Microbiology

Microbiology
The Microbial World and You
Microbes in Our Lives
 Microbiology is the study of microorganisms.
 The overall theme of the Microbiology course is to study the relationship between
microbes and our lives.
 Microorganisms (microbes) are organisms that are too small to be seen with the
unaided eye, and usually require a microscope to be seen.
 This relationship involves harmful effects such as diseases and food spoilage as well as
many beneficial effects.
 “Germ” refers to a rapidly growing cell.
 Microorganisms include:
 Bacteria
 Fungi (yeasts and molds)
 Microscopic Algae
 Protozoa
 Viruses, Viroids, Prions
(Non-living infectious agents)
Prepared by Amjad Khan

 These small organisms are usually associated with major diseases such as AIDS,
uncomfortable infections, or food spoilage.
 However, the majority of microorganisms make crucial contributions to the to the welfare
of the world’s inhabitants by maintaining balance of living organisms and chemicals in
our environment.
 Therefore, Microorganisms are essential for life on earth.
 They have important beneficial biological functions:
1. Photosynthesis: Marine and freshwater MO (Algae and some bacteria) capture
energy from sunlight and convert it to food, forming the basis of the food chain in
oceans, lakes, and rivers and generates oxygen which is critical for life on Earth.
2. Decomposers: Soil microbes break down dead and decaying matter and recycle
chemical elements that can be used by other organisms.
3. Nitrogen Fixation: Some bacteria can take nitrogen from air and incorporate it
into organic compounds in soil, water, and air.
4. Digestion: Human and many other animals have microorganisms in their digestive tract,
that are essential for digestion and vitamin synthesis.
a. Cellulose digestion by ruminants (cows, rabbits, etc.)
b. Synthesis of Vitamin K (for blood clotting) and Vitamin B (for
metabolism) in humans.
5. Synthesis of chemical products: MOs have many commercial applications, such as the
synthesis of acetone, organic acids, enzymes, alcohols.
6. Medicine: Many antibiotics and other drugs are naturally synthesized by microbes.
 Penicillin is made by a mold.
7. Food industry: many important foods and beverages are made with microbes: vinegar,
pickles, alcoholic beverages, green olives, soy sauce, buttermilk, cheese, yogurt, and
bread.
8. Genetic engineering: recombinant microbes produce important
a. Medical and therapeutic products: human growth hormone, insuline, blood
clotting factor, recombinant vaccines, monoclonal antibodies,…etc.
b. Commercial products: cellulose, digestive aids, and drain cleaner.

9. Medical Research: Microbes are well suited for biological and medical research for
several reasons:
a. Relatively simple and small structures, easy to study
b. Genetic material is easily manipulated.
c. Can grow a large number of cells very quickly and at low cost.
d. Short generation times make them very useful to study genetic changes.
 Though only a minority of MOs are pathogenic (disease-producing), practical knowledge
of microbes is necessary for medicine and related heath sciences.
 Ex.: Hospital workers must be able to protect patients from common microbes
that are normally harmless but pose a threat to the sick and injured.
Knowledge of Microorganisms
 Today we understand that MOs are almost everywhere !
 Yet not long ago, before the invention of the microscope, microbes were unknown to
scientists and :
 Thousands of people died in devastating epidemics, the causes of which were
NOT understood.
 Entire families died because vaccinations and antibiotics were NOT available to
fight infections.
 Therefore, knowledge of MOs allows humans to
 Prevent disease occurrence
 Prevent food spoilage
 Led to aseptic techniques to prevent contamination in medicine and in
microbiology laboratories.
Naming and Classifying Microorganisms

