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Robert Koch
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Heinrich Hermann Robert Koch

(1843-12-11)11 December 1843
Clausthal, Kingdom of Hanover, German Confederation
Died 27 May 1910(1910-05-27) (aged 66)
Nationality German
Alma mater University of Göttingen
Known for Bacterial culture method
Koch's postulates
Germ theory
Discovery of anthrax bacillus
Discovery of tuberculosis bacillus
Discovery of cholera bacillus
Scientific career
Fields Microbiology
Institutions Imperial Health Office, Berlin
University of Berlin
Doctoral advisor Georg Meissner
Other academic advisors Friedrich Gustav Jakob Henle
Karl Ewald Hasse
Rudolf Virchow
Influenced Friedrich Loeffler

Heinrich Hermann Robert Koch ( kokh 11 December 1843 – 27 May 1910) was a German physician and microbiologist. As the discoverer of the specific causative agents of deadly infectious diseases including tuberculosis, cholera and anthrax, he is regarded as one of the main founders of modern bacteriology. As such he is popularly nicknamed the father of microbiology (with Louis Pasteur), and as the father of medical bacteriology. His discovery of the anthrax bacterium (Bacillus anthracis) in 1876 is considered as the birth of modern bacteriology. Koch used his discoveries to establish that germs "could cause a specific disease" and directly provided proofs for that germ theory of diseases, therefore creating the scientific basis of public health, saving millions of lives. For his life's work Koch is seen as one of the founders of modern medicine.

While working as a private physician, Koch developed many innovative techniques in microbiology. He was the first to use the oil immersion lens, condenser, and microphotography in microscopy. His invention of the bacterial culture method using agar and glass plates (later developed as the Petri dish by his assistant Julius Richard Petri) made him the first to grow bacteria in the laboratory. In appreciation of his work, he was appointed to government advisor at the Imperial Health Office in 1880, promoted to a senior executive position (Geheimer Regierungsrat) in 1882, Director of Hygienic Institute and Chair (Professor of hygiene) of the Faculty of Medicine at Berlin University in 1885, and the Royal Prussian Institute for Infectious Diseases (later renamed Robert Koch Institute after his death) in 1891.

The methods Koch used in bacteriology led to establishment of a medical concept known as Koch's postulates, four generalized medical principles to ascertain the relationship of pathogens with specific diseases. The concept is still in use in most situations and influences subsequent epidemiological principles such as the Bradford Hill criteria. A major controversy followed when Koch discovered tuberculin as a medication for tuberculosis which was proven to be ineffective, but developed for diagnosis of tuberculosis after his death. For his research on tuberculosis, he received the Nobel Prize in Physiology or Medicine in 1905. The day he announced the discovery of the tuberculosis bacterium, 24 March 1882, has been observed by the World Health Organization as "World Tuberculosis Day" every year since 1982.

Early life and education

Koch was born in Clausthal, Germany, on 11 December 1843, to Hermann Koch (1814–1877) and Mathilde Julie Henriette (née Biewend; 1818–1871). His father was a mining engineer. He was the third of thirteen siblings. He excelled academically from an early age. Before entering school in 1848, he had taught himself how to read and write. He completed secondary education in 1862, having excelled in science and math.

At the age of 19, in 1862, Koch entered the University of Göttingen to study natural science. He took up mathematics, physics and botany. He was appointed assistant in the university's Pathological Museum. After three semesters, he decided to change his area of study to medicine, as he aspired to be a physician. During his fifth semester at the medical school, Jacob Henle, an anatomist who had published a theory of contagion in 1840, asked him to participate in his research project on uterine nerve structure. This research won him a research prize from the university and enabled him to briefly study under Rudolf Virchow, who was at the time considered as "Germany's most renowned physician." In his sixth semester, Koch began to research at the Physiological Institute, where he studied the secretion of succinic acid, which is a signaling molecule that is also involved in the metabolism of the mitochondria. This would eventually form the basis of his dissertation. In January 1866, he graduated from the medical school, earning honours of the highest distinction, maxima cum laude.


