Main Themes of Microbiology

Chapter 1

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2

Scientific method

• Hypothesis - a conditional explanation that can be verified or falsified (is testable).

Experimental Design

• Independent variable

• Dependent variable

• Controlled conditions

Scientific Theories and Laws Are the Most Important Results of Science

• Scientific theory

• Widely tested

• Supported by extensive evidence

• Accepted by most scientists in a particular area

• Scientific law, law of nature has no known exceptions.

Microbiology Accomplishments

• Cell Theory (Robert Hooke, Antonie van Leeuwenhoek, Theodor Schwann, Matthias Jakob Schleiden)

• Abiogenesis debate (Francesco Redi, Lazzaro Spallanzani, Louis Pasteur, John Tyndall, Ferdinand Cohn)

• Germ Theory of Disease/Sanitation (Louis Pasteur, Robert Koch, Joseph Lister)

• Vaccination (Edward Jenner, Louis Pasteur, Maurice Hillerman)

• Antibiotics ( Paul Ehrlich, Alexander Fleming, Gerhard Domagk, Howard Florey and Ernst Chain)

The Discovery of Microbes

• People have long been aware of the effects of microbial growth

• Spoilage, disease, decomposition

• Microbes are too small to be seen even with hand lenses

• Microscopes changed that

Robert Hooke

• 1665

• English naturalistand architect

• May have been the first to see microorganisms

• Coined the word “cell” to describe what he saw while viewing tree barkfrom a cork oak.

Antonie van Leeuwenhoek

• 1674

• Dutch fabric merchant

• First person to accurately describe living microbes

• Used a simple microscope

• Made and reported many detailed observations

LensSpecimen

holder

Focusscrew

Handle

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Cell Theory

• Proposed by Theodor Schwann and Matthias Jakob Schleiden in 1839

• States that:

All living things or organisms are made of cells and their products.

New cells are created by old cells dividing into two.

Cells are the basic building units of life.

The Spontaneous Generation Debate

• Biogenesis: living things originate from other living things

• Spontaneous generation (abiogenesis): life rapidly appears from non-living things.

Origins of Abiogenesis

• No distinction between living and non-living in the early human mind

• Aristotle: 400 BC – Favored spontaneous generation

• Concluded that aphids, fleas, flies, and even mice could spontaneously form from other organic materials

Disproval of Abiogenesis

• Francesco Redi (1668) Disproved spontaneous generation of maggots

• Lazzaro Spallanzani (1768) Proved that microorganisms can be killed by boiling

• Nicolas Appert, the father of canning.

Louis Pasteur

• Used swan-necked flasks to disprove abiogenesis conclusively (1859)

• The discovery led to invention of pasteurization and autoclave.

Pasteur’s Experiment

Microbesbeingdestroyed

Vigorous heatis applied.

Broth free oflive cells (sterile)

Neck intact; airbornemicrobes are

trapped at base,and broth is sterile.

Neck on secondsterile flaskis broken;

growth occurs.

Discovery of Endospores

• John Tyndall (1876)

• Described heat-resistant microbes from hay infusions

• Used discontinuous heating used to sterilize (tyndalization)

• Ferdinand Cohn (1876)

• Discovered and described endospores in some soil bacteria (Bacillus)

Germ Theory of Disease

• Epidemics caused by miasma, a noxious form of "bad air"

• John Snow (1849) tied cholera outbreak to a contaminated water source

Germ Theory of Disease

• Louis Pasteur – showed that silkworm disease was caused by a protozoan parasite

• Robert Koch – proved that a specific bacteria caused a specific disease - linked Bacillus anthracis to anthrax in cattle; described several postulates for proving the etiological (causative) agent of disease (1884)

Koch’s Postulates

• A specific microorganism causes an infectious disease

• Isolate microorganism

• Infection with pure microbe results in disease

• Re-isolate microorganism from infected individual

Development of Aseptic Techniques

• Ignaz Semmelweiss (1847)– proposed that surgeons wash their hands with chlorinated lime solution to prevent transmission of childbirth fever

• Joseph Lister (1870s) – introduced aseptic techniques; used carbolic acid (phenol) to clean hands, wounds and operating rooms to reduce the number of post-operative infections.

