Chapter 1: The Microbial World and You

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14 Δεκ 2012 (πριν από 4 χρόνια και 4 μήνες)

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Chapter 1:
A Brief History of
Microbiology

Microbiology:


The study of microorganisms.

Microorganisms
: Small living organisms that
generally can not be seen with the naked eye.

Include:


Bacteria


Fungi (yeasts and molds)


Protozoa


Algae


Multicellular parasites

Also include
nonliving

infectious agents:


Viruses



Prions


Microbes are Essential for Life on
Earth:
Have many important and beneficial
biological functions:



Photosynthesis:
Algae and some bacteria
capture energy from sunlight and convert it to
food, forming the basis of the
food chain
.



Decomposers:
Many microbes break down
dead and decaying matter and
recycle nutrients

that can be used by other organisms.



Nitrogen Fixation
: Some bacteria can take
nitrogen from air and incorporate it into soil.


I
mportant and beneficial biological functions of
Microbes:




Digestion:
Animals have microorganisms in their
digestive tract, that are essential for digestion, vitamin
synthesis, and overall health.



Cellulose digestion (termites, cows, rabbits, etc.)



Vitamin K and B synthesis in humans



Prevent the overgrowth of pathogenic bacteria and yeast



Medicine:

Many
antibiotics

and other drugs are
naturally synthesized by microbes.



Penicillin is made by a mold

Penicillin is Produced by a Mold


I
mportant and beneficial biological
functions of Microbes:



Food Industry:

Many important foods and
beverages are made with microbes:



Alcoholic beverages (Wine, beer, rum, whiskey)



Bread



Vinegar



Soy sauce



Cheese



Pickles, olives, sauerkraut



Yogurt



Buttermilk



Sour cream



Coffee



Chocolate



Hams, sausages


I
mportant and beneficial biological
functions of Microbes:



Genetic Engineering:

Recent advances in
gene splicing allow us to design
recombinant
microbes that produce important products:



Human growth hormone (Dwarfism)



Insulin (Diabetes)



Blood clotting factor (Hemophilia)



Recombinant vaccines


Hepatitis A and B vaccines



Human hemoglobin (Emergency blood substitute)



Taxol (Breast and ovarian cancer)



Erythropoietin (Anemia)



Monoclonal antibodies (Disease diagnosis and
prevention).


I
mportant and beneficial biological
functions of Microbes:



Medical Research:

Microbes are well suited
for biological and medical research for several
reasons:



Relatively simple and small structures, easy to
study.



Genetic material is easily manipulated.



Can grow a large number of cells very quickly and
at low cost.


Short generation times make them very useful to
study genetic changes.


Microbes and Disease:

Most microbes are
either beneficial or harmless to humans.



Less than 1% of microbes cause disease.



In 1962, the surgeon general of the United
States stated: “The war against infectious
diseases has been won”.


Today it is clear that this was overly optimistic:



Emerging diseases
: New diseases like AIDS,
hantavirus, Ebola fever, Lyme disease, Hepatitis C,
and others that did not exist a few years ago.



Antibiotic and Drug Resistance:
Many old
diseases are becoming resistant to traditional
therapies: Tuberculosis, gonorrhea, malaria, etc.



Today infectious diseases cause 50% of the
52 million worldwide deaths per year.








Infectious Diseases Causing Most
Deaths Worldwide in 2000

Disease


Cause


Deaths/year

Acute Respiratory
*
Bacterial or viral

4,400,000

Diarrheal diseases

Bacterial or viral

3,200,000

Tuberculosis

Bacterial


3,100,000

Malaria


Protozoan


3,100,000

Hepatitis B


Viral



2,000,000

Measles


Viral



1,500,000

AIDS



Viral



1,000,000

Neonatal Tetanus

Bacterial


600,000

*
: Pneumonia, bronchitis, influenza, etc.



Neonatal tetanus kills over 600,000 infants every year.

Source: Tropical Medicine and Parasitology, 1997.







Microbes and Disease in Human
History


Bubonic Plague (Black death)
: Several
devastating epidemics throughout history.


High mortality: Up to 80% of those infected die.


1347
-
1351: Over 75 million died in Europe,
Asia, and Africa.


Over 25% of population of Europe died.


