Lecture 02: General Microbiology PDF

Department of Mathematics & Natural Sciences MIC101 GENERAL MICROBIOLOGY Lecture 02 Development of Microbiology as a scientific field 1857–1914 1990 to Present First Golden Age...

Department of Mathematics & Natural Sciences MIC101 GENERAL MICROBIOLOGY Lecture 02 Development of Microbiology as a scientific field 1857–1914 1990 to Present First Golden Age Third Golden Age - Fermentation and Pasteurization - Genomics, rDNA technology, Proteomics - The Germ Theory of Disease - Vaccination Second Golden Age - The First Synthetic Drugs - Discovery of antibiotic - Emergence of distinct fields of microbiology 1940–1990 Fermentation Commonly, fermentation means the conversion of carbohydrates to alcohols and carbon dioxide or organic acids. French merchants who would ship beer and wine to long distances would often receive complaints of souring and spoilage of their product. So, they asked Louis Pasteur to identify what was causing this problem and how to fix it. While working on the project, Pasteur identified that microorganisms called yeasts convert the sugars to alcohol (i.e. beer, wine) in absence of air (i.e. oxygen).  And, Pasteur also identified that the souring and spoilage Spoilage caused was occurring due to bacteria not yeast. These unwanted bacteria were growing and converting alcohol into organic by bacteria acids/Vinegar. Acetic Acid Pasteur’s solution to the spoilage problem was to heat the beer and wine just enough to kill most of the bacteria that caused the spoilage. The process, called pasteurization, is now commonly used to reduce spoilage and kill potentially harmful bacteria in milk and other beverages as well as in some alcoholic beverages.  Pasteurization heating a food- usually liquid, to a specific temperature for a definite length of time cooling it immediately process slows microbial growth in food to reduce the number of viable pathogens It was developed by Louis Pasteur Why pasteurization concept derived develop a method that would prevent the spoilage of beverages Pasteur suggested that undesirable types of microbes might be removed by heating – ❖ not enough to ruin the flavor of the products but ❖ enough to control a very high percentage of microbial population. He found that holding the temperature at 62.8o C for half an hour was enough to reach the goal. This process was named pasteurization. The Germ theory: Age of ignorance The early concept For centuries disease was believed to be punishment for ones sins, bad character or poverty etc. It was found to be inconvincible for people that disease was caused by invisible microbe who could travel by air, water to infect plants, animals or humans.  The Germ Theory of Disease Before the time of Pasteur, effective treatments for many diseases were discovered by trial and error, but the causes of the diseases were unknown. The realization that yeasts play a crucial role in fermentation was the first link between the activity of a microorganism and physical and chemical changes in organic materials. This discovery alerted scientists to the possibility that microorganisms might have similar relationships with plants and animals—specifically, that microorganisms might cause disease. This idea was known as the germ theory of disease. Are bacteria responsible for disease? In the 1860s, Joseph Lister, an English surgeon, applied the germ theory to medical procedures. Lister was aware that in the 1840s, the Hungarian physician Ignaz Semmelweis had demonstrated that physicians, who at the time did not disinfect their hands, routinely transmitted infections (puerperal, or childbirth, fever) from one obstetrical patient to another. Lister had also heard of Pasteur’s work connecting microbes to animal diseases. Disinfectants were not used at the time, but Lister knew that phenol (carbolic acid) kills bacteria, so he began treating surgical wounds with a phenol solution. The practice so reduced the incidence of infections and deaths that other surgeons quickly adopted it. His findings provided evidence that microorganisms cause surgical wound infections. Connecting the dots between disease and microbes In 1877, Robert Koch published some early papers on anthrax, a disease of cattle that can also occur in humans. Koch demonstrated that certain bacteria, today known as Bacillus anthracis, were always present in the blood of animals that had the disease and weren’t present in healthy animals. He did a series of tests used to assess the germ theory of disease. He established the link between microbes and infectious diseases and identified causative agents of anthrax and tuberculosis. Microbiology: An Introduction, Textbook by Gerard J. Tortora, 13 th Edition  1. The same pathogen must be present in every case of the disease. 