sumaya yaseen al-dabbagh, msc assistant professor...

General Microbiology | Introduction and History of Microbiology| Dr. Sumaya Yaseen Al-dabbagh Page | 1

Sumaya Yaseen Al-dabbagh, MSc

Assistant Professor, Department of Microbiology

College of Veterinary Medicine, University of Mosul, Mosul, Iraq

https://orcid.org/0000-0001-9370-0775

https://www.researchgate.net/profile/Sumaya_Aldabbagh

General Microbiology | Part I | 3rd

year 2019

Introduction and History of Microbiology

Introduction:

Microbiology: is a branch of biology that studies microorganism and their effect on human

and animals.

Microbes (germ) also called microorganism are minute living thing that individually are too

small to be seen with unaided eye.

Microorganisms includes: (bacteria, fungi, protozoa, microscopic algae and viruses).

Microorganisms are Prokaryotes and Eukaryote.

Microbiologists may have a more applied focus:

Medical microbiology, including immunology

Food and Dairy microbiology

Public Health microbiology (Epidemiology)

Industrial microbiology

Agricultural microbiology

Microbiologists may be interested in various characteristics or activities of

microorganisms

Microbial morphology

Microbial cytology

Microbial physiology

Microbial ecology

Microbial genetics and molecular biology

Microbial taxonomy

History :

In 1546 Fracastorius was one of the first to suggest that animals agents were responsible for

disease.

1665 Robert Hooke reported to the world that life smallest structural unites were little boxes

or cells by using his improved version of compound microscope ( one that uses two sets of

lenses).

Hooke discovery marked the beginning of the cell theory ( all living thing are composed

of cells).

(1673-1680) Antonio Van-Leewenhook , first person to see bacteria in a sample of pus from

his gum, rain water and other liquid ( microscopic animalcules) which were later identified as

infectious agents, by using single lens microscope.

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Spontaneous generation:

Aristotle synthesized the hypothesis which stated that some vital force from inanimate

objects it basic term Spontaneous generation

Needham and many scientists believed that Biogenesis

(some form of life could arise spontaneously from non-living matter).

In 1668, an Italian physician named Francesco Redi came up with a hypothesis to disprove

the idea of spontaneous generation–specifically, the thought [ that maggots could come to

life from meat].

Redi observed that after meat sat out, flies would be attracted to it, and a few days after that

maggots would appear. Redi thought that maggots were from fly eggs too small to be seen.

Redi set up an experiment–with the control and variable groups–to prove his hypothesis

that flies produce maggots.

In the experiment :

1- the control group was a piece of meat in an uncovered jar.

2- The variable group was a piece of meat in a jar covered with gauze; the gauze

allowed air through, but not the flies. After a few days, Redi observed that the control

group had maggots on the meat and the variable group didn’t. He then concluded that

maggots only form when flies come in contact with meat and that spontaneous

generation is not at play.


LOUIS JABLOT

In 1670 Jablot conducted an experiment in which he divided a hay infusion that had

been boiled into two containers: a heated container that was closed to the air and a

heated container that was freely open to the air. Only the open vessel developed

microorganisms. This further helped to disprove abiogenesis.

(1857-1914) Golden age of microbiology:

*Establishment of microbiology as a science.

*Discovery of disease agent.

*Development of vaccines.

* Development of chemotherapy.

Louis Pasteur, in 1864, settled the argument once and for all. Taking the basic idea

of the two scientists from the 1700s and answering critics that said air was necessary for

life, Pasteur developed a special flask, It had a curved neck that allowed air in, but

would trap any microorganisms .

Pasteur showed that his flask was free from microorganisms, even though it was open

to the air for a year, there was no microbial growth. Until Pasteur broke the neck of the

flask. And when microorganisms appeared, he proved to the world that life could only

come from other life. Because of his findings in this and many other experiments

throughout his life, Louis Pasteur is considered one of the greatest Biologists in

history.


*The fermentation process:

Louis Pasteur demonstrated in 1859 that the fermentation process is caused by the

microorganisms, and that this growth is not due to spontaneous generation. Yeasts and

molds, commonly associated with fermentation, Pasteur was an early advocate of the germ

theory of disease.