Cause was unknown for over 500 years, leading
to superstition, persecution, and hysteria.


Bacterial

disease transmitted by rat fleas.


Rare today but still occurs:


10
-
15 cases/year in U.S.


Last epidemic occurred in India in 1994.






Left: Swollen lymph nodes in bubonic plague infection.

Right: Infected flea bite with eschar and carbuncle.

Source: Tropical Medicine and Parasitology, 1997.

Worldwide Distribution of Plague

++: Frequent transmission

+/
-
: Infrequent transmission.

Source: Tropical Medicine and Parasitology, 1997.








Smallpox:

One of deadliest human
infectious diseases throughout history.


Caused by
smallpox virus
.


First known case in 1175 B.C.: Egyptian
pharaoh Ramses V died from smallpox.


Several hundred million deaths through history.


Up to 90% of Native American population was
killed

by smallpox and other diseases (measles
and plague) introduced during European
conquests.


Native population of Central and South America dropped
from 130 million to about 1.6 million over several decades.


Smallpox was used as a

biological weapon

by British
colonists in North America.


600,000 deaths/year in Europe from 1500
-
1700.

Smallpox infection in a small child.

Disease was eradicated worldwide by immunization in 1977.

Source: Microbiology Perspectives, 1999.









Smallpox (Continued)



75% of survivors were severely scarred and/or
blinded.


An effective vaccine was developed in 1870s by
Edward Jenner, using a related virus (cowpox).


Smallpox was the first and only viral disease to
be completely
eradicated

(1977).


Worldwide immunization campaign in 1960s.


Only infects humans.










Tuberculosis (TB):

Caused by a
bacterium

that
mainly infects lungs but may spread to other parts of
body.


Leading killer of world’s infectious diseases:


3 million die worldwide every year.


Over 1 million killed in U.S. between 1930
-
49.


One out of three people infected worldwide.


In U.S. 10 million people are presently infected, but only 5% will
develop active disease.


Most healthy individuals can contain infection.


Treatment
: Antibiotics for up to one year or longer.


After introduction of antibiotics, TB declined from 1950s to 80s, and
then started to increase again.


Low patient compliance

with treatment has caused
antibiotic
resistant TB
.


AIDS epidemic has caused an increase in cases.



Tuberculosis is leading killer among infectious diseases

worldwide. Patient with lymph node necrosis.

Photo by Dr. I. Small








Childbirth Fever
: Common

nosocomial

(hospital acquired) infection
.


Bacterial

infection of the uterus as a result of
childbirth or abortion.


Transmitted by hands and instruments of
physicians and midwives.


Extremely common before the 1900s.


About 1 in 17 women who gave birth would become
infected (fever, chills, delirium, and death).


Cause was unknown.


Austrian doctor Semmelweiss showed that washing
hands and instruments with a disinfectant solution
greatly reduced cases.


Today common in women who have illegal
abortions, especially in third world countries.










AIDS
: Acquired Immune Deficiency Syndrome
.


First cases reported in 1981 at UCLA.


Cause:
Human

Immunodeficiency

Virus

(
HIV
)


Transmitted by sexual contact, blood transfusions, mother
-
to
-
child, and infected needles.


Destroys an individual’s immune system, making them
susceptible to many infectious diseases and cancer.


Number of cases has grown rapidly during the last two
decades. As of 2004:


Over 1’000,000 individuals with AIDS in the U.S.


Over 500,000 US AIDS patients have died


Over 40 million deaths worldwide.



African AIDS patient with slim disease

Source: Tropical Medicine and Parasitology, 1997

Endemic Kaposi’s Sarcoma, nodular form in an AIDS patient.

Source: AIDS, 1997.

Extensive symmetric tumor lesions of Kaposis’s sarcoma in an
AIDS patient.

Source: AIDS, 1997

Oral candidiasis (yeast infection) in an AIDS patient

Source: Atlas of Clinical Oral Pathology, 1999







History of Microbiology

Early Studies

Before 17th century, study of microbiology was
hampered by the lack of appropriate tools to
observe microbes.


Robert Hooke
: In 1665 built a compound light
microscope and used it to observe thin slices of
cork. Coined the word
cell
.


Anton van Leeuwenhoeck:

In 1673 was the first
person to observe live microorganisms which he
called “
animalcules
” (bacteria, protozoa), using
single
-
lens microscopes that he designed.









