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The Microbial World and You


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Title: The Microbial World and You

  • The Microbial World and You

Instructor Dr. Ahmad Saleh
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)

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 worlds inhabitants by maintaining balance of
    living organisms and chemicals in our
  • Therefore, Microorganisms are essential for life
    on earth.
  • They have important beneficial biological
  • 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
  • Decomposers Soil microbes break down dead and
    decaying matter and recycle chemical elements
    that can be used by other organisms.
  • Nitrogen Fixation Some bacteria can take
    nitrogen from air and incorporate it into organic
    compounds in soil, water, and air.

Microbes in Our Lives
  • Digestion Human and many other animals have
    microorganisms in their digestive tract, that are
    essential for digestion and vitamin synthesis.
  • Cellulose digestion by ruminants (cows, rabbits,
  • Synthesis of Vitamin K (for blood clotting) and
    Vitamin B (for metabolism) in humans.
  • Synthesis of chemical products MOs have many
    commercial applications, such as the synthesis of
    acetone, organic acids, enzymes, alcohols.
  • Medicine Many antibiotics and other drugs are
    naturally synthesized by microbes.
  • Penicillin is made by a mold.
  • 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
  • Genetic engineering recombinant microbes produce
  • Medical and therapeutic products human growth
    hormone, insuline, blood clotting factor,
    recombinant vaccines, monoclonal antibodies,etc.
  • Commercial products cellulose, digestive aids,
    and drain cleaner.
  • Medical Research Microbes are well suited for
    biological and medical research for several
  • Relatively simple and small structures, easy to
  • 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.
  • 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

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
  • Thousands of people died in devastating
    epidemics, the causes of which were NOT
  • Entire families died because vaccinations and
    antibiotics were NOT available to fight
  • 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

Naming and Classifying Microorganisms
  • Linnaeus established the system of scientific
    nomenclature (naming) of organisms in 1735.
  • Latin was the language traditionally used by
  • Scientific nomenclature assigns each organism two
    names (Binomial)
  • The genus is the first name and is always
  • The specific epithet (species name) follows and
    is not capitalized.
  • Are italicized or underlined.
  • The genus is capitalized and the specific epithet
    is lower case.
  • Are Latinized and used worldwide.
  • May be descriptive or honor a scientist.

Naming and Classifying Microorganisms
  • Staphylococcus aureus
  • Describes the clustered arrangement of the cells
    (staphylo), (coccus) indicates spherical shape,
    and the golden color of the colonies (aur-).
  • Escherichia coli
  • Honors the discoverer, Theodor Escherich, and
    describes the bacteriums habitatthe large
    intestine or colon.
  • 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.

Types of Microorganisms BACTERIA (Sing.
  • Relatively Simple, single-celled (unicelluar)
  • Prokaryotic (their genetic material is not
    enclosed in nuclear membrane)
  • Prokaryotes include the bacteria and archaea
  • Bacteria appear in one of several shapes
  • Bacillus (rodlike), b. coccus (spherical),
  • spiral (corkscrew or curved),
  • some are star-shaped or square.
  • Individual bacteria may form pairs, chains,
    clusters, or other groupings.
  • Enclosed in cell walls largely composed of
    peptidoglycan (carbohydrate and protein complex).
  • Reproduce by binary fission (division into two
    equal cells)
  • For nutrition, most bacteria use organic
    chemicals derived from dead or living organisms.
  • Some bacteria produce their food by
    photosynthesis, and some can derive nutrition
    from inorganic substances.
  • Many bacteria can swim by using flagella (moving

Types of MicroorganismsARCHAEA
  • Consists of prokaryotic cells
  • If they have cell walls, they lack peptidoglycan
  • Archaea are not known to cause disease in humans.
  • Live in extreme environments
  • Are divided into three main groups
  • Methanogens produce methane as waste product
    from respiration.
  • Extreme halophiles Salt loving, live in
    extremely salty environments such as the Great
    Salt Lake and the Dead Sea.
  • Extreme thermophiles Heat loving, live in hot
    sulfurous water such as hot springs.

