M I C R O B I O L O G Ya n i n t r o d u c t i o n

ninth edition TORTORA FUNKE CASE

1The Microbial

World and You

Instructor : Dr. Ahmad Saleh

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:

1. Bacteria

2. Fungi (yeasts and molds)

3. Microscopic Algae

4. Protozoa

5. Viruses, Viroids, Prions

(Non-living infectious agents)

Microbes in Our Lives

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.

Microbes in Our Lives

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.

Microbes in Our Lives

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.

Microbes in Our Lives

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

1. Prevent disease occurrence

2. Prevent food spoilage

3. Led to aseptic techniques to prevent contamination in

medicine and in microbiology laboratories.

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.

Naming and Classifying Microorganisms

1. Staphylococcus aureus

Describes the clustered arrangement of the cells (staphylo),

(coccus) indicates spherical shape, and the golden color of

the colonies (aur-).

2. Escherichia coli

Honors the discoverer, Theodor Escherich, and describes the

bacterium’s habitat–the large intestine or colon.

3. After the first use, scientific names may be abbreviated with the

first letter of the genus and the specific epithet:

Staphylococcus aureus and Escherichia coli are found in the

human body. S. aureus is on skin and E. coli in the large

intestine.

Naming and Classifying Microorganisms

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),

c. spiral (corkscrew or curved),

d. 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).

Types of MicroorganismsARCHAEA

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.

Types of Microorganisms 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.

Types of Microorganisms 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.

Figure 1.1c

Types of Microorganisms 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.

Types of MicroorganismsVIRUSES

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

b. The core is surrounded by a protein coat.

c. 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.

Figure 12.28a

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).

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.

A Brief History of Microbiology

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 CONRedi’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 ConNeedham’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.

Figure 1.3

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 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.

The Golden Age of Microbiology

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.

The Germ Theory of Disease

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.

The Birth of Modern Chemotherapy

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.) Figure 1.5

Modern Developments in MicrobiologyBranches 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.

Figure 1.4 (3 of 3)

Modern Developments in MicrobiologyBranches of Microbiology

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.

Modern Developments in MicrobiologyBranches of Microbiology

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).

Modern Developments in MicrobiologyBranches of Microbiology

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.

Microbes and Human Welfare

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. UN 2.1

Microbes and Human Welfare

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.

Microbes and Human Welfare

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 Welfare

Microbes and Human DiseaseNORMAL 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.

1. Some protect us against disease by preventing the over-growth

of harmful microbes.

2. 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.

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

Microbes and Human DiseaseINFECTIOUS 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

a. Caused by prion

b. Also causes Creutzfeldt-Jakob disease (CJD)

c. New variant CJD in humans is related to cattle feed from infected

sheep.

Microbes and Human DiseaseEMERGING INFECTIOUS DISEASES

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

Emerging Infectious Diseases

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