Prescott's Microbiology Chapter 1 - University Of Jordan

Prescott's MicrobiologyChapter 1The Discovery of MicroorganismsThis chapter introduces the field of microbiology and discusses theimportance of microorganisms not only as causative agents ofdisease but also as important contributors to food production,antibiotic manufacture, vaccine development, and environmentalmanagement. It presents a brief history of the science ofmicrobiology, an overview of the microbial world, and a discussionof the scope and relevance of microbiology in today's society.CHAPTER OBJECTIVESAfter reading this chapter you should be able to:1. Define the science of microbiology and describe some of the generalmethods used in the study of microorganisms2. Discuss the historical concept of spontaneous generation and theexperiments that were performed to disprove this erroneous idea3. Discuss Koch's postulates, which are used to establish the causal linkbetween a suspected microorganism and a disease4. Describe some of the various nonpathological activities of microorganisms5. Describe prokaryotic and eukaryotic morphology, the two types of cellularanatomy, and also the distribution of microorganisms among the variouskingdoms or domains in which living organisms are categorized6. Discuss the importance of the field of microbiology to other areas of biologyand to general human welfareMicrobiology: Is the field of study concerned with microorganisms(microscopic organisms) Too small to be clearly seen by the unaided eye(micrometer) that for the most part they were not observedprior to the advent of the microscope.

Types of microorganisms: Viruses, bacteria, protozoa, algae, and fungi Some algae and fungi are large enough to be visible, but areincluded in the field of microbiology because they havesimilar properties and because similar techniques areemployed to study them (isolation, sterilization, culture inartificial media)Early discovery of microorganisms Antony van Leeuwenhoekmicroscopes and was the first person to observe anddescribe microorganisms accuratelyThe Spontaneous Generation ConflictA. The spontaneous generation claimed that living organismscould develop from nonliving or decomposing matterB. Francesco Redi (1626-1697) challenged this concept byshowing that maggots on decaying meat came from fly eggsdeposited on the meat, and not from the meat itself

C. John Needham (1713-1781) showed that mutton broth boiledin flasks and then sealed could still develop microorganisms, whichsupported the theory of spontaneous generationD. Lazzaro Spallanzani (1729-1799) showed that flasks sealedand then boiled had no growth of microorganisms, and heproposed that air carried germs to the culture medium; he alsocommented that external air might be needed to support thegrowth of animals already in the medium; the latter concept wasappealing to supporters of spontaneous generationE. Louis Pasteur (1822-1895)o Louis Pasteur developed vaccines including those forchicken cholera, anthrax, and rabieso He trapped airborne organisms in cotton; he also heated thenecks of flasks, drawing them out into long curves, sterilizedthe media, and left the flasks open to the air; no growth wasobserved because dust particles carrying organisms did notreach the medium, instead they were trapped in the neck ofthe flask; if the necks were broken, dust would settle and the

organisms would grow; in this way Pasteur disproved thetheory of spontaneous generationThe swan neck flask experiment. Pasteur filled a flask with medium,heated it to kill all life, and then drew out the neck of the flask into a longS shape. This prevented microorganisms in the air from easily enteringthe flask, yet allowed some air interchange. If the swan neck was broken,microbes readily entered the flask and grew.Pasteur's ExperimentThe steps of Pasteur's experiment are outlined below:1. First, Pasteur prepared a nutrient broth similar to the broth one would use in soup.2. Next, he placed equal amounts of the broth into two long-necked flasks. He left oneflask with a straight neck. The other he bent to form an "S" shape.

Images courtesy William Harris3. Then he boiled the broth in each flask to kill any living matter in the liquid. Thesterile broths were then left to sit, at room temperature and exposed to the air, in theiropen-mouthed flasks.4. After several weeks, Pasteur observed that the broth in the straight-neck flask wasdiscolored and cloudy, while the broth in the curved-neck flask had not changed.5. He concluded that germs in the air were able to fall unobstructed down the straightnecked flask and contaminate the broth. The other flask, however, trapped germs inits curved neck, preventing them from reaching the broth, which never changed coloror became cloudy.

6. If spontaneous generation had been a real phenomenon, Pasteur argued, the broth inthe curved-neck flask would have eventually become reinfected because the germswould have spontaneously generated. But the curved-neck flask never becameinfected, indicating that the germs could only come from other germs.Pasteur's experiment has all of the hallmarks of modern scientific inquiry. It begins with ahypothesis and it tests that hypothesis using a carefully controlled experiment. This sameprocess -- based on the same logical sequence of steps -- has been employed by scientists fornearly 150 years. Over time, these steps have evolved into an idealized methodology that wenow know as the scientific method.F. John Tyndall (1820-1893) demonstrated that dust did carrymicrobes and that if dust was absent, the broth remained sterileeven if it was directly exposed to air;Tyndall also provided evidence for the existence of heat-resistantforms of bacteriaIII. The Recognition of the Microbial Role in DiseaseJoseph Lister (1872-1912) developed a system of surgerydesigned to prevent microorganisms from entering woundsRobert Koch (1843-1910) established the relationshipbetween Bacillus anthracis and anthrax; his criteria became knownas Koch's Postulates and are still used to establish the linkbetween a particular microorganism and a particular disease:

1. The microorganisms must be present in every case of the disease butabsent from healthy individuals2. The suspected microorganisms must be isolated and grown in pure culture3. The same disease must result when the isolated microorganism isinoculated into a healthy host4. The same microorganism must be isolated again from the diseased hostIV. The Discovery of Microbial Effects on Organic andInorganic MatterLouis Pasteur demonstrated that

Alcoholic fermentations were the result of microbialactivity, that some organisms could decrease alcohol yieldand sour the product Some fermentations were aerobic and some anaerobic Developed the process of pasteurization to preserve wineduring storage

Prescott's Microbiology Chapter 1 The Discovery of Microorganisms This chapter introduces the field of microbiology and discusses the importance of microorganisms not only as causative agents of disease but also as important contributors to food production, antibiotic manufa