After graduation in 1866, Koch briefly worked as an assistant in the General Hospital of Hamburg. In October that year he moved to Idiot's Hospital of Langenhagen, near Hanover, as a general physician. In 1868, he moved to Neimegk and then to Rakwitz in 1869. As the Franco-Prussian War started in 1870, he enlisted in the German army as a volunteer surgeon in 1871 to support the war effort. He was discharged a year later and was appointed as a district physician (Kreisphysikus) in Wollstein in Prussian Posen (now Wolsztyn, Poland). As his family settled there, his wife gave him a microscope as a birthday gift. With the microscope, he set up a private laboratory and started his career in microbiology.

Koch began conducting research on microorganisms in a laboratory connected to his patient examination room. His early research in this laboratory yielded one of his major contributions to the field of microbiology, as he developed the technique of growing bacteria. Furthermore, he managed to isolate and grow selected pathogens in a pure laboratory culture. His discovery of the anthrax bacillus (later named Bacillus anthracis) hugely impressed Ferdinand Julius Cohn, professor at the University of Breslau (now the University of Wrocław), who helped him publish the discovery in 1876. Cohn had established the Institute of Plant Physiology and invited Koch to demonstrate his new bacterium there in 1877. Koch was transferred to Breslau as district physician in 1879. A year after, he left for Berlin when he was appointed a government advisor at the Imperial Health Office, where he worked from 1880 to 1885. Following his discovery of the tuberculosis bacterium, he was promoted to Geheimer Regierungsrat, a senior executive position, in June 1882.

In 1885, Koch received two appointments as an administrator and professor at Berlin University. He became Director of Hygienic Institute and Chair (Professor of hygiene) of the Faculty of Medicine. In 1891, he relinquished his professorship and became a director of the Royal Prussian Institute for Infectious Diseases (now the Robert Koch Institute) which consisted of a clinical division and beds for the division of clinical research. For this he accepted harsh conditions. The Prussian Ministry of Health insisted after the 1890 scandal with tuberculin, which Koch had discovered and intended as a remedy for tuberculosis, that any of Koch's inventions would unconditionally belong to the government and he would not be compensated. Koch lost the right to apply for patent protection. In 1906, he moved to East Africa to research a cure for trypanosomiasis (sleeping sickness). He established the Bugula research camp where up to 1000 people a day were treated with the experimental drug Atoxyl.

Scientific contributions

Techniques in bacteria study

Robert Koch made two important developments in microscopy; he was the first to use an oil immersion lens and a condenser that enabled smaller objects to be seen. In addition, he was also the first to effectively use photography (microphotography) for microscopic observation. He introduced the "bedrock methods" of bacterial staining using methylene blue and Bismarck (Vesuvin) brown dye. In an attempt to grow bacteria, Koch began to use solid nutrients such as potato slices. Through these initial experiments, Koch observed individual colonies of identical, pure cells. He found that potato slices were not suitable media for all organisms, and later began to use nutrient solutions with gelatin. However, he soon realized that gelatin, like potato slices, was not the optimal medium for bacterial growth, as it did not remain solid at 37 °C, the ideal temperature for growth of most human pathogens. And also many bacteria can hydrolyze gelatin making it a liquid. As suggested to him by his post-doctoral assistant Walther Hesse, who got the idea from his wife Fanny Hesse, in 1881, Koch started using agar to grow and isolate pure cultures. Agar is a polysaccharide that remains solid at 37 °C, is not degraded by most bacteria, and results in a stable transparent medium.

Development of Petri dish

Koch's booklet published in 1881 titled "Zur Untersuchung von Pathogenen Organismen" (Methods for the Study of Pathogenic Organisms) has been known as the "Bible of Bacteriology." In it he described a novel method of using glass slide with agar to grow bacteria. The method involved pouring a liquid agar on to the glass slide and then spreading a thin layer of gelatin over. The gelatin made the culture medium solidify, in which bacterial samples could be spread uniformly. The whole bacterial culture was then put in a glass plate together with a small wet paper. Koch named this container as feuchte Kammer (moist chamber). The typical chamber was a circular glass dish 20 cm in diameter and 5 cm in height and had a lid to prevent contamination. The glass plate and the transparent culture media made observation of the bacterial growth easy.