 Linnaeus established the system of scientific nomenclature (naming) of organisms in
1735.
 Latin was the language traditionally used by scholars.
1. Scientific nomenclature assigns each organism two names (Binomial):
a. The genus is the first name and is always capitalized.
b. The specific epithet (species name) follows and is not capitalized.
2. Are italicized or underlined.
3. The genus is capitalized and the specific epithet is lower case.
4. Are “Latinized” and used worldwide.
5. May be descriptive or honor a scientist.
6. Staphylococcus aureus
a. Describes the clustered arrangement of the cells (staphylo), (coccus) indicates
spherical shape, and the golden color of the colonies (aur-).
7. Escherichia coli
a. Honors the discoverer, Theodor Escherich, and describes the bacterium’s habitat–
the large intestine or colon.
8. After the first use, scientific names may be abbreviated with the first letter of the genus
and the specific epithet:
a. Staphylococcus aureus and Escherichia coli are found in the human body. S.
aureus is on skin and E. coli in the large intestine.
Types of Microorganisms
BACTERIA (Sing. Bacterium)
1. Relatively Simple, single-celled (unicelluar) organisms.
2. Prokaryotic (their genetic material is not enclosed in nuclear membrane)
 Prokaryotes include the bacteria and archaea
3. Bacteria appear in one of several shapes:
a. Bacillus (rodlike), b. coccus (spherical),

b. spiral (corkscrew or curved),
c. some are star-shaped or square.
4. Individual bacteria may form pairs, chains, clusters, or other groupings.
5. Enclosed in cell walls largely composed of peptidoglycan (carbohydrate and protein
complex).
6. Reproduce by binary fission (division into two equal cells)
7. For nutrition, most bacteria use organic chemicals derived from dead or living organisms.
8. Some bacteria produce their food by photosynthesis, and some can derive nutrition from
inorganic substances.
9. Many bacteria can swim by using flagella (moving appendages).
ARCHAEA
1. Consists of prokaryotic cells
2. If they have cell walls, they lack peptidoglycan
3. Archaea are not known to cause disease in humans.
4. Live in extreme environments
5. Are divided into three main groups:
a. Methanogens: produce methane as waste product from respiration.
b. Extreme halophiles: Salt loving, live in extremely salty environments such as the
Great Salt Lake and the Dead Sea.
c. Extreme thermophiles: Heat loving, live in hot sulfurous water such as hot
springs.

FUNGI (S. Fungus)
1. Eukaryotic (have a distinct nucleus containing the cell’s genetic material surrounded by a
nuclear membrane)
2. Organisms in kingdom Fungi may be Unicellular or multicellular
3. Multicellular fungi, such as mushroom look like plants, but can not carry out
photosynthesis.
4. True fungi have cell walls composed of chitin.
5. The unicellular fungi, yeasts, are oval MOs that are larger than bacteria.
6. The most typical fungi are molds, composed of visible masses of filaments (hyphae)
called mycelia.
7. Use organic chemicals for energy, can not carry out photosynthesis.
8. Fungi can reproduce sexually and asexually
9. They obtain nutrients by absorbing solutions of organic material from environment – soil,
sea water, fresh water, or animal or plant host.
10. Organisms called slime molds have characteristics of both fungi and ameobas.
PROTOZOA (S. Protozoan)
1. Unicellular, eukaryotes microbes.
2. Protozoa move by:

a. Pseudopods: extensions of the cytoplasm like Ameoba.,
b. Flagella: long appendages for locomotion like Trypanosoma.
c. Cilia: numerous shorter appendages for locomotion like Paramecium.
3. Protozoa have a variety of shapes.
4. Live as free entities or as parasites (organisms
that derive nutrients from living hosts).
5. Absorb or ingest organic compounds from their
environment)
6. Protozoa can reproduce sexually and asexually.
ALGAE (S. Alga)
1. Photosynthetic eukaryotes
2. Have wide variety of shapes
3. Reproduce sexually and asexually.
4. Unicellular and multicelluar.
5. The cell walls of many algae, like those of plants,
are composed of cellulose (a carbohydrate).
6. Algae are aundant in fresh and salt water, in soil, and in association with plants.
7. As photosynthesizers, algae need light, water, and carbon dioxide for food production
and growth.