History of Microbiology

Spontaneous Generation vs Biogenesis


Before 1860s many scientists believed in
Spontaneous generation
, i.e.: That living
organisms could arise spontaneously from
nonliving matter:



Mice come from rags in a basket.



Maggots come from rotting meat.



Ants come from honey.



Microbes come from spoiled broth.







History of Microbiology

Spontaneous Generation vs Biogenesis


Theory of Biogenesis:

Belief that living cells can
only arise from other living cells.


Francesco Redi
: In 1668 proved that maggots do
not arise spontaneously from decaying meat.


Lazaro Spallanzani:

In 1765 found that nutrient
broth that had been heated in a sealed flask would
not become contaminated with microbes.



Some proponents of spontaneous generation argued that
boiling had destroyed the “life force” of air in flask.



Others argued that microbes were different from other life
forms.









History of Microbiology

Spontaneous Generation vs Biogenesis

Debate was finally settled by Pasteur.


Louis Pasteur
: In 1861 finally disproved
spontaneous generation when he demonstrated
that microorganisms in the environment were
responsible for microbial growth in nutrient broth.


Designed
swan neck flasks

that allowed air in, but
trapped microbes in neck.


Developed
aseptic technique
: Practices that prevent
contamination by unwanted microorganisms.







History of Microbiology

Golden Age: 1857
-
1914

Rapid advances led to the development of
microbiology as a science.

Pasteur’s Contributions to Microbiology:


Fermentation
: Pasteur found that yeasts were
responsible for converting sugar into alcohol in
the absence of air.


Souring and spoilage were caused by bacterial
contamination of beverages.







History of Microbiology

Golden Age: 1857
-
1914

Pasteur’s Contributions:


Pasteurization:

Developed a process in which
liquids are heated (at 65
o
C) to kill most bacteria
responsible for spoilage.


Disease Causes
: Identified three different
microbes that caused silkworm diseases.


Vaccine:
Developed a vaccine for rabies from
dried spinal cords of infected rabbits.



Directed Pasteur Institute until his death in 1895.







History of Microbiology

Golden Age: 1857
-
1914

Germ Theory of Disease:
Belief that microbes
cause diseases. Before, most people believed
diseases were caused by divine punishment,
poisonous vapors, curses, witchcraft, etc.


Agostino Bassi (1835):

Found that a fungus was
responsible for a silkworm disease.


Ignaz Semmelweis (1840s):

Demonstrated that
childbirth fever was transmitted from one patient
to another, by physicians who didn’t disinfect their
hands. He was ostracized by colleagues.








History of Microbiology

Golden Age: 1857
-
1914

Germ Theory of Disease:


Joseph Lister (1860):

Used disinfectant to treat
surgical wounds, greatly reducing infection rates.
Considered the father of antiseptic surgery.


Robert Koch (1876):
First person to conclusively
prove that a specific bacterium caused a disease.


Germ Theory
: One microbe causes one specific
disease.



Proved that
Bacillus anthracis

causes anthrax in cattle.



Later identified bacterium that causes tuberculosis.







History of Microbiology

Modern Microbiology: After 1914

Chemotherapy:
Treatment of a disease by using a
chemical substance. Chemical must be more
poisonous to microbe than host.


Quinine
: First known chemical to treat a disease
(malaria). Used by Spanish conquistadors.


Synthetic Drugs:

Made in the laboratory.


Antibiotics:
Produced naturally by fungi and
bacteria.







History of Microbiology

Modern Microbiology: After 1914


Paul Ehrlich (1910
): Search for “
magic bullet
”.


Discovered salvarsan, an arsenic derivative, was
effective against syphilis.


Alexander Fleming (1928)
: Discovered that
penicillin produced by the mold
Penicillium
notatum

was able to prevent microbial growth.


Penicillin was not mass produced until the 1940s.


Rene Dubos (1939):
Discovered two antibiotics
(gramidin and tyrocidine) produced by bacterium
(
Bacillus brevis
).







History of Microbiology

Modern Microbiology: After 1914

Problems with Chemotherapy:


Toxicity


Drug resistant microbes







Diversity of Microorganisms

I. Bacteria (Sing. Bacterium)


Small, single
-
celled (
unicellular
) organisms.


