Fundamentals of Microbiology

1.1.1.2 Germ theory of Disease

Agostino Bassi, in 1835 was the first one to demonstrate that microorganism cause disease (silk-work disease – by fungi). In 1867, Joseph Lister, Father of antibiotic surgery introduced antibiotic principles in surgical practice. He used carbolic acid as antiseptic. The first direct demonstration of the role of bacteria in causing anthrax disease was by the German Physician Robert Koch (1843 – 1910) (Anthrax caused by Bacillus anthracis). His criteria for providing casual relationship between a microorganism and a specific disease are known as Koch’s postulates:

1. The microorganism must be present in very case of the disease but absent from healthy host
2. The suspected microorganism must be isolated and grown in a pure culture
3. The same disease must result when the isolated microorganism is inoculated into a healthy host
4. The same microorganism must be isolated again from the experimentally diseased host

Robert Koch also developed the techniques required to grow bacteria on solid media and to isolate pure culture of pathogenic microorganisms. He first tried to grow bacteria on sterile surfaces of cut, boiled potatoes. He then used gelatin to solidify liquid medium. However, the media liquefied when temperature exceeded 28^oC. Fannie Eilshemius Hesse suggested the use of agar as a solidifying agent in culture media. Agar has several advantages:

• Agar is not digested by most bacteria
• Agar remains solid until temperature reaches above 98^oC and medium solidifies at around 44^oC

  One of Koch’s assistants, Richard Petri developed the Petri dishfor cultivation of bacteria Vaccination was successfully used against smallpox by Edward Jenner in 1798. He administered cowpox virus to protect individuals against smallpox virus.

  Elie Metchnikoff discovered some blood leucocytes that could engulf disease causing bacteria. He called these cells as phagocytes and the process phagocytosis.

  Winogradsky (1856 – 1953) and Beijerinck (1851 – 1931) investigated the ecological role of microorganisms and revealed the role of microorganisms in carbon, nitrogen and sulphur cycles. They developed the enrichment – culture technique and the use of selective media, which have been of great importance in microbiology.

  Development of microbiology in the twentieth century in close relationship with other biological disciplines like genetics and biochemistry contributed to the rise of molecular biology – the branch of biology dealing with the physical and chemical aspects living matter and its function.