WORLD OF MICROBIOLOGY AND IMMUNOLOGY Koch, Robert327•
cultivating disease-producing bacteria and to formulate strate-
gies for preventing their spread. In 1881 he published a report
advocating the importance of pure cultures in isolating dis-
ease-causing organisms and describing in detail how to obtain
them. The methods and theory espoused in this paper are still
considered fundamental to the field of modern bacteriology.
Four basic criteria, now known as Koch’s postulates, are
essential for an organism to be identified as pathogenic, or
capable of causing disease. First, the organism must be found
in the tissues of animals with the disease and not in disease-
free animals. Second, the organism must be isolated from the
diseased animal and grown in a pure culture outside the body,
or in vitro. Third, the cultured organism must be able to be
transferred to a healthy animal, which will subsequently show
signs of infection. And fourth, the organisms must be able to
be isolated from the infected animal.
While in Berlin, Koch became interested in tuberculosis,
which he was convinced was infectious, and, therefore, caused
by a bacterium. Several scientists had made similar claims but
none had been verified. Many other scientists persisted in
believing that tuberculosis was an inherited disease. In six
months, Koch succeeded in isolating a bacillus from tissues of
humans and animals infected with tuberculosis. In 1882, he
published a paper declaring that this bacillus met his four con-
ditions—that is, it was isolated from diseased animals, it was
grown in a pure culture, it was transferred to a healthy animal
who then developed the disease, and it was isolated from the
animal infected by the cultured organism. When he presented
his findings before the Physiological Society in Berlin on
March 24, he held the audience spellbound, so logical and thor-
ough was his delivery of this important finding. This day has
come to be known as the day modern bacteriology was born.
In 1883, Koch’s work on tuberculosis was interrupted
by the Hygiene Exhibition in Berlin, which, as part of his
duties with the health department, he helped organize. Later
that year, he finally realized his dreams of travel when he was
invited to head a delegation to Egypt where an outbreak of
cholera had occurred. Louis Pasteur had hypothesized that
cholera was caused by a microorganism; within three weeks,
Koch had identified a comma-shaped organism in the intes-
tines of people who had died of cholera. However, when test-
ing this organism against his four postulates, he found that the
disease did not spread when injected into other animals.
Undeterred, Koch proceeded to India where cholera was also
a growing problem. There, he succeeded in finding the same
organism in the intestines of the victims of cholera, and
although he was still unable to induce the disease in experi-
mental animals, he did identify the bacillus when he exam-
ined, under the microscope, water from the ponds used for
drinking water. He remained convinced that this bacillus was
the cause of cholera and that the key to prevention lay in
improving hygiene and sanitation.
Koch returned to Germany and from 1885–1890 was
administrator and professor at Berlin University. He was
highly praised for his work, though some high-ranking scien-
tists and doctors continued to disagree with his conclusions.
Koch was an adept researcher, able to support each claim with
his exacting methodology. In 1890, however, Koch falteredfrom his usual perfectionism and announced at the
International Medical Congress in Berlin that he had found an
inoculum that could prevent tuberculosis. He called this agent
tuberculin. People flocked to Berlin in hopes of a cure and
Koch was persuaded to keep the exact formulation of tuber-
culin a secret, in order to discourage imitations. Although opti-
mistic reports had come out of the clinical trials Koch had set
up, it soon became clear from autopsies that tuberculin was
causing severe inflammationin many patients. In January
1891, under pressure from other scientists, Koch finally pub-
lished the nature of the substance, but it was an uncharacteris-
tically vague and misleading report which came under
immediate criticism from his peers.
Koch left Berlin for a time after this incident to recover
from the professional setback, although the German govern-
ment continued to support him throughout this time. An
Institute for Infectious Diseases was established and Koch was
named director. With a team of researchers, he continued his
work with tuberculin, attempting to determine the ideal dose
at which the agent could be the safest and most effective. TheRobert Koch, whose postulates on the identification of
microorganisms as the cause of a disease remain a fundamental
underpinning of infectious microbiology.womi_K 5/6/03 3:29 PM Page 327