8. Produce molecular oxygen and organic compounds (carbohydrates) that are used by other
organisms, including animals.
9. They play an important role in the balance of nature.
VIRUSES
1. So small that can be seen only with electron microscope.
2. Acellular (not cellular).
3. Structurally very simple, a virus particle contains
a. a core made only of one type of nucleic acid,
either DNA or RNA.consist of DNA or RNA core
a. The core is surrounded by a protein coat.
b. Sometimes the coat is enclosed in a lipid envelope.
4. Viruses can reproduce only by using the cellular machinery of other organisms.
5. Obligatory intracellular parasites (replicate only when they are in a living host cell)
Multicellular Animal Parasites
1. Multicellular animal parasites are not strictly MOs.
2. They are of medical importance.
3. They are eukaryotic organisms.

4. Multicellular animals
5. Parasitic flatworms and round worms are called helminths.
6. During some stages of their life cycles, helminths are microscopic in size.
Classification of Microorganisms
 Before the existence of microbes was known, all organisms were grouped into either the
animal kingdom or the plant kingdom.
 In 1978, Carl Woese, devised a system of classification based on the cellular
organization of organisms.
 It groups all organisms in three domains as follows:
1. Bacteria (cell walls contain a protein-carbohydrate complex called peptidoglycan)
2. Archaea (cell walls, if present, lack peptidoglycan)
3. Eukarya, which includes the following kingdoms:
a. Protists (slime molds, protozoa, and algae)
b. Fungi (unicellular yeasts, multicellular molds, and mushrooms)
c. Plants (includes mosses, ferns, conifers, and flowering plants)
d. Animals (includes sponges, worms, insects, and vertebrates).
A Brief History of Microbiology
 The science of Microbiology dates back only two hundred years.
 However, microorganisms have been around for thousands of years.
 Ancestors of bacteria were the first living cells to appear on Earth.

 The first microbes (animalcules) were observed in 1673 by Leeuwenhoek.
 In 1665, Robert Hooke reported that living things were composed of little boxes or cells,
with the help of a relatively crude
microscope.
 In 1858, Rudolf Virchow said cells arise from
preexisting cells.
 Cell theory: All living things are composed of cells
and come from preexisting cells.
 1673-1723: Antoni van Leeuwenhoek described live
microorganisms (animalcules) that he observed in
teeth scrapings, rain water.
The Debate Over Spontaneous Generation
 After van Leeuwenhoek discovered the “invisible” world of microorganisms, the
scientific community of that time became interested in the origins of these tiny living
things.
 Not much more than 100 years ago, many scientists and philosophers believed that some
forms of life could arise spontaneously from nonliving matter, they called this the
hypothesis of spontaneous generation.
 Therefore, people commonly believed that toads, snakes, and mice could be born of moist
soil; that flies could emerge from manure; and that maggots, the larvae of flies, could
arise from decaying corpses.
 According to spontaneous generation, a “vital force” forms life.

 The alternative hypothesis, that the living organisms arise from preexisting life, is called
biogenesis.
Evidence PRO and CON
Redi’s Experiments
A. In 1668: A strong opponent of SG, Francisco Redi set out to demonstrate that maggots
did not arise spontaneously from decaying meat.
1. Redi filled two jars with decaying meat.
2. The first was left unsealed; the flies thaid their eggs on the meat, and the eggs
developed into larvae.
3. The second jar was sealed and, because the flies couldnot lay their eggs on the
meat, no maggots appeared.
 Redi’s antagonists were not convinced; they claimed that fresh air was needed for
spontaneous generation.
 Redi set up a second experiment, in which
1. a jar was covered with a fine net instead of being sealed.
2. No larvae appeared in the gauze-covered jar, even though air was present.
3. Maggots appeared only when flies were allowed to leave eggs on the meat.
 Redi’s results blowed the belief that large forms of life could arise from nonlife.
Evidence Pro and Con
Needham’s and Spallanzani’s Exp.
 However, many scientists still believed that small organisms such as van Leeuwenhoek’s
“animalcules” were simple enough to be generated from nonliving material.
B. In 1745: John Needham performed an experiment which seemed to strengthen the SG of
MOs.
1. He heated nutrient fluids (chicken broth)
2. Poured them into covered flasks

