Presentation on theme: "The History of Microbiology (Key events that advanced our understanding of microorganisms)"— Presentation transcript:
The History of Microbiology (Key events that advanced our understanding of microorganisms)
Microbes have been around for a long time Thought to be the first living entities on earth::photosynthetic bacteria were responsible for generating oxygen for the support of life Cyanobacteria—photosynthetic microorganisms were the first O 2 -evolving organisms on Earth and may have been responsible for oxygenating the atmosphere
Evidence for the production of beer, wine and bread Evidence for food preservation with salt and drying. (Ships undertaking long passages to the Americas used these practices) Francis Bacon (1561-1626) Had a theory that freezing should retard the spoilage of chickens—died testing the theory People were aware of an invisible force that affected food and involved microbes.
People were aware that an invisible force caused sickness and death 1300’s height of the first plague: implementation of quarantenaria by the Italians
More evidence for human awareness of disease causing microorganisms Girolamo Fracastoro 1546 (200 years after the first plague) Philosophical treatise “De Contagione et Contagiosis Morbis” --some diseases are caused by the transmission of germs 3 possible modes for the transmission of contagion 1. Direct contact 2. Transmission via inanimate objects 3. Transmission from a distance --contagion or disease processes and the putrefaction of food are analogous.
Germs have a form::invention of the microscope Johannes and Zacharias Jansen (spectacle makers) –1590—two convex lenses in sequence magnifies and image Galileo (Italian astronomer) –1624 improved precursor to the light microscope Anton van Leeuwenhoek (cloth draper) –1674 designed own microscopes, first to describe bacteria, yeasts and protozoa— ”wee animalcules” Ernst Abbe (German physicist) --1882 developed better lenses for microscopes, developed the oil immersion lens Paul Ehrlich –1881 staining with methylene blue Christian Gram –1884 differential staining with methylene blue and safronin.
Leuwenhoek’s microscope and drawings of some of his “wee animalcules”
Hooke’s microscope (progenitor to the modern day microscope) and his observations Hooke was a contemporary of Leuwenhoek and invented the microscope around the same time
The controversy regarding “spontaneous generation” in food spoilage The belief that living forms sprang from non-living matter proponents: putrefaction is a result of chemical events opponents: putrefaction is caused by “germs” Francesco Redi – 1668 Showed that flies were responsible for maggots found on the surface of rotting meat. John Needham –1748 organic infusions spoiled in stoppered bottles Abbe Lazzaro Spellanzani—1765 boiled the organic infusions, infusions remained “barren” for a long time unless the seal was broken Louis Pasteur –1861—trained as a scientist and used “scientific method” to address the issue.
Scientific Method 1.STATE THE PROBLEM 2.FORM A HYPOTHESIS AFTER GATHERING ALL INFORMATION ON THE TOPIC 3.DEVISE EXPERIMENTS TO TEST THE VALIDITY OF THE HYPOTHESIS 4.OBSERVE RESULTS OF THE EXPERIMENT 5.INTERPRET THE DATA 6.DRAW CONCLUSIONS 7.ALWAYS CAREFULLY DOCUMENT DESIGN AND RESULTS OF THE EXPERIMENT!!!
Pasteur’s Scientific Method 1.STATE THE PROBLEM A. Food allowed to stand for some time spoiled B. Wine and beer do not always come out the way it should
Pasteur’s Scientific Method 2. FORM A HYPOTHESIS AFTER GATHERING ALL INFORMATION ON THE TOPIC Observed that structures in the air that resembled micro organisms found in putrefied materials Passed air through cotton/ released trapped materials in liquid and observed microorganisms via microscopy HYPOTHESIS: Microorganisms found in putrefying food originate from microbes in the air—foods protected from the airbourne microbes should not putrefy.
1861—Louis Pasteur refutes the theory of spontaneous generation (good example of a controlled experiment)
Pasteur’s Scientific Method 4.DRAW CONCLUSIONS The souring of milk, beer and wine is due to microorganisms Microorganisms in these products can be killed by heating Some advancements from these studies and conclusions: 1867—pasteurization –heating food to 55-60 o C for a short time
Pasteurization is commonly used to remove pathogenic organisms from food products Historically: Used to kill organisms causing brucellosis, typhoid fever and tuberculosis in dairy products Today: Used to kill Salmonella spp and Escherichia coli O157:H7 Doesn’t kill all of the organisms Process: Passing raw milk through a heat exchanger such that small volumes of milk are briefly heated to 71 o C for 15 seconds, the milk is rapidly cooled and maintained at the low temperature
The effect of temperature on the viability of a typical mesophillic bacterium Decimal Reduction Time = the length of time a bacterial population must be exposed at a given temperature to kill 90% of the population
Caveats to using lower temperatures for the “eradication” of microorganisms The thermal death time depends on the size of the initial bacterial population The high sugar, protein and fat content of some products decrease heat penetration and increase the resistance of the organisms in these products to heat Endospores are moderately heat resistant—contain compounds that are resistant to heat, have little water activity, are metabolically inert and are surrounded by a thick keratin coat.
John Tyndall and Ferdinand Cohn—1877 Discovery of heat resistant forms of bacteria John Tyndall: bacteria have a heat labile or heat sensitive form and a heat resistant form Cohn –the heat resistant forms of bacteria form endospores endospores become vegetative after one heating process. Repeated heating and cooling eliminates viable organisms— Tyndallization Charles Chamberland—1881 designed an autoclave –large pressure cooker,
Endospores Accumulation of Calcium, small acid soluble spore proteins (SASPs) and Dipicolinic acid that forms a gel like structure which excludes water Contraction of the cortex st.V results in a shrunken protoplast
Endospores: Note how these structures are resistant to heat, irradiation and chemicals compared to vegetative cells and note how they are low in water content and metabolically inert *
The Autoclave— an effective means for killing heat resistant bacteria and endospores The chamber is heated under low atmospheric pressure conditions such that it is possible to increase the chamber temperature to 121 o C.
High Temperatures (121 o C) for at least 15 minutes—longer for larger volumes that take longer to reach this temperature Endospores require approximately 5 minutes for a decimal reduction The autoclave (cont’d)