*Pasteurization:

The process was named after its creator, French chemist and microbiologist Louis Pasteur It is a process which slows microbial growth in food. Pasteurization usually destroy all the non-spore former pathogens.

Pasteur,s work, discoveries included the relationships between microbes and disease, immunity and antimicrobial medicine.

The Germ theory of disease:

The germ theory is one of microbiology significant theories which states the germ that cause

disease e.g. bacteria, fungi and protozoa ,

1546- Fracastorius show that infectious disease can be caused by minute bodies ( germ)

capable of self- replication and transmitted from one infector to another by direct contact.


Edward Jenner (1798): Develop the first Vaccine and used a vaccination procedure to

protect individuals from smallpox

Louis Pasteur (1885) developed other vaccines including those for chicken cholera, anthrax,

and rabies

1834- Agostino Bassi showed that silkworm disease caused by fungi.

Oliver Holmes (1773 - 1843) showed that sepsis could be transmitted by hands of

medical student and may cause disease. Oliver noted that it was safer give birth at home

than in hospital, postulated something present in hospital is causing disease ( nosocomial

disease).

1854- John Snow deduced contaminated Broad Street Pump caused epidemic cholera in

London.

1860-Lister ,was the father of antiseptic surgery ,he used carbolic acid to prevent surgical

wound infection.

1860, Robert Koch was a pioneer in medical microbiology and worked on cholera, anthrax

and tuberculosis. In his research into tuberculosis, Koch finally proved the germ theory, for

which he was awarded a Nobel Prize in 1905. In Koch's postulates, he set out criteria to test

*An organism(pathogen) must be present in all cases of disease.

*pathogen must be isolated and grown in lab in pure culture.

*pathogen from pure culture must cause disease when inoculated into healthy susceptible lab

animal.

these postulates are still used today.

Robert Koch1876- demonstrated that anthrax is caused by Bacillus anthraces.

Pure culture:

A pure culture is defined as a population containing only a single species or strain of

bacteria.

Koch had recognized the difficulties of using broth media for isolation of pure culture and had

looked for solid media alternatives. He evaluated media such as coagulated egg albumen

and aseptically cut slice of potato as used by Schroter, but then moved to a meat extract with

added gelatin.

Development of Culture Media

Why?

To enable the isolation of pure cultures (only one type of organism)

Especially important during Koch’s period


Gelatin not useful as solidifying agent (melts at >28 ºC and some bacteria hydrolyze it

with enzymes)

Fannie Hesse, the wife of one of Koch’s assistants, proposed using agar (a

polysaccharide obtained from various kinds of red seaweed and used in biological

culture media )

Not digested by most bacteria

Melts at 100 ºC and solidify at 42 °C. agar is also clearer than gelatin.

Used today - ~2% in solid media

1887 Richard Petri modified the flat glass plate and produced a new type of culture dish for

media and it named as Petri dish (are covered dishes used to culture microorganisms).

Raymond Sabouraud ( 1890-1910): Develop culture media to study yeast and molds

1876 Tyndall discovered two types of bacteria.

1-Heat sensitive or heat labile forms(vegetative cells)

2-Heat resistant or heat stable forms(endospore).

He found the type of sterilization of liquid either prolonged or intermittent heating to destroy

heat- stable form(can kill all the endospores)

Tyndallization: method of sterilizing liquid by heating it to boiling point on successive days.

Staining:

Bacteria are almost colorless .Staining not only make bacteria more easily seen, but it allows

their morphology (size and shape) to be visualized more easily.

Staining method may be classified as simple, differential and structural.

-Simple stain will react with all microbes .

-Differential stain give varying result depending on the organism being treated .

-Structural stain Specific stain can be used to visualize certain structure (capsule, endospore,

flagella) of bacterial cells.

Development of Vaccines and Antisera:

Edward Jenner in 1796 discovered that cowpox (vaccinia) induced protection against

human smallpox. Called procedure vaccination


Vaccination:

Inoculation of healthy individuals with weakened (or attenuated) forms of microorganisms,

that would otherwise cause disease, to provide protection, or active immunity from disease

upon later exposure.

Pasteur and Roux reported that incubating cultures longer than normal in the lab resulted in

attenuated bacteria that could no longer cause disease.

Working with chicken cholera (caused by Pasteurella multocida), they noticed that animals

injected with attenuated cultures were resistant to the disease.