3. The cooled solution were soon teeming with microorganisms.
4. Needham claimed that microbes developed spontaneously from the fluids.
C. 20 years later, Lazzaro Spallanzani, suggested that MOs from the air probably had
entered Needham’s solutions after they were boiled.
 Spallanzani showed that nutrients fluids heated after being sealed in a flask did
not develop microbial growth.
 Needham responded by claiming the “vital force” was destroyed by heat and kept
out of the flasks by the seals.
Evidence Pro and Con
 The “ vital force” principle was strengthened when Anton Lavoisier showed the
importance of oxygen to life.
 Therefore, Spallanzani’s observations were criticized on the grounds that there was not
enough oxygen in the sealed flasks to support microbial growth.
D. In 1858, Rudolw Virchow challenged SG with the concept of Biogenesis, the claim that
living cells can arise only from preexisting living cells.
E. In 1861: Louis Pasteur demonstrated that microorganisms are present in the air and can
contaminate sterile solutions, but air itself does not create microbes.
1. He filled several short-necked flasks with beef broth and boiled them.
2. Some were left open and allowed to cool.
3. In a few days, these flasks were found to be contaminated with microbes.
4. The sealed after-boiling flasks were free of microorganisms.
5. Pasteur reasoned that microbes in the air were the agents responsible for
contaminating nonliving matter.
The Theory of Biogenesis
1. Pasteur next placed broth in open-ended long-necked flasks and bent the necks into S-
shaped curves.
2. The contents of these flasks were then boiled and cooled.
3. The broth of in the flasks did not decay and showed no signs of life.

4. Pasteur’s S-shaped neck allowed air to pass into the flask, but trapped the airborne MOs
that might contaminate the broth.
Pasteur’s Findings
1. Pasteur showed that MOs can be present in nonliving matter- on solids, in liquids, and in
the air.
2. He demonstrated that microbial life can be destroyed by heat and devised methods to
block access of airborne MOs to nutrients.
3. These discoveries forms the basis of aseptic techniques (techniques that prevent
contamination by unwanted MOs.), which are now the standard practice in laboratory and
many medical procedures.
4. Pasteur’s work provided evidence that MOs can not originate from mystical forces preset
in nonliving materials.
5. Scientists now believe that a form of spontaneous generation probably did occur on
primitive Earth when life first began.
6. Pasteur showed that microbes are responsible for fermentation.
The Golden Age of Microbiology
 The period from 1857-1914, has been named the Golden Age of Microbiology.
 During this period, rapid advances headed by Pasteur and Robert Koch, led to the
establishment of microbiology as a science.
 Beginning with Pasteur’s work, discoveries included
1. The agents of many diseases.
2. The role of immunity in the prevention and cure of diseases.

3. The relationship between microbes and disease.
4. Antimicrobial drugs
5. Improved the techniques for microscopy and culturing microorganisms.
6. Development of vaccines and surgical techniques.
7. Studying the chemical activities of microorganisms.
Fermentation and Pasteurization
 At that time, many scientists believed that air converted the sugars in beverages into
alcohols.
 Pasteur found instead that microbes called yeasts convert the sugars to alcohols in the
absence of air in a process called fermentation.
 Fermentation is the conversion of sugar to alcohol to make beer and wine.
 Souring and spoilage are caused by different MOs called bacteria.
 In the presence of air, bacteria change the alcohol in the beverage into vinegar (acetic
acid).
 Pasteur’s solution to the spoilage problem was to heat the beer and wine just enough to
kill most of the bacteria that caused the spoilage in a process called pasteurization.
 Pasteurization is now commonly used to reduce spoilage and kill potentially harmful
bacteria in milk as well as in some alcoholic drinks.
 Showing the connection between spoilage of food and MOs was a major step towards
establishing the relationship between disease and microbes.
The Germ Theory of Disease
 Until relatively recently, the fact that many kinds of diseases are related to MOs was
unknown.
 Before the time of Pasteur, effective treatments for many diseases were discovered by
trial and error, but the causes of the diseases were unknown.
 The realization that yeasts play a crucial role in fermentation was the first link between
the activity of a MO and physical and chemical changes in organic materials.