Vaccination

• The earliest documented examples of vaccination from India and China (17th century), to protect against the small pox

• The Anatolian Ottoman Turks used inoculation of small pox scab matter to protect against the disease.

• Edward Jenner (1796), the “father” of vaccination

• Luis Pasteur developed killed vaccines to protect against anthrax and rabies

• Maurice Ralph Hilleman developed 36 vaccines.

Recent Developments in Technology

• Restriction Enzymes

• Polymerase Chain Reaction (PCR)

• Biofilms

• Small RNAs

Microbial Classification

• Taxonomy is the science of classifying living things. Taxa (singular: taxon) categories that show the degree of similarity between organisms

• Systematics or Phylogeny is the study of the evolutionary history of organisms.

• Nomenclature naming living organisms.

• Identification studying of traits of a specific organism in order to put it into a specific group

The Five Kingdom

Model

EU

KA

RY

OT

ES

PR

OK

AR

YO

TE

S

Seed plants

First eukaryoticcells appeared 2 billion years ago.

(Protista)PROTISTS

First multicellularorganisms appeared 0.6 billion years ago.

Sponges

Flatworms

Nematodes

Echinoderms

ChordatesArthropods

Annelids

Mollusks

ANIMALS(Animalia)

Molds

Clubfungi

Yeasts

(Myceteae)FUNGI

Ciliates

Amoebas

Flagellates

Apicomplexans

Early eukaryotes

Bacteria

First cells appeared3–4 billion years ago.

Earliest cell2 cell types5 kingdoms

Archaea

MONERA

Dinoflagellates

Diatoms

Brownalgae

Redalgae

Green algae

Slimemolds

(Plantae)PLANTS

Ferns

Angiosperms

Gymnosperms

Mosses

Robert Whittaker (1959)

Taxonomy

• Kingdom Kings

• Phylum Play

• Class Chess

• Order On

• Family Fine

• Genus Green

• Species Satin

Kingdom: Animalia

Phylum: Chordata

Class: Mammalia

Order: Primates

Family: Hominoidea

Genus: Homo

Species: sapiens

Kingdom: Protistaincludes protozoa and algae

Phylum: Ciliophoraonly protozoawith cilia

Class: HymenostomeaSingle cells withregular rows ofcilia; rapid swimmers

Order: HymenostomatidaElongate oval cells withcilia in the oral cavity

Family: ParameciidaeCells rotate while swimmingand have oral grooves.

Genus: ParameciumPointed, cigar-shaped cells withmacronuclei and micronuclei

Species: Caudatum Cells cylindrical, long and pointed at one end

()

Domain: Eukarya (All eukaryotic organisms)

Domain: Eukarya (All eukaryotic organisms)

Lemur

Sea starSea squirt

New Views of Phylogeny

• Based on 16S RNA sequence

Domain Bacteria Domain Archaea Domain Eukarya

Cyanobacteria

ChlamydiasSpirochetes

Gram-positivebacteria

Endosporeproducers

Gram-negativebacteria

Methaneproducers

Prokaryotesthat live inextreme salt

Prokaryotesthat live inextreme heat

Eukaryotes

Ancestral Cell Line (first living cells)

Nomenclature

• Designed by Carilus Linnaeus

• Every organism has a two-name (binomial) designation – Genus species

• Note italics and the capitalization!

Conclusions:

• The scientific method is a process of observation, hypothesis generation, data collection, analysis of results, and dissemination of findings. Proper experimental design, repetition of measurements or experiments is critical if one is to determine the validity of findings.

• Scientific theories are thoroughly tested before being accepted. They can be modified after being accepted.

• The major accomplishments of microbiology are: Cell Theory, disproval of abiogenesis, germ theory of disease and invention of sanitation, discovery of vaccination and antibiotics.

Conclusions:

• The five kingdom model of classification of the living world is based on structural similarities, cellular organization, and nutritional type, and it includes Monera (Bacteria and Archaebacteria), Protists, Plants, Fungi, and Animals.

• The taxonomic categories from top to bottom are: kingdom, philum, class, order, family, genus and species.

• The Woese-Fox phylogenetic system is based on the similarity of 16S RNA sequence, and includes domains Bacteria, Archea and Eucarya