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The Importance of Microorganisms

Chapter 1 The History and Scope of Microbiology

 Most populous group of organisms and are

found everywhere on the planet elements

 Play a major role in recycling essential  Source of nutrients and some carry out


 Benefit society by their production of food,

beverages, antibiotics and vitamins



Whatis microbiology?
 Study of organisms too small to be clearly

Members of the microbial world
 procaryotic cells lack a true membrane-delimited

seen by the unaided eye (i.e., microorganisms)
 These organisms are relatively simple in their

 eucaryotic cells have a membrane-enclosed

construction and lack highly differentiated cells and distinct tissues

nucleus, are morecomplex morphologically and are usually larger than procaryotic cells





Classification schemes
 Five kingdom scheme includes Monera,

Protista, Fungi, Animalia and Plantae with microbes placed in the first three kingdoms
 Three domain alternative, based on a

comparison of ribosomal RNA, divides microorganisms into Bacteria (true bacteria), Archaea andEucarya (eucaryotes)
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Domain Bacteria – all procaryotic
 Most are single-celled  Most have peptidoglycan in cell wall  Can survive broad range of environments  Most are non-pathogenic and play major role in

Domain Archaea – all procaryotic
 Procaryotic  Distinguished from bacteria by unique

ribosomal rna sequences
 Lack peptidoglycan in cell wall  Many found in extremeenvironments

nutrient recycling
 Cyanobacteria produce oxygen as a result of

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 No pathogenic species known



Domain Eucarya – all eucaryotic
 Animals, plants and eucaryotic

 Acellular

 Microorganisms include protists

 Smallest of all microbes  Cause a range of diseases including

(unicellular algae, protozoa,slime molds and water molds) and fungi
 Most are larger than procaryotic cells
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some cancers

Discovery of Microorganisms
 Antony van

Leeuwenhoek (1632-1723)
 first person to

observe and describe microorganisms accurately





The Conflict over Spontaneous Generation
 Spontaneous generation  Living organisms can develop from nonliving

Butcould spontaneous generation be true for microorganisms?
 John Needham (1713-1781)  His experiment:
Mutton broth in flasks  boiled sealed

or decomposing matter
 Francesco redi (1626-1697)  Disproved spontaneous generation for large

 Results: broth became cloudy and contained

 Lazzaro Spallanzani (1729-1799)
 His experiment:

animals  Showed that maggots ondecaying meat came from fly eggs
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Broth in flasks sealed  boiled

 Results: no growth of microorganisms

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Louis Pasteur (1822-1895)
 His experiments  Placed nutrient solution in flasks  Created flasks with long, curved necks  Boiled the solutions  Left flasks exposed to air  Results:no growth of microorganisms

Louis Pasteur (1822-1895)





Final blow to theory of spontaneous generation
 John Tyndall (1820-1893)
 Demonstrated that dust carries

The Role of Microorganisms in Disease
 Was not immediately obvious  Establishing connection depended on

 Showed that if dust was absent, nutrient

broths remainedsterile, even if directly exposed to air
 Also provided evidence for the existence of

development of techniques for studying microbes
 Once established, led to study of host

exceptionally heat-resistant forms of bacteria
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defenses - immunology

The golden age of microbiology (1857-1914)
 Many disease producing organisms

 Microbial metabolism studies undertaken ...
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