 This discovery alerted scientists that MOs might have similar relationships with plants
and animals- specially, that MOs might cause diseases.
 This idea was known as the germ theory of disease.
 Many people did not accept this theory at that time, because for centuries disease was
believed to be punishment for individual’s crimes and misdeeds.
 Most people in Pasteur’s time found it inconceivable that “invisible” microbes could
travel through the air to infect plants and animals, or remain on clothing and bedding to
be transmitted from one person to another.
 1835: Agostino Bassi showed that a silkworm disease was caused by a fungus.
 1865: Pasteur found that another recent silkworm disease was caused by a protozoan.
 1840s: Ignaz Semmelwise advocated hand washing to prevent transmission of childbirth
fever from one obstetrical patient to another.
 1860s: Joseph Lister used a chemical disinfectant (phenol) to prevent surgical wound
infections after looking at Pasteur’s work showing microbes are in the air, can spoil food,
and cause animal diseases.
 1876: Robert Koch proved for the first time that a bacterium causes anthrax and
provided the experimental steps, Koch’s postulates, to prove that a specific microbe
causes a specific disease.
Vaccination
 1796: Edward Jenner found a way to protect people from smallpox almost 70 years
before Koch established that microorganism causes anthrax.
 He inoculated a healthy 8-years-old volunteer with cowpox virus. The person was then
protected from cowpox and smallpox.
 The process was called Vaccination, derived from Latine word vacca for cow.
 The protection from disease provided by vaccination or by recovery from the disease
itself is called immunity.

 In about 1880, Pasteur discovered why vaccination work by working on cholera
vaccination.
 Pasteur used the term vaccine for cultures of avirulent microorganisms used for
preventive inoculation.
 Some vaccines are still produced from avirulent microbial strains, others are made from
killed virulent microbes, from isolated components of virulent MOs, or by genetic
engineering techniques.
The Birth of Modern Chemotherapy
 Treatment of disease by using chemical substances is called chemotherapy.
 Chemotherapeutic agents prepared from chemicals in the laboratory are called synthetic
drugs.
 Chemotherapeutic agents produced naturally by bacteria and fungi to act against other
MOs are called antibiotics.
 The success of chemotherapy is based on the fact that some chemicals are more
poisonous to MOs than to the hosts infected by the microbes.
 Quinine from tree bark was long used to treat malaria.
 1910: Paul Ehrlich developed the first synthetic drug, Salvarsan, to treat syphilis. (the
magic bullet!)
 1930s: Several other synthetic drugs derived from dyes that could destroy MOs were
developed.
 Sulfonamides (sulfa drugs) were synthesized at about the same time.
 1928: Alexander Fleming discovered the first antibiotic.
 On a contaminated plate, around the mold (Penicillium) was a clear area where
bacterial growth had been inhibited.
 He observed that the Penicillium mold made an antibiotic, penicillin, that killed S.
aureus.
 1940s: Penicillin was tested clinically and mass produced.
 Since then, thousands of antibiotics have been discovered.

 Antibiotics and other chemotherapeutic drug faces many problem:
 Toxicity to humans in practical use, specially
antiviral drugs (why ?)
 The emergence and spread of new varieties
of MOs that are resistant to antibiotics.
(due to bacterial enzymes that inactivate antibiotics,
or prevention of Abt. From entering the microbe.)
Modern Developments in Microbiology
Branches of Microbiology
 Bacteriology is the study of bacteria.
 Began with the van Leeuwenhoek’s first examination of tooth scrapings.
 New pathogenic bacteria are still discovered regularly.
 Many bacteriologists, look at the roles of bacteria in food and environment.
 Mycology is the study of fungi.
 Includes medical, agricultural, and ecological branches.
 Fungal infections accounting for 10% of hospital acquired infections.
 Parasitology is the study of protozoa and parasitic worms.
 Recent advances in genomics, the study of all of an organism’s genes, have provided new
tools for classifying microorganisms.