2. The pathogen must be isolated from the Statements 3. diseased host and grown in pure culture. The pathogen from the pure culture must of Koch cause the disease when it’s inoculated into a healthy, susceptible laboratory Postulates animal. 4. The pathogen must be isolated from the inoculated animal and must be shown to be the original organism.  Limitation of Koch’s Postulates Statement 01: The same pathogen must be present in every case of the disease. Limitation: The causative organism might not be present in every stage of the disease. Eg. Vibrio cholerae might not be present at the time of extreme vomiting and diarrhoea because the bacteria release toxin which causes the diarrhoea even in the absence of an organism. Statement 02: The pathogen must be isolated from the diseased host and grown in pure culture. Limitation: Many infectious agents cannot be grown in pure culture, such as prions responsible for Creutzfeldt–Jakob disease. Statement 03: The pathogen from the pure culture must cause the disease when it’s inoculated into a healthy, susceptible laboratory animal. Limitation: Not all hosts exposed to an infectious agent will acquire the infection. Non-infection may be due to such factors as general health and proper immune functioning; acquired immunity from previous exposure or vaccination; or genetic immunity. Development of Bacterial Culture  A microbiological culture means the growth of a defined population of microbes under defined set of parameters. Microbiological culture When microbiological sample collected from an environmental, clinical or pathological origin and is grown in a specific medium under specific temperature, humidity, pressure for specific time, it is called a culture. Culture Media Culture media is the physical and nutritional substance on which microorganism is grown. It contains carbohydrates, proteins, pH to support the growth of microorganisms. Culture media can be of 4 types: ✔ Solid media ✔ Liquid broth ✔ Semisolid media ✔ Biphasic media Diphasic /biphasic medium is called so because of containing medium both solid and liquid states in a single bottle.  Agar, also called agar-agar, gelatin-like product made primarily from the marine red algae Gelidium and Gracilaria (division Rhodophyta). ‘Agar’ is an It is used as solidifying agent for culture media in Petri plates, slants, and deeps important Chemically, it is a complex polysaccharide element of Agar has no nutritional values because microbes don't feed on agar. Agar plates are also inherently sterile until culture media nutrients are added. Generally, it is not metabolized by microbes It liquefies at higher temperature (100°C) It solidifies at lower temperature (~40°C) Good-to-know: Robert Koch played an important role in the development of the use of agar as solid medium. Koch also invented nutrient broth and nutrient agar.  Colony means individual organisms of the same species living closely together, usually for mutual benefit, such as stronger defense or for nutritional requirements. Bacterial colony A bacterial colony is defined as a visible cluster of cells, derived from a single ancestor, they are genetically identical. A colony is often called a colony-forming unit (CFU). Species refers to a group of organisms having same genetic content, morphology, metabolic pattern and are able to reproduce. a. Nutrient Agar a. Blood Agar Useful definitions Inoculation: Inoculation is the introduction of organisms into a defined location such as on a culture media plate. Example, When a sample is added to a sterile medium, it is inoculation of culture. Bacterial Growth: Growth in microbiology is the increase in the number of cells. Example, if we inoculate 2 cells in a culture medium and the cells divide to increase the number of cells, then it is microbial growth. Identification: Identification in microbiology means detecting the taxonomy, genetic makeup, metabolic pattern and virulence factor of an organism. Contamination: Microbiological contamination refers to the non-intended or accidental introduction of infectious material like bacteria, yeast, mould, fungi, virus, prions, protozoa or their toxins and by-products.  Pure culture: When a culture has cells from only one species, it is called a pure culture. Example, If a soil sample is cultured, diluted and processed to isolate every single species, then we have pure cultures of Aspergillus fumigatus, Bacillus subtilis, Pure Culture Bacillus cereus etc. and Mixed Culture Mixed Culture: When a culture has more than one species present in it, it is a mixed culture. Example, A sample from soil has all the virus, bacteria, fungi, algae from the soil. Therefore, it is a mixed culture. Thank you