Types of Microorganisms FUNGI (S. Fungus)
  • Eukaryotic (have a distinct nucleus containing
    the cells genetic material surrounded by a
    nuclear membrane)
  • Organisms in kingdom Fungi may be Unicellular or
  • Multicellular fungi, such as mushroom look like
    plants, but can not carry out photosynthesis.
  • True fungi have cell walls composed of chitin.
  • The unicellular fungi, yeasts, are oval MOs that
    are larger than bacteria.
  • The most typical fungi are molds, composed of
    visible masses of filaments (hyphae) called
  • Use organic chemicals for energy, can not carry
    out photosynthesis.
  • Fungi can reproduce sexually and asexually
  • They obtain nutrients by absorbing solutions of
    organic material from environment soil, sea
    water, fresh water, or animal or plant host.
  • Organisms called slime molds have characteristics
    of both fungi and ameobas.

Types of Microorganisms PROTOZOA (S. Protozoan)
  • Unicellular, eukaryotes microbes.
  • Protozoa move by
  • Pseudopods extensions of the cytoplasm like
  • Flagella long appendages for locomotion like
  • Cilia numerous shorter appendages for locomotion
    like Paramecium.
  • Protozoa have a variety of shapes.
  • Live as free entities or as parasites (organisms
  • that derive nutrients from living hosts).
  • Absorb or ingest organic compounds from their
  • environment)
  • Protozoa can reproduce sexually and asexually.

Figure 1.1c
Types of Microorganisms ALGAE (S. Alga)
  • Photosynthetic eukaryotes
  • Have wide variety of shapes
  • Reproduce sexually and asexually.
  • Unicellular and multicelluar.
  • The cell walls of many algae, like those of
  • are composed of cellulose (a carbohydrate).
  • Algae are aundant in fresh and salt water, in
    soil, and in association with plants.
  • As photosynthesizers, algae need light, water,
    and carbon dioxide for food production and
  • Produce molecular oxygen and organic compounds
    (carbohydrates) that are used by other organisms,
    including animals.
  • They play an important role in the balance of

Types of MicroorganismsVIRUSES
  • So small that can be seen only with electron
  • Acellular (not cellular).
  • Structurally very simple, a virus particle
  • a core made only of one type of nucleic acid,
  • either DNA or RNA.consist of DNA or RNA
  • The core is surrounded by a protein coat.
  • Sometimes the coat is enclosed in a lipid
  • Viruses can reproduce only by using the cellular
    machinery of other organisms.
  • Obligatory intracellular parasites (replicate
    only when they are in a living host cell)

Multicellular Animal Parasites
  • Multicellular animal parasites are not strictly
  • They are of medical importance.
  • They are eukaryotic organisms.
  • Multicellular animals
  • Parasitic flatworms and round worms are called
  • 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
  • Bacteria (cell walls contain a protein-carbohydrat
    e complex called peptidoglycan)
  • Archaea (cell walls, if present, lack
  • Eukarya, which includes the following kingdoms
  • Protists (slime molds, protozoa, and algae)
  • Fungi (unicellular yeasts, multicellular molds,
    and mushrooms)
  • Plants (includes mosses, ferns, conifers, and
    flowering plants)
  • Animals (includes sponges, worms, insects, and

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
  • 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
  • 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

Evidence PRO and CONRedis Experiments
  • In 1668 A strong opponent of SG, Francisco Redi
    set out to demonstrate that maggots did not arise
    spontaneously from decaying meat.
  • Redi filled two jars with decaying meat.
  • The first was left unsealed the flies thaid
    their eggs on the meat, and the eggs developed
    into larvae.
  • The second jar was sealed and, because the flies
    couldnot lay their eggs on the meat, no maggots
  • Redis antagonists were not convinced they
    claimed that fresh air was needed for spontaneous
  • Redi set up a second experiment, in which
  • a jar was covered with a fine net instead of
    being sealed.
  • No larvae appeared in the gauze-covered jar, even
    though air was present.
  • Maggots appeared only when flies were allowed to
    leave eggs on the meat.
  • Redis results blowed the belief that large forms
    of life could arise from nonlife.