Koch publicly demonstrated his plating method at the Seventh International Medical Congress in London in August 1881. There, Louis Pasteur exclaimed, "C'est un grand progrès, Monsieur!" ("What a great progress, Sir!") It was using Koch's microscopy and agar-plate culture method that his students discovered new bacteria. Friedrich Loeffler discovered the bacteria of glanders (Burkholderia mallei) in 1882 and diphtheria (Corynebacterium diphtheriae) in 1884; and Georg Theodor August Gaffky, the bacterium of typhoid (Salmonella enterica) in 1884. Koch's assistant Julius Richard Petri developed an improved method and published it in 1887 as "Eine kleine Modification des Koch’schen Plattenverfahrens" (A minor modification of the plating technique of Koch). The culture plate was given an eponymous name Petri dish. It is often asserted that Petri developed a new culture plate, but this was not so. He simply discarded the use of glass plate and instead used the circular glass dish directly, not just as moist chamber, but as the main culture container. This further reduced chances of contaminations. It would also have been appropriate if the name "Koch dish" had been given.


Robert Koch is widely known for his work with anthrax, discovering the causative agent of the fatal disease to be Bacillus anthracis. He published the discovery in a booklet as "Die Ätiologie der Milzbrand-Krankheit, Begründet auf die Entwicklungsgeschichte des Bacillus Anthracis" (The Etiology of Anthrax Disease, Based on the Developmental History of Bacillus Anthracis) in 1876 while working at in Wöllstein. His publication in 1877 on the structure of anthrax bacterium marked the first photography of a bacterium. He discovered the formation of spores in anthrax bacteria, which could remain dormant under specific conditions. However, under optimal conditions, the spores were activated and caused disease. To determine this causative agent, he dry-fixed bacterial cultures onto glass slides, used dyes to stain the cultures, and observed them through a microscope. His work with anthrax is notable in that he was the first to link a specific microorganism with a specific disease, rejecting the idea of spontaneous generation and supporting the germ theory of disease.


Aetiologie der Tuberkulose
Koch's drawing of tuberculosis bacilli in 1882 (from Die Ätiologie der Tuberkulose)

During his time as the government advisor with the Imperial Health Agency in Berlin in the 1880s, Koch became interested in tuberculosis research. At the time, it was widely believed that tuberculosis was an inherited disease. However Koch was convinced that the disease was caused by a bacterium and was infectious. In 1882, he published his findings on tuberculosis, in which he reported the causative agent of the disease to be the slow-growing Mycobacterium tuberculosis. He published the discovery as "Die Ätiologie der Tuberkulose" (The Etiology of Tuberculosis), and presented before the German Physiological Society at Berlin on 24 March 1882.

There was no particular reaction to this announcement. Eminent scientists such as Rudolf Virchow remained skeptical. Virchow clung to his theory that all diseases are due to faulty cellular activities. On the other hand, Paul Ehrlich later recollected that this moment was his "single greatest scientific experience."


Professors Koch and Pfeiffer working in a laboratory, invest Wellcome L0030175
Koch (on the microscope) and his colleague Richard Friedrich Johannes Pfeiffer (standing) investigating cholera outbreak in Bombay, India.

In August 1883, the German government sent a medical team led by Koch to Alexandria, Egypt, to investigate a cholera epidemic there. Koch soon found that the intestinal mucosa of people who died of cholera always had bacterial infection, yet could not confirm whether the bacteria were the causative pathogens. As the outbreak in Egypt declined, he was transferred to Calcutta (now Kolkata) India, where there was a more severe outbreak. He soon found that the river Ganges was the source of cholera. He performed autopsies of almost 100 bodies, and found in each bacterial infection. He identified the same bacteria from water tanks, linking the source of the infection. He isolated the bacterium in pure culture on 7 January 1884. He subsequently confirmed that the bacterium was a new species, and described as "a little bent, like a comma." His experiment using fresh blood samples indicated that the bacterium could kill red blood cells, and he hypothesized that some sort of poison was used by the bacterium to cause the disease. In 1959, Indian scientist Sambhu Nath De discovered this poison, the cholera toxin. Koch reported his discovery to the German Secretary of State for the Interior on 2 February, and published it in the Deutsche Medizinische Wochenschrift (German Medical Weekly) the following month.

