Chapter 1 Overview

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Microbiology (Biological Sciences)
All Professors

Microorganisms and Microbiology (Chapter 1) OVERVIEW Lectures focus on important historical events that led to the development of microbiology as a scientific discipline and end with general areas that have developed to the present time. Particularly important is how knowledge of microbiology has almost doubled the average life span in the industrialized world over the last century. OBJECTIVES After completing this chapter you should be able to: • discuss the historical concept of spontaneous generation and the experiments that early scientists performed to disprove this erroneous idea • recognize important historical events that established the discipline of microbiology • understand Koch’s postulates, which are used to establish the causal link between a suspected microorganism and a disease • describe the general method used in isolating pure cultures and the limitations • recognize different areas of the discipline of microbiology • appreciate the role of microbiology in abating diseases and in doubling life expectancy over the last century LECTURE OUTLINE I. The Discovery of Microorganisms Antonie van Leeuwenhoek (1632-1723) constructed microscopes and was the first person to observe and describe bacteria and other microorganisms accurately (footnote at end) II. The Spontaneous Generation Conflict (Consider that only the last two scientists listed below were aware of bacteria). A. The proponents of the concept of spontaneous generation claimed that living organisms could develop from nonliving or decomposing matter B. Francesco Redi (1626-1697) challenged this concept by showing that maggots on decaying meat came from fly eggs deposited on the meat, and not from the meat itself C. John Needham (1713-1781) showed that mutton broth boiled in flasks and then sealed could still develop microorganisms, which supported the theory of spontaneous generation D. Lazzaro Spallanzani (1729-1799) showed that flasks sealed and then boiled had no growth of microorganisms and he proposed that air carried germs to the culture medium. 1 He also commented that external air might be needed to support the growth of animals already in the medium, which was appealing to supporters of spontaneous generation E. Louis Pasteur (1822-1895) heated the necks of flasks, drawing them out into long curves, sterilized the media, and left the flasks open to the air. No growth was observed because dust particles carrying organisms did not reach the medium, instead they were trapped in the neck of the flask. If the necks were broken, dust would settle and the organisms would grow. In this way Pasteur disproved the theory of spontaneous generation III. The Recognition of the Microbial Role in Disease and Culturing of Bacteria A. Robert Koch (1843-1910) established the relationship between Bacillus anthracis and anthrax. His criteria became known as Koch’s Postulates and are still used to establish the link between a particular microorganism and a particular disease: 1. The microorganisms must be present in every case of the disease but absent from healthy individuals (control) 2. The suspected microorganisms must be isolated and grown in 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 diseased host B. The major limitation to Koch’s Postulates is that not all microorganisms grow similarly on laboratory media. Some require nutrients from host organisms, some grow very slowly, and some do not grow on laboratory media at all! C. Fannie & Walter Hess and Richard Petri developed the modern day method used for culturing bacteria and fungi by the use of a
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