Pasteur and Chamberland developed other vaccines:

Attenuated anthrax vaccine ,attenuated rabies vaccine

PAUL EHRLICH

In the 1890’s Ehrlich proposed a theory of immunity in which antibodies were responsible

for immunity. In addition, he is known as the father of modern chemotherapy. He

speculated about some “magic bullet” that would selectively find and destroy pathogens but

not harm the host (Selective Toxicity). He also develop a staining procedure to identify

tubercle bacilli

ALEXANDER FLEMING

In 1928 Fleming observed that the growth of the bacterium staphyloccus aureus was

inhibited in the areas surrounding the colony of a mold that had contaminated a Petri plate.

The mold was identified as Penicillium notatum, and its active compound was named

penicillin.

Dimitri Ivanovski (1892): Tobacco mosaic virus could pass through filters used to remove

bacteria.

Selman Waksman (1940): Discovered a number of antibiotic such as Tetracycline and

Streptomycin

Important Early Discoveries :

George W. Beadle and Edward L. Tatum (ca. 1941)

studied the relationship between genes and enzymes using the bread mold,

Neurospora

One gene, one polypeptide hypothesis

Salvadore Luria and Max Delbruck (ca. 1943)

Demonstrated spontaneous gene mutations in bacteria


WATSON and CRICK, FRANKLIN, and WILKINS

In 1953 Watson and Crick determined the structure of DNA. They used their research,

together with the research of Franklin and Wilkins to determine the structure of the DNA

molecule.

Microscope: Various types of microscopes are available for use in the

microbiology laboratory.

Types of Microscopes:

1-The Bright-Field Microscope

2-The Dark -field Microscope

3-The Phase-Contrast Microscope

4-The Fluorescence Microscope

5-The Transmission Electron Microscope

6-The Scanning Electron Microscope

Bright-Field microscope: The common light microscope used in the laboratory

is called a compound microscope because it contains two types of lenses that

function to magnify an object. The lens closest to the eye is called the ocular,

while the lens closest to the object is called the objective. Most microscopes

have on their base an apparatus called a condenser, which condenses light rays

to a strong beam. A diaphragm located on the condenser controls the amount

of light coming through it. Both coarse and fine adjustments are found on the

light microscope (Figure).


total magnification

• product of multiplying the magnifications of the ocular lens and the

objective lens

• Microscope Resolution

ability of a lens to separate or distinguish small objects that are close

together

wavelength of light used is major factor in resolution

shorter wavelength greater resolution

Dark‐field microscope: which is used to observe live spirochetes, such as

those that cause syphilis. This microscope contains a special condenser that

scatters light and causes it to reflect off the specimen at an angle. A light object

is seen on a dark background.


Phase‐contrast microscope: This microscope also contains special condensers

that throw light “out of phase” and cause it to pass through the object at

different speeds. Live, unstained organisms are seen clearly with this

microscope, and internal cell parts such as mitochondria, lysosomes, and

the Golgi body can be seen with this instrument.

Fluorescent microscope: uses ultraviolet light as its light source. When ultraviolet light hits an object, it excites the electrons of the object, and they

give off light in various shades of color. Since ultraviolet light is used, the resolution of the object increases. A laboratory technique called the fluorescent‐

antibody technique employs fluorescent dyes and antibodies to help identify unknown bacteria

Electron microscopy: The energy source used in the electron

microscope is a beam of electrons. Since the beam has an exceptionally short

wavelength, it strikes most objects in its path and increases the resolution of the

microscope significantly. Viruses and some large molecules can be seen

with this instrument.

The more traditional form of electron microscope is transmission electron

microscope (TEM). To use this instrument, one places ultrathin slices of

microorganisms or viruses on a wire grid and then stains them with gold or

palladium before viewing. The beam is focused on a small area of the specimen

by an electromagnetic condenser.

EM use electromagnetic lenses to control illumination, focus and magnification.

Image produce by electron microscope are always black and white,

Scanning electron microscope (SEM) is the more contemporary form

electron microscope. Although this microscope gives lower magnifications than

the TEM, the SEM permits three-dimensional views of microorganisms and

other objects. Whole objects are used, and gold or palladium staining is

employed.

sumaya yaseen al-dabbagh, msc assistant professor...

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