Although Koch was convinced that the bacterium was the cholera pathogen, he could not entirely establish a critical evidence the bacterium produced the symptoms in healthy subjects (following Koch's postulates). His experiment on animals using his pure bacteria culture did not cause the disease, and correctly explained that animals are immune to human pathogen. The bacterium was then known as "the comma bacillus", and scientifically as Bacillus comma. It was later realised that the bacterium was already described by an Italian physician Filippo Pacini in 1854, and was also observed by the Catalan physician Joaquim Balcells i Pascual around the same time. But they failed to identify the bacterium as the causative agent of cholera. Koch's colleague Richard Friedrich Johannes Pfeiffer correctly identified the comma bacillus as Pacini's vibrioni and renamed it as Vibrio cholera in 1896.

Tuberculosis treatment and tuberculin

Koch gave much of his research attention on tuberculosis throughout his career. After medical expeditions to various parts of the world, he again focussed on tuberculosis from the mid-1880s. By that time the Imperial Health Office was carrying out a project for disinfection of sputum of tuberculosis patients. Koch experimented with arsenic and creosote as possible disinfectants. These chemicals and other available medications did not work. His report in 1883 also mentioned a failed experiment on an attempt to make tuberculosis vaccine. By 1888, Koch turned his attention to synthetic dyes as antibacterial chemicals. He developed a method for examining antibacterial activity by mixing the gelatin-based culture media with a yellow dye, auramin. His notebook indicates that by February 1890, he tested hundreds of compounds. In one of such tests, he found that an extract from the tuberculosis bacterium culture dissolved in glycerine could cure tuberculosis in guinea pigs. Based on a series of experiments from April to July 1891, he could conclude that the extract did not kill the tuberculosis bacterium, but destroyed (by necrosis) the infected tissues, thereby depriving bacterial growth. By November 1890, Koch was able to show that the extract was effective in humans as well. Many patients and doctors went to Berlin to get Koch's remedy. But his experiments showed that tuberculosis infected guinea pigs developed severe symptoms when the substance was inoculated. The severity was more so in humans. This development of severe immune response, which is now known to be due to hypersensitivity, is known as the "Koch phenomenon." The chemical nature was not known, and among several independent experiments done by the next year, only his son-in-law, Eduard Pfuhl, was able to reproduce similar results. It nevertheless became a medical sensation, and the unknown substance was referred to as "Koch's Lymph." Koch published his experiments in the 15 January 1891 issue of Deutsche Medizinische Wochenschrift, and The British Medical Journal immediately published the English version simultaneously. The English version was also reproduced in Nature, and The Lancet in the same month. The Lancet presented it as "glad tidings of great joy." Koch simply referred to the medication as "brownish, transparent fluid." Josephs Pohl-Pincus had used the name tuberculin in 1844 for tuberculosis culture media, and Koch subsequently adopted as "tuberkulin."

The first report on the clinical trial in 1891 was disappointing. By then 1061 patients with tuberculosis of internal organs and of 708 patients with tuberculosis of external tissues were given the treatment. An attempt to use tuberculin as a therapeutic drug is regarded as Koch's "greatest failure." With it his reputation greatly waned. But he devoted the rest of his life trying to make tuberculin as a usable medication. His discovery was not a total failure, the substance is today used for hypersensitivity test for tuberculosis patients.