 Previously these MOs were classified according to a limited number of visible
characteristics.
 Immunology is the study of immunity.
 Vaccines and interferons are being investigated to prevent and cure viral diseases.
 Vaccines are now available for numerous diseases, including measles, rubella (German
measles), mumps, chickenpox, pneumococcal pneumonia, tetanus, tuberculosis,
whooping coughs, polio, and hepatitis B.
 Smallpox was eradicated due to effective vaccination and polio is expected to.
 Interferons, substances produced by the body’s own
immune system, inhibit the replication of viruses and
are used to treat viral diseases and cancer.
 The use of immunology to identify and classify some
bacteria according to serotypes (variants within
a species) based on certain components in the cell
walls of the bacteria, was proposed by Rebecca
Lancefield in 1933.
 Virology is the study of viruses.
 In 1892, Dimitri Iwanowski reported that the
organism that caused mosaic disease of tobacco was so small that is passed the
bacterial filters.
 In 1935, Wendell Stanely demonstrated that the organism , called tobacco mosaic
virus (TMV), was different from other microbes, so simple, and composed of only
nucleic acid core and protein core.

 In 1940s, the development of electron microscope enabled the scientists to
observe the structure and activity of viruses in detail.
 Recombinant DNA Technology:
 In the 1960s, Paul Berg inserted animal DNA into bacterial DNA and the bacteria
produced an animal protein.
 Recombinant DNA is DNA made from two different sources.
 Recombinant DNA technology, or genetic engineering, involves microbial
genetics and molecular biology.
 Using microbes
 Beadle and Tatum showed that genes encode a cell’s enzymes (1942).
 Avery, MacLeod, and McCarty showed that DNA was the hereditary material
(1944).
 Lederberg and Tatum discovered that genetic material could be transferred from
one bacterium to another by conjugation (1946).
 Watson and Crick proposed a model for the structure of DNA (1953).
 Jacob and Monod discovered the role of mRNA in protein synthesis (1961).
Microbes and Human Welfare
 Only minority of all MOs are pathogenic.
 Microbes that cause food spoilage are also a minority.
 The vast majority of microbes benefit humans, other animals, and plants in many ways.
 RECYCLING VITAL ELEMENTS
 In 1880s, Beijerinck and Winogradsky showed how bacteria help recycle vital elements
between the soil and the atmosphere.
 Microbial ecology: the study of the relationship between microorganisms and their
environment.
 Microorganisms recycle carbon, nitrogen, sulfur, oxygen, and phosphorus into forms that
can be used by plants and animals.

 Bacteria and fungi, return CO2 to the atmosphere when decomposing organic wastes and
dead plants and animals.
 Algae, cyanobacteria, and plants use CO2 to produce carbohydrates.
 SEWAGE TREATMENT: Using microbes to recycle water.
 Recycling water and prevent the pollution of rivers and oceans
 Bacteria degrade organic matter in sewage (99% water), producing such by-
products as carbon dioxide, nitrates, phosphates, sulfates, ammonia, hydrogen
sulfide, and methane.
 BIOREMEDIATION: Using microbes to clean up pollutants.
 In 1988, microbes began used to clean up pollutants and
toxic wastes produced by various industrial processes.
 Bacteria degrade or detoxify pollutants such as oil and
mercury.
 In addition, bacterial enzymes are used in drain
cleaners to remove clogs
 Such bioremedial microbes are Pseudomonas and
Bacillus, their enzymes used in household detergents.
 INSECT BEST CONTROL BY MOs
 Insect pest control is important for both agriculture
and the prevention of human diseases.
 Bacillus thuringiensis infections are fatal for many insects but harmless to other
animals, including humans, and to plants.
 The bacteria produce protein crystals that are toxic to the digestive systems of the
insects.

