Jacob Henle, the university’s Professor of Anatomy. Henle was a physician who researched anatomy and infectious diseases in Germany. According to the Nobel Prize biography, Henle’s previous 1840 publication Von den Miasmen und Kontagion (On Miasmas and Contagions and on the Miasmatic-Contagious Diseases), in which he shared his belief that microscopic organisms cause infection, influenced Koch’s interest and work with infectious diseases. While Koch worked in Henle’s lab, the pair studied the connection between bacteria and disease. After graduating with a medical degree in 1866, Koch traveled to Berlin, Germany, to study chemistry.

Koch spent the late 1860s and early 1870s continuing his study of medicine, building a family, and gaining experience as a doctor in various German cities. After a six-month period of studying and research in Berlin, in 1867, Koch began his medical career in Hamburg, Germany, where he worked as an assistant in the city’s general hospital. Later that same year, he moved to Langenhagen, Germany, where he began working in general medicine. Also in 1867, Koch married his childhood friend, Emmy Adolfine Josephine Fraatz, and in 1868, they had their first and only child, a daughter named Gertrude. In 1869, Koch and his family moved to Rackwitz, Germany, where he passed his District Medical Officer’s Examination. After he moved to Rackwitz, the Franco-Prussian War began, and he volunteered in the war as a field hospital physician from 1870 to 1871.

Early Professional Life

In 1872, Koch moved to Wollstein, which as of 2025, is Wolsztyn, Poland, where he worked as a district medical officer and began studying anthrax. Anthrax is an infectious disease that can cause a wide range of symptoms including fever, nausea, swelling, shortness of breath, and potential death. Anthrax spreads through spores, which naturally occur in soil worldwide and commonly infect wild animals and livestock. The anthrax spores can spread to humans through cuts or injuries on the skin, inhalation, or ingestion. In the 1870s, the scientific community knew that animals with anthrax had a rod-shaped bacterium, later called Bacillus anthracis, present in their bodies. However, scientists did not understand the method of anthrax transmission or whether B. anthracis was the cause of the disease. Koch sought to answer those questions in his work.

During the mid-1870s, Koch confirmed that B. anthracis is the causative agent of disease. He initially began studying the disease in his at-home laboratory with a microscope. In 1876, he proved that a single pathogen, B. anthracis, triggers anthrax. Additionally, Koch discovered that anthrax goes through a series of phases called the anthrax life cycle. He recognized that the pathogen has a dormant phase, during which the pathogen produces rounded spores and is resistant to harsh environmental and adverse conditions, such as extreme weather changes. He identified that when conditions were favorable again, the spores could reproduce and spread the disease to animals through soil, which explained why many livestock died of anthrax in the 1870s. According to the Robert Koch Institute, Koch became the first to prove that a specific bacterial microorganism caused a specific disease.

Koch’s discoveries about anthrax and its causative bacterium garnered attention in the scientific community, and as a result, he received various publication opportunities throughout the remainder of the 1870s. In 1876, Koch presented his work on anthrax to Ferdinand Cohn, a researcher and professor of botany at the University of Breslau, which as of 2025, is the University of Wroclaw, located in Wroclaw, Poland, as well as Julius Cohnheim, a professor of pathological anatomy also at the University of Breslau. According to the Nobel Prize website, Koch’s worked impressed Cohn and Cohnheim, and they helped him publish his work in the Beiträge zur Biologie der Pflanzen (Contributions to the Biology of Plants), a botanical journal of which Cohn was the editor. Koch then continued his research on pathogens, and in 1878, he published a book called Über die Aetiologie der Wundinfectionskrankheiten (Investigations of the Aetiology of Wound Infections), in which he described that bacteria infect wounds.

From 1880 to 1883, Koch began developing techniques to create pure bacteria cultures and stain bacteria with dye at the Imperial Health Department in Berlin. In 1880, the local government in Berlin appointed him as a member of the Imperial Health Department, which was a public health laboratory at the time. Koch used the resources he received from the government to culture pure bacteria cultures, which grow in the absence of other bacterial species to prevent contamination. He also explored ways to stain, detect, and identify bacteria and microorganisms under a microscope and found that he could apply dyes to stain bacteria, allowing him to see their structure and form and study them more clearly.

During the early 1880s, Koch also experimented with tuberculosis and identified its causative pathogen, called tubercle bacillus or Mycobacterium tuberculosis. Koch identified the bacterium he suspected caused tuberculosis and concluded that tuberculosis spread through bodily fluids. According to Steve Blevins, a professor at the University of Oklahoma Health Sciences Center in Oklahoma City, Oklahoma, Koch’s findings on tuberculosis transmission caused medical professionals to recognize the disease as a public health problem and implement sterilization techniques of clothes and bedding in hospitals and other medical care facilities. In 1882, Koch announced his discovery of M. tuberculosis at the Berlin Institute for Physiology in Berlin and published his work. His findings in tuberculosis created the foundation for his postulates, or ideas regarding the causation of specific bacteria on specific diseases.

In 1883, the German government sent Koch to Egypt to study the cholera disease outbreak and appointed him the leader of the German Cholera Commission. Cholera is an acute bacterial infection caused by the ingestion of food or water contaminated with the bacterium Vibrio cholerae, and it causes symptoms such as diarrhea and dehydration. By 1896, cholera had killed over 58,000 people in Egypt. According to Blevins, the German government had concerns about the potential spread of cholera to Europe, so they sent a group of researchers, including Koch, to Egypt to study the disease. Through their work in Egypt, Koch and his colleagues learned that cholera spreads through contaminated water, and they were some of the first researchers to characterize the disease. Based on their findings, Koch proposed that the governments should increase nationwide water purification to prevent further spread.