Acquired immunity

Koch observed the phenomenon of acquired immunity. On 26 December 1900, he arrived as part of an expedition to German New Guinea, which was then a protectorate of the German Reich. Koch serially examined the Papuan people, the indigenous inhabitants, and their blood samples and noticed they contained Plasmodium parasites, the cause of malaria, but their bouts of malaria were mild or could not even be noticed, i.e. were subclinical. On the contrary, German settlers and Chinese workers, who had been brought to New Guinea, fell sick immediately. The longer they had stayed in the country, however, the more they too seemed to develop a resistance against it.

Koch's postulates

During his time as government advisor, Koch published a report on how he discovered and experimentally showed tuberculosis bacterium as the pathogen of tuberculosis. He described the importance of pure cultures in isolating disease-causing organisms and explained the necessary steps to obtain these cultures, methods which are summarized in Koch's four postulates. Koch's discovery of the causative agent of anthrax led to the formation of a generic set of postulates which can be used in the determination of the cause of most infectious diseases. These postulates, which not only outlined a method for linking cause and effect of an infectious disease but also established the significance of laboratory culture of infectious agents, became the "gold standard" in infectious diseases.

Although Koch worked out the principles, he did not formulate the postulates, which were introduced by his assistant Friedrich Loeffler. Loeffler, reporting his discovery of diphtheria bacillus in 1883, stated three postulates as follows:

1. The organism must always be present in every case of the disease, but not in healthy individuals.
2. The organism must be isolated from a diseased individual and grown in pure culture.
3. The pure culture must cause the same disease when inoculated into a healthy, susceptible individuals.

The fourth postulate was added by an American plant pathologist Erwin Frink Smith in 1905, and is stated as:

4. The same pathogen must be isolated from the experimentally infected individuals.

Personal life

In July 1867, Koch married Emma (Emmy) Adolfine Josephine Fraatz, and the two had a daughter, Gertrude, in 1868. Their marriage ended after 26 years in 1893, and later that same year, he married actress Hedwig Freiberg (1872–1945).

On 9 April 1910, Koch suffered a heart attack and never made a complete recovery. On 27 May, three days after giving a lecture on his tuberculosis research at the Prussian Academy of Sciences, Koch died in Baden-Baden at the age of 66. Following his death, the Institute named its establishment after him in his honour. He was irreligious.

Awards and honors

Robert Koch's name on the Frieze of LSHTM
Koch's name as it appears on the LSHTM frieze in Keppel Street, Bloomsbury, London
Statue of Robert Koch in Berlin
Statue of Koch at Robert-Koch-Platz (Robert Koch square) in Berlin

Koch was made a Knight Grand Cross in the Prussian Order of the Red Eagle on 19 November 1890, and was elected a Foreign Member of the Royal Society (ForMemRS) in 1897. In 1905, he was awarded the Nobel Prize in Physiology and Medicine "for his investigations and discoveries in relation to tuberculosis." In 1906, research on tuberculosis and tropical diseases won him the Order Pour le Merite and in 1908, the Robert Koch Medal, established to honour the greatest living physicians. Emperor Wilhelm I awarded him the Order of the Crown, 100,000 marks and appointment as Privy Imperial Councillor, Surgeon-General of Health Service, and Fellow of the Science Senate of Kaiser Wilhelm Society.

Koch established the Royal Prussian Institute for Infectious Diseases in Berlin 1891. After his death it was renamed Robert Koch Institute in his honour.

The World Health Organization observes "World Tuberculosis Day" every 24 March since 1982 to commemorate the day Koch discovered tuberculosis bacterium.

Koch's name is one of 23 from the fields of hygiene and tropical medicine featured on the frieze of the London School of Hygiene & Tropical Medicine building in Keppel Street, Bloomsbury.

A large marble statue of Koch stands in a small park known as Robert Koch Platz, just north of the Charity Hospital, in the Mitte section of Berlin. His life was the subject of a 1939 German produced motion picture that featured Oscar winning actor Emil Jannings in the title role. On 10 December 2017, Google showed a Doodle in celebration of Koch's birthday.

Koch and his relationship to Paul Ehrlich, who developed a mechanism to diagnose TB, were portrayed in the 1940 movie Dr. Ehrlich's Magic Bullet.

See also

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