Evidence Pro and ConNeedhams and Spallanzanis
  • However, many scientists still believed that
    small organisms such as van Leeuwenhoeks
    animalcules were simple enough to be generated
    from nonliving material.
  • In 1745 John Needham performed an experiment
    which seemed to strengthen the SG of MOs.
  • He heated nutrient fluids (chicken broth)
  • Poured them into covered flasks
  • The cooled solution were soon teeming with
  • Needham claimed that microbes developed
    spontaneously from the fluids.
  • 20 years later, Lazzaro Spallanzani, suggested
    that MOs from the air probably had entered
    Needhams 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, Spallanzanis observations were
    criticized on the grounds that there was not
    enough oxygen in the sealed flasks to support
    microbial growth.
  • In 1858, Rudolw Virchow challenged SG with the
    concept of Biogenesis, the claim that living
    cells can arise only from preexisting living
  • In 1861 Louis Pasteur demonstrated that
    microorganisms are present in the air and can
    contaminate sterile solutions, but air itself
    does not create microbes.
  • He filled several short-necked flasks with beef
    broth and boiled them.
  • Some were left open and allowed to cool.
  • In a few days, these flasks were found to be
    contaminated with microbes.
  • The sealed after-boiling flasks were free of
  • Pasteur reasoned that microbes in the air were
    the agents responsible for contaminating
    nonliving matter.

The Theory of Biogenesis
  • Pasteur next placed broth in open-ended
    long-necked flasks and bent the necks into
    S-shaped curves.
  • The contents of these flasks were then boiled and
  • The broth of in the flasks did not decay and
    showed no signs of life.
  • Pasteurs S-shaped neck allowed air to pass into
    the flask, but trapped the airborne MOs that
    might contaminate the broth.

Figure 1.3
Pasteurs Findings
  • Pasteur showed that MOs can be present in
    nonliving matter- on solids, in liquids, and in
    the air.
  • He demonstrated that microbial life can be
    destroyed by heat and devised methods to block
    access of airborne MOs to nutrients.
  • 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
  • Pasteurs work provided evidence that MOs can not
    originate from mystical forces preset in
    nonliving materials.
  • Scientists now believe that a form of spontaneous
    generation probably did occur on primitive Earth
    when life first began.
  • Pasteur showed that microbes are responsible for

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 Pasteurs work, discoveries
  • The agents of many diseases.
  • The role of immunity in the prevention and cure
    of diseases.
  • The relationship between microbes and disease.
  • Antimicrobial drugs
  • Improved the techniques for microscopy and
    culturing microorganisms.
  • Development of vaccines and surgical techniques.
  • Studying the chemical activities of

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
  • Pasteurs 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
  • 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
  • This idea was known as the germ theory of
  • Many people did not accept this theory at that
    time, because for centuries disease was believed
    to be punishment for individuals crimes and
  • Most people in Pasteurs 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 Pasteurs work showing microbes
    are in the air, can spoil food, and cause animal
  • 1876 Robert Koch proved for the first time that
    a bacterium causes anthrax and provided the
    experimental steps, Kochs postulates, to prove
    that a specific microbe causes a specific disease.

  • 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
  • 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

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
  • 1910 Paul Ehrlich developed the first synthetic
    drug, Salvarsan, to treat syphilis. (the magic
  • 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
  • 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
  • Since then, thousands of antibiotics have been
  • 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
  • or prevention of Abt. From entering the microbe.)