Koch's Postulates

Through his experiments with anthrax, tuberculosis, and cholera in the mid- to late-1800s, Koch developed criteria, called Koch’s postulates, for determining whether a certain bacterium causes a disease. Koch built his postulates using the foundation established by his previous mentor Henle and developed his postulates alongside his assistant Friedrich Loeffler, a researcher who studied bacteria in Germany. Two years after reporting his findings with tuberculosis, in 1884, he published a definitive paper explaining that M. tuberculosis causes tuberculosis and outlining his postulates. Although Koch was developing his postulates in the 1880s, he did not publish a finalized version of his postulates until 1890. As of 2025, many researchers continue to widely accept Koch’s postulates.

Koch’s postulates contain four main ideas, which serve as guidelines for establishing that specific bacteria cause specific diseases. His first postulate states that the same causative organism must be present in every case of the disease, which means that in all cases of a disease that researchers encounter, the bacteria that they suspect is the cause of the disease must be present. The second postulate asserts that researchers must be able to isolate the organism and grow it into a pure culture. The third postulate explains that lab-grown culture must cause disease in a susceptible animal, meaning if scientists grow a bacterial culture in the lab, it must be able to infect an otherwise healthy animal with the disease in question. Finally, the fourth postulate states that after infection, the same bacteria present in the original infected organism must be present in the newly infected organism. According to Koch’s postulates, if a bacterium meets all four requirements, researchers can definitively link a specific bacterium to a specific disease.

From 1885 to 1890, leaders in Berlin awarded Koch with various job opportunities and recognitions. For example, in 1885, Koch received a job as Professor of Hygiene and Director of the Institute of Hygiene at the University of Berlin. Then, in 1890, the government in Berlin appointed him as the Surgeon General, a senior rank in medical military service. During that same year, the city of Berlin awarded him the title of Freeman of the City, a special honor that the city gives to honor individuals in Berlin.

In 1891, Koch began teaching as an Honorary Professor of the Medical Faculty of Berlin and acting as the Director of the Institute for Infectious Diseases, where he furthered his research on tuberculosis and began looking for treatment for the disease. His research led him to develop a serum from tubercule bacilli that he called tuberculin, which he claimed could cure the disease. However, according to the Nobel Prize website, Koch exaggerated the abilities of the serum, and he could not prove the serum had any healing properties.

In 1896, Koch traveled to South Africa to research rinderpest, which is a highly contagious and deadly disease that infects cattle, buffalo, and other cloven-hoofed animals. Rinderpest, also known as cattle plague, causes animals to suffer from symptoms such as fever, diarrhea, and oral sores. Koch was unable to identify the cause of rinderpest. However, in 1897, he proposed that people could prevent further spread of the disease by giving healthy animals a vaccine containing small amounts of bile from the gallbladders of infected cattle.

After conducting research in South Africa, Koch traveled to many other countries across the world to study infectious diseases between 1897 and 1904. First, he went to India and to parts of Africa to study diseases including malaria, a mosquito-borne parasitic disease that causes flu-like symptoms, and blackwater fever, a complication of malaria that causes red blood cells to burst. In 1898, he published his observations of those diseases and then went to Italy and the tropics to research a malaria treatment called quinine. Although Koch expanded his research to many different diseases, he continued his work on tuberculosis during his travels and discovered that different bacteria cause human and bovine tuberculosis. In 1901, he presented that conclusion at the International Medical Congress on Tuberculosis, a conference where scientists from different countries met in London, England, to discuss scientific advancements with tuberculosis. In 1904, Koch traveled to German East Africa to study the East Coast fever of cattle, which is a tick-borne disease commonly affecting cattle.

Koch encountered controversy in his life as many scientists accused him of criticizing others in the field and making false claims about his work. For example, Koch claimed that the serum he developed for the treatment of tuberculosis, tuberculin, could cure the disease. However, he could not prove the curative properties of the serum, which garnered doubt surrounding his credibility as a researcher. In addition, Koch criticized the work of Louis Pasteur, a researcher in France who was responsible for the creation of many vaccines, including vaccines for anthrax and rabies, which is a disease often transmitted by animal bites that can cause flu-like symptoms such as fever or weakness. Koch and Pasteur attempted to discount each other’s achievements, but their rivalry led to accomplishments that changed the scientific view of disease. Both scientists contributed to the germ theory of disease, which is the idea that microorganisms known as pathogens, or germs, cause disease. As of 2025, the scientific community has been reevaluating one of Koch’s main achievements, Koch’s postulates, because although Koch proposed that they applied to all diseases, researchers have since found some diseases that do not fit all four postulates Koch outlined in his work.

Impact

Through his research, Koch was one of the first people to identify that microorganisms cause diseases, and that advancement led to other developments with infectious disease. His suggestion that measures such as increasing sanitation and hygiene could help slow the spread of different diseases like anthrax, tuberculosis, and cholera remain relevant, as of 2025. Two of Koch’s students studying disease transmission, Emil von Behring and Paul Ehrlich, used his ideas to discover a treatment for diphtheria, a disease caused by a bacterial infection that can cause weakness and a sore and swollen throat. Additionally, Koch’s findings allowed for future research on tuberculosis, including research about the transmission of tuberculosis from mother to child through umbilical veins. In 1905, the Nobel Foundation awarded Koch the Nobel Prize in Physiology or Medicine for his discovery of the bacteria that causes tuberculosis.

Koch died on 27 May 1910 in Baden-Baden, Germany.

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