Procaryotes:

“Before nucleus”.


Lack

the following structures:


Nuclear membrane around DNA


Membrane bound organelles


Mitochondria


Chloroplasts


Golgi apparatus


Endoplasmic reticulum


Lysosomes

Kingdom Prokaryotae: Bacteria lack
nucleus and membrane bound organelles







Diversity of Microorganisms

I. Bacteria (Sing. Bacterium)


Include two groups:


Eubacteria
: Peptidoglycan cell walls.


Archaebacteria
: Lack peptidoglycan cell walls.


Shapes
: Several forms:


Bacilli
: Rod like. (Sing. Bacillus)


Cocci
: Spherical. (Sing. Coccus)


Spiral
: Corkscrew or curved


Square


Star shaped







Diversity of Microorganisms

I. Bacteria (Sing. Bacterium)


Divide by
binary fission

(not mitosis).


Source of nutrients varies:


Heterotrophs
: Consume organic chemicals.


Autotrophs
: Make their own food. Include
photosynthetic bacteria.


Motility
: Many can “swim” by using moving
appendages:


Cilia: Small hair like structures


Flagella: Large whip like structures.


Distinguish between motility and
Brownian

motion
.







Diversity of Microorganisms

II. Fungi (Sing. Fungus)


Eucaryotes:

“True nucleus”


DNA is surrounded by
nuclear membrane
.


Cells have
membrane bound organelles
:
Mitochondria, endoplasmic reticulum, etc.


Cells are
larger

than those of procaryotes.


May be unicellular or multicellular:


Unicellular
: Yeasts


Multicellular
: Molds, mushrooms


Do
not

carry out photosynthesis.


Must absorb organic nutrients from their
environment.







Diversity of Microorganisms

II. Fungi (Sing. Fungus)


Source of nutrients varies:


Saprotrophs
: Decomposers that feed on dead and
decaying matter. Most fungi are decomposers.


Parasites
: Obtain nourishment by parasitizing live
animals and plants.


Cell wall made of chitin.


May reproduce sexually or asexually.







Diversity of Microorganisms

III. Protozoa (Sing. Protozoan)


Eucaryotes:

“True nucleus”


DNA is surrounded by nuclear membrane.


Cells have membrane bound organelles and are larger
than those of procaryotes.


Unicellular


Kingdom
Protista


Sexual or asexual reproduction


Classified based on locomotion:


Pseudopods
: “False feet”. Cytoplasmic extensions.


Example: Amoeba

Protozoa Belong to Kingdom Protista:
Eucaryotic Unicellular or Simple
Multicellular Organisms







Diversity of Microorganisms

III. Protozoa (Sing. Protozoan)


Classified based on locomotion:


Flagella
: Long whip like appendages.


Example:
Trichomonas

vaginalis
,
causes
trichominiasis
, a
sexually transmitted disease.


Cilia
: Small hair like appendages


Nonmotile
: Do not move in their mature forms.


Example:
Plasmodium spp.,
causative agent of malaria.







Diversity of Microorganisms

IV. Algae (Sing. Alga)


Eucaryotes:

“True nucleus”


Photosynthetic:
Important part of food chain
because produce oxygen and carbohydrates used
by animals.


Unicellular or multicellular


Kingdom
Protista


Sexual or asexual reproduction


Cell walls composed of
cellulose


Found in aquatic environments (oceans, lakes,
rivers), soil, and in association with plants.









Diversity of Microorganisms

V. Viruses


Acellular infectious agents, not considered
living because they lack cells.


Obligate intracellular parasites
: Viruses can
only reproduce by using the cellular machinery of
other organisms.


Simple structure
:


Protein coat (
capsid
) with either DNA or RNA, but not
both.


May also have a lipid envelope.

Comparison of Cells and Viruses







Diversity of Microorganisms

VI. Multicellular Animal Parasites


Eucaryotes:

“True nucleus”


Multicellular
animals
, usually are visible to the
naked eye.


Microscopic during some stages of life cycle.


Spend part or all of their lives inside an animal
host.


Helminths

include:


Flatworms

(Platyhelminths): E.g. Tapeworm


Roundworms

(Nematodes): E.g. Ascaris, pinworm.