Figure 1.5
Modern Developments in MicrobiologyBranches of
  • Bacteriology is the study of bacteria.
  • Began with the van Leeuwenhoeks first
    examination of tooth scrapings.
  • New pathogenic bacteria are still discovered
  • Many bacteriologists, look at the roles of
    bacteria in food and environment.
  • Mycology is the study of fungi.
  • Includes medical, agricultural, and ecological
  • 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 organisms genes, have provided new tools for
    classifying microorganisms.
  • Previously these MOs were classified according to
    a limited number of visible characteristics.

Modern Developments in MicrobiologyBranches of
  • 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 bodys
  • immune system, inhibit the replication of
    viruses and
  • are used to treat viral diseases and cancer.
  • The use of immunology to identify and classify
  • bacteria according to serotypes (variants
  • a species) based on certain components in
    the cell
  • walls of the bacteria, was proposed by
  • Lancefield in 1933.

Figure 1.4 (3 of 3)
Modern Developments in MicrobiologyBranches of
  • 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
  • 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
  • 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
  • Recombinant DNA Technology
  • In the 1960s, Paul Berg inserted animal DNA into
    bacterial DNA and the bacteria produced an animal
  • Recombinant DNA is DNA made from two different
  • Recombinant DNA technology, or genetic
    engineering, involves microbial genetics and
    molecular biology.
  • Using microbes
  • Beadle and Tatum showed that genes encode a
    cells 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
  • The vast majority of microbes benefit humans,
    other animals, and plants in many ways.
  • 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
  • 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
  • In 1988, microbes began used to clean up
    pollutants and
  • toxic wastes produced by various industrial
  • 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

UN 2.1
Microbes and Human Welfare
  • 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
  • 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
  • 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 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.
  • 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

Microbes and Human DiseaseINFECTIOUS DISEASES
  • An infectious disease is one in which pathogens
    invade a susceptible host, such as a human or
  • The pathogen carries out at least part of its
    life cycle inside the host, and disease
    frequently results.
  • When a pathogen overcomes the hosts resistance,
    disease results.
  • Many mistakenly believed that infectious diseases
    were under control
  • Malaria would be eradicated by killing mosquitoes
    by DDT.
  • A vaccine would prevent diphtheria.
  • 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
  • In addition, a number of new diseases -Emerging
    infectious diseases (EID)-have cropped up in
    recent years

Microbes and Human DiseaseEMERGING INFECTIOUS
  • 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
  • Evolutionary changes in existing organisms.
  • The spread of known diseases to new geographic
    regions or populations by modern transportation.
  • Increased human exposure to new, unusual
    infectious agents.
  • 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
  • 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
  • Escherichia coli O57H7
  • Toxin-producing strain of E. coli
  • First seen in 1982
  • Leading cause of diarrhea worldwide
  • Ebola hemorrhagic fever
  • Caused by Ebola virus
  • Causes fever, hemorrhaging, and blood clotting
  • First identified near Ebola River, Congo
  • Outbreaks every few years.
  • Invasive group A Streptococcus
  • Rapidly growing bacteria that cause extensive
    tissue damage
  • Increased incidence since 1995
  • Avian influenza A (H5N1)
  • Caused by Influenza A virus (H5N1)
  • Primarily in waterfowl and poultry
  • Sustained human-to-human transmission has not
    occurred yet

Emerging Infectious Diseases
  • Severe acute respiratory syndrome (SARS)
  • SARS-associated Coronavirus
  • Occurred in 2002-2003
  • Person-to-person transmission
  • Cryptosporidiosis
  • Caused by Cryptosporidium protozoa
  • First reported in 1976
  • Causes 30 of diarrheal illness in developing
  • In the United States, transmitted via water
  • Acquired immunodeficiency syndrome (AIDS)
  • Caused by Human immunodeficiency virus (HIV)
  • First identified in 1981
  • Worldwide epidemic infecting 44 million people
    14,000 new infections daily
  • Sexually transmitted disease affecting males and
  • In the United States, HIV/AIDS cases 30 are
    female and 75 are African American
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