Golden Age of Microbiology
The Golden Age of Microbiology
Pasteur’s work with swan neck flasks ushered in the Golden Age of Microbiology. Within 60 years (1857-1941), a number of disease-causing microbes were discovered, great strides in understanding microbial metabolism were made, and techniques for isolating and characterizing microbes were improved.
Scientists also identified the role of immunity in preventing disease and controlling microbes, developed vaccines, and introduced techniques used to prevent. infection during surgery.
Recognition of the Relationship between Microorganisms and Disease
Although Fracastoro and a few others had suggested that invisible organisms produced disease, most believed that disease was due to causes such as supernatural forces, poisonous vapors called miasmasn, and imbalances among the four humors thought to be present in the body. The role of the four humors (blood, phlegm, yellow bile [choler], and black bile [melancholy]) in disease had been widely accepted since the time of the Greek Physician Galen (129-199). Support for the idea that microorganisms cause disease that is, the germ theory of disease – began to accumulate in the early nineteenth century. Agostino Bassi (1773-1856) first showed a microorganism could cause disease when he demonstrated in 1835 that a silkworm disease was due to a fungal infection. He also suggested that many diseases were due to microbial infections. In 1845, M.J. Berkeley proved that the great Potato Blight of Ireland was caused by a water mold, and in 1853, Heinrich de Bary showed that smut and rust fungi caused cereal crop diseases. Following his successes with the study of fermentation, Pasteur was asked by the French government to investigate the pebrine disease of silkworm that was disrupting the silk industry. After several years of work, he showed that the disease was due to a protozoan parasite. The disease, was controlled by raising caterpillars from eggs produced by healthy moths.
Indirect evidence for the germ theory of disease came from the work of the English surgeon Joseph Lister (1827-1912) on the prevention of wound infections. Lister, impressed with Pasteur’s studies on the involvement of microorganisms in fermentation and putrefaction, developed a system of antiseptic surgery designed to prevent microorganisms from entering wounds. Instruments were heat sterilized, and phenol was used on surgical dressings and at times sprayed over the surgical area. The approach was remarkably successful and transformed surgery after Lister published his findings in 1867. It also provided strong indirect evidence for the role of microorganisms in disease because phenol, which kills bacteria, also prevented wound infections.
Koch’s Postulates
The first direct demonstration of the role of bacteria in causing disease came from the study of anthrax by the German physician Robert Koch (1843-1910). Koch used the criteria proposed by his former teacher, Jocob Henle (1809-1885), to establish the relationship between Bacillus anthracis and anthrax, and published his findings in 1876 (Techniques & Applications briefly discusses the scientific method). Koch injected healthy mice with material from diseased animals, and the mice became ill. After transferring anthrax by inoculation through a series of 20 mice, he incubated a piece of spleen containing the anthrax bacillus in beef serum. The bacilli grew, reproduced, and produced endospores. When the isolated bacilli or their spores were injected into mice, anthrax developed. His criteria for proving the casual relationship between a microorganism and a specific disease are known as Koch’s postulates. Koch’s proof that B. Anthracis caused anthrax was independently confirmed by Pasteur and his coworkers. They discovered that after burial of dead animals, anthrax spores survived and were brought to the surface by earthworms. Healthy animals then ingested the spores an became ill.
Although Koch used the general approach described in the postulates during his anthrax studies, he did not outline them fully until his work on the cause of tuberculosis (table). In 184, he reported that this disease was caused by a rod-shaped bacterium, Mycobacterium tuberculosis; he was awarded the Nobel Prize in Physiology or Medicine in 1905 for his work. Koch’s postulates quickly became the cornerstone of connecting many diseases to their causative agent. However, their use is at time not feasible. For instance, some organisms, like Mycobacterium leprae, the causative agent of leprosy, cannot be isolated in pure culture.
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