 The toxin gene has been inserted into some plants to make them insect resistant.
 Microbes that are pathogenic to insects are alternatives to chemical pesticides in
preventing insect damage to agricultural crops, disease transmission, and avoid
harming the environment.
 MODERN BIOTECHNOLOGY AND RECOMBINANT DNA TECHNOLOGY
 Biotechnology, the use of microbes to produce foods and chemicals, is centuries old.
 Genetic engineering is a new technique for biotechnology. Through genetic engineering,
bacteria and fungi can produce a variety of proteins including vaccines and enzymes.
 Recombinant DNA techniques have been used to produce a number of natural proteins,
vaccines, and enzymes.
 The very exciting and important outcome of recombinant DNA techniques is
 Gene Therapy: inserting a missing gene or replacing a defective one in human cells by
using a harmless virus to carry the missing or new gene into certain host cells.
 Genetically modified bacteria are used to protect crops from insects, from freezing, and
to improve the appearance, flavor, and shelf life of fruits and vegetables. (more: Drought
resistance and temperature tolerance)
Microbes and Human Disease
NORMAL MICROBIOTA
 We all live in a world filled with microbes, and we all have a variety of microorganisms
on and in our bodies.
 Microbes normally present in and on the human body are called normal microbiota, or
flora.
 Bacteria were once classified as plants giving rise to use of the term flora for
microbes.
 This term has been replaced by microbiota.
 The normal microbiota not only harmless, but also benefit us.
 Some protect us against disease by preventing the over-growth of harmful
microbes.
 Others produce useful substances such as vitamine K and B.

 Unfortunately, under some circumstances normal microbiota can make us sick or infect
people we contact.
INFECTIOUS DISEASES
 An infectious disease is one in which pathogens invade a susceptible host, such as a
human or animal.
 The pathogen carries out at least part of its life cycle inside the host, and disease
frequently results.
 When a pathogen overcomes the host’s resistance, disease results.
 Many mistakenly believed that infectious diseases were under control
a. Malaria would be eradicated by killing mosquitoes by DDT.
b. A vaccine would prevent diphtheria.
c. Improved sanitation measures would help prevent cholera transmission.
 Recent outbreaks of such infectious diseases indicates that not only they are not
disappearing, but seem to be reemerging and increasing.
 In addition, a number of new diseases -Emerging infectious diseases (EID)-have cropped
up in recent years
EMERGING INFECTIOUS DISEASES
 Emerging infectious diseases (EID): are diseases that are new or changing and are
increasing or have the potential to increase in incidence in the near future.
 Some factors that have contributed to the emergence of EIDs:
a. Evolutionary changes in existing organisms.
b. The spread of known diseases to new geographic regions or populations by
modern transportation.

c. Increased human exposure to new, unusual infectious agents.
1. West Nile encephalitis
 Caused by West Nile virus
 First diagnosed in the West Nile region of Uganda in 1937
 Appeared in New York City in 1999
2. Bovine spongiform encephalopathy
 Caused by prion
 Also causes Creutzfeldt-Jakob disease (CJD)
 New variant CJD in humans is related to cattle feed from infected sheep.
Emerging Infectious Diseases
3. Escherichia coli O57:H7
a. Toxin-producing strain of E. coli
b. First seen in 1982
c. Leading cause of diarrhea worldwide
4. Ebola hemorrhagic fever
a. Caused by Ebola virus
b. Causes fever, hemorrhaging, and blood clotting
c. First identified near Ebola River, Congo
d. Outbreaks every few years.
5. Invasive group A Streptococcus
a. Rapidly growing bacteria that cause extensive tissue damage
b. Increased incidence since 1995
6. Avian influenza A (H5N1)
a. Caused by Influenza A virus (H5N1)
b. Primarily in waterfowl and poultry

c. Sustained human-to-human transmission has not occurred yet
7. Severe acute respiratory syndrome (SARS)
a. SARS-associated Coronavirus
b. Occurred in 2002-2003
c. Person-to-person transmission
8. Cryptosporidiosis
a. Caused by Cryptosporidium protozoa
b. First reported in 1976
c. Causes 30% of diarrheal illness in developing countries
d. In the United States, transmitted via water
9. Acquired immunodeficiency syndrome (AIDS)
a. Caused by Human immunodeficiency virus (HIV)
b. First identified in 1981
c. Worldwide epidemic infecting 44 million people; 14,000 new infections daily
d. Sexually transmitted disease affecting males and females
e. In the United States, HIV/AIDS cases: 30% are female and 75% are African
American.
Act as if you were to die
tomorrow, work as if you
were to live for ever

THE END

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