Food Microbiology - I
- History of Microbiology
- Theory of Spontaneous Generation
- Germ Theory of Disease
- Koch's Postulate
- Pure Culture Concept
- History of Microbiology
- Theory of Spontaneous Generation
- Germ Theory of Disease
- Koch's Postulate
- Pure Culture Concept
- History of Microbiology
- Theory of Spontaneous Generation
- Germ Theory of Disease
- Koch's Postulate
- Pure Culture Concept
Evolution
The germ theory of disease
Before Pasteur had proved by experiment that the bacteria are the causative agent of disease.
- Fracastoro suggested that disease might be due to invisible organism transmitted from one person to another.
- Von plenciz not only stated that living agent are the cause of disease but suspected that different germs were responsible for different disease.
- Wendell Holmes discovered that puerperal fever, a disease of child birth was contagious and it was caused by a germ carried from one mother to another by midwives and physician.
- Ignaz Philipp was suggesting the use of antiseptics in surgical practices. Childbirth death was reduced in the cases handled according to his instruction.ie, which minimize the chance of infection.
- Joseph Lister in England developed an antiseptic surgery to prevent the entry of microbes into the wound. He suggested that surgical instruments were sterilized and phenol was used as antiseptic. He also suggested that wash the hand and wearing a clean glove before surgery.
- Pasteur investigate pebrine, a silk worm disease and he found that protozoa was the causative agent. He also suggested a preventive method by the use of healthy caterpillars. He also investigated about anthrax causing microorganism.
Koch's Postulate
➢ The first demonstration of the role of bacteria in disease which is came from the study of anthrax by German physician Robert Koch.
➢ He discovered the typical bacilli with squarish end in the blood of cattle that had died by anthrax i.e., Bacillus anthraxis
➢ He grew these bacteria in a pure culture and examined microscopically and then injected them into other animal to see the development of anthrax.
➢ Again, he isolates the same anthrax causing bacteria from the experimentally infected animal.
➢ Finally, he proves the relationship between a microorganism and a specific disease.
➢ The series of observation leads to the establishment of Koch’s postulates, which provided the guidelines to identify the causative agent of an infectious disease.
Koch’s postulates are,
- A specific organism can always be found in association with a given disease and absent in healthy animal
- The suspected organism can be isolated and grown in pure culture
- The isolated organism will produce the same disease when inoculated into a healthy experimental animal.
- It is possible to recover or isolate the same suspected organism in pure culture from experimentally infected animal.
Contribution of Louis Pasteur
- He disproves the concept of spontaneous generation through swan neck experiment
- He found that fermentation of fruits and grains resulting alcohol was brought about by microbes and he also suggested that undesirable microbes can be removed by heating without destruction of flavor.
- He found that holding the juices at temp 62.8 c for 30 mints – the process is known as pasteurization
- Prepare a rabies vaccine for rabies virus.
Pure Culture Concept
If the bacterial species in high proportion of the mixed population then it can be isolated in pure culture as a single strain. A strain is made up of a succession of culture and is often derived from a single colony. if a strain derived from a single parent cell, it is termed a clone. A variety of techniques have been developed for the isolation into pure culture.
The streak plate method: streak plate technique is used for the isolation into pure culture of the organisms (mostly bacteria), from mixed population. A portion of the mixed culture is placed on the surface of an agar medium in a petri plate by using a loop and streaked across the surface. This procedure “thin out” the bacteria on the surface so that some individual bacteria are separated from each other. As the original sample is diluted by streaking it over successive quadrants, the number of organisms decreases. Usually by the third or fourth quadrant only a few organisms are transferred which will give discrete colony forming units (CFUs). During this procedure colony developing from one cell will not merge with another.
