DISCOVERY OF THE MICROBIAL WORLD

• Microbiology is the science dealing with the study of organisms that are individually too small to be seen by the naked eye which includes bacteria, fungi, viruses and protozoa.
• Microbiology is the study of microbes.
• Individual microbes can be observed only with the use of various types of microscopes.
• The two major categories of microbes are acellular microbes, also called infectious particles, which include viruses and prions, and cellular microbes, also called microorganisms.
• Even before microorganisms were seen, some investigators suspected their existence and responsibility for disease.
• The Roman philosopher Lucretius and the physician Girolamo Fracastoro suggested that disease was caused by invisible living creatures.
• The earliest microscopic observations appear to have been made between 1625 and 1630 on bees and weevils by the Italian Francesco Stelluti, using a microscope supplied by Galileo.
• About 1674, the invisible world of microorganism was discovered by the Dutch merchant Anton van Leeuwenhoek.
• Leeuwenhoek was a Dutch merchant who used hand lenses to inspect the quality of cloth.
• Leeuwenhoek was inspired by Hooke’s Micrographia, and so he developed the skill of grinding lenses.
• Using only a single lens, no larger than a pinhead that magnified objects 200 x, Leeuwenhoek was able to observe animalcules.
• The biggest sort of animalcules had a very strong and swift motion, and shot through the water like a pike.
• The second sort of animalcules often spun around like a top and were far more in number.
• Leeuwenhoek was suspicious and secretive and did not share his method of grinding of lenses, therefore, no one could challenge his findings.
• Leeuwenhoek sent numerous drawings describing in detail to the Royal Society of London.
• The emergence of experimental science provided a means to test long held beliefs and resolve controversies.
• In the early 1600s, most naturalists were “vitalists,” individuals who thought life depended on a mysterious “vital force” that pervaded all organisms.
• The last quarter of the nineteenth century was a time of great activity that resulted in an impressive number of exciting discoveries.
• Frannie Eilshemius Hesse (1850 - 1934) was the first to propose the use of agar to solidify a nutrient medium.
• Agar is a good solidifying agent because it will melt only at about the temperature of boiling water and will not resolidify until it is cooled to approximately 43°C.
• Her discovery proved to be a major advance in bacteriologic technique and silenced critics who strongly proclaimed that there was only one species of bacteria that might assume different shapes and forms.
• Richard Petri, one of Koch’s assistants, developed the Petri dish (plate), a container for solid culture media.
• These developments made possible the isolation of pure cultures that contained only one type of bacterium, and directly stimulated progress in all areas of bacteriology.
• Robert Koch introduced the scientific approach to the field of medical microbiology.
• Robert Koch established rules that were necessary to create a cause - and - effect relationship between a microorganism and a disease.
• These rules are now known as Koch’s Postulates.
• Koch’s Postulates state that the microorganism must be found in abundance in all organisms suffering from the disease, but should not be found in healthy organisms.
• The microorganism must be isolated from a diseased organism and grown in pure culture.
• The cultured microorganism should cause disease when introduced into a healthy organism.
• The microorganism must be reisolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent.
• Robert Koch abandoned the universalist requirement of the first postulate altogether when he discovered asymptomatic carriers of cholera and, later, of typhoid fever.
• Asymptomatic or subclinical infection carriers are now known to be a common feature of many infectious diseases, especially viruses such as polio, herpes simplex, HIV, and hepatitis C.
• The second postulate may also be suspended for certain microorganisms or entities that cannot (at the present time) be grown in pure culture, such as prions, suspected as the cause of Creutzfeldt – Jakob disease.
• Viruses also require host cells to grow and reproduce and therefore cannot be grown in pure cultures.
• The third postulate specifies "should", not "must", because as Koch himself proved in regard to both tuberculosis and cholera, not all organisms exposed to an infectious agent will acquire the infection.
• Robert Koch was able to establish the etiology of diseases such as anthrax, cholera and tuberculosis using Koch’s Postulates.
• Vital force provided the basis for the doctrine of spontaneous generation.
• John Needham (1713 - 1781) suggested that spontaneous generation of animalcules resulted from the decay of more complex organisms.
• Needham claimed in a paper published in 1749 that microorganisms arose in his infusions whether he boiled them, covered them, or took any other precautions he could devise.
• Lazzaro Spallanzani (1729 - 1799) improved on Needham’s experimental design by first sealing the glass flasks that contained water and seeds.