Plants and Fungi Used to Treat Infectious Disease

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Plants and Fungi Used to Treat Infectious Disease
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Infectious Disease

• World wide, infectious disease is the number one
  cause of death accounting for approximately
  one-half of all deaths in tropical countries
• Infectious disease mortality rates are actually
  increasing in developed countries, such as US
• Death from infectious disease, ranked 5th in
  1981, has become the 3rd leading cause of death
  in 1992
• Infectious disease underlying cause of death in
  8 of deaths occurring in US

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Terms

• Antimicrobial a substance which destroys or
  inhibits the growth of microorganisms
• Antiseptic a substance that checks the growth
  or action of microorganisms especially in or on
  living tissue
• Antibiotic a substance produced by or derived
  from a microorganism and able to inhibit or kill
  another microorganism

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Antibiotics vs Antimicrobials

• Antibiotics are toxic to microorganisms
• Produced by fungi and/or bacteria
• In the natural environment, antibiotics give the
  producing organism advantages over competing
  microorganisms for available nutrients and space
• First antibiotic put into large-scale production
  was penicillin

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Antibiotics vs Antimicrobials

• Antimicrobials produced by a variety of organisms
  including many plants
• Plant-based antimicrobials provide protection for
  the plant against pathogenic bacteria or fungi
• Plant-based antimicrobials represent a vast
  untapped source for medicines
• Plants-based antimicrobials have enormous, but
  largely untapped, therapeutic potential for
  treating infectious disease

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Overview

• Antibiotics from fungi
• Antimalarials from plants
• Other antimicrobials from plants

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Penicillin

• By-product of certain Penicillium species
• Inhibits the growth of gram-positive bacteria
• Blocks wall synthesis in bacteria and results in
  death of the bacterial cell by lysis
• Surpassed known therapeutic agents by suppressing
  bacterial growth without being toxic

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Discovery of Penicillin

• Infusions of moldy bread, cheese, meat, and
  soybeans have long history as folk treatment for
  wounds
• 19th Century observations of antibiosis by
  Penicillium spp
• Roberts - 1874
• Tyndall - 1881
• others

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Discovery of Penicillin

• First discovered in 1928 by British physician
  Alexander Fleming
• Accidental discovery of a contaminated bacterial
  culture
• Fungus Penicillium notatum killed the culture of
  Staphylococcus aureus growing in the petri dish

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Sir Alexander Fleming
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Flemings Petri Dish
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Zone of Inhibition

• Around the fungal colony is a clear zone where no
  bacteria are growing
• Zone of inhibition due to the diffusion of a
  substance with antibiotic properties from the
  fungus

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Additional work

• Fleming carried out additional experiments, named
  it penicillin and published his findings
• Fleming's paper attracted little attention at the
  time
• Flemings experiments at purifying penicillin
  failed
• It was 11 yrs before research advanced

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Research at Oxford University

• In 1939, Howard Florey and Ernst Chain began
  investigating naturally occurring antibacterial
  compounds and came across Fleming's report on
  penicillin
• Within a year, the team at Oxford had chemically
  analyzed the compound and demonstrated that it
  could destroy certain types of bacteria in test
  tubes

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Progress Continues

• War in Europe was escalating and Florey and Chain
  realized the potential for treating war wounds
• Tests on infected animals were successful
• 1941 the first human tests were conducted
• Research was moved to various sites in the United
  States because of the war
• Really miraculous cures were reported in human
  tests, and mass production was finally achieved

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USDA North Regional Research Lab

• One team of researchers was looking for more
  high-yielding sources of penicillin
• Moldy fruits and vegetables were routinely
  collected from local groceries stories
• Fungi were isolated and tested for antibiotic
  production

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Summer of 1943

• Cantaloupe was found contaminated with
  Penicillium chrysogenum.
• The fungus produced 200 times more penicillin
  than Fleming's isolate.
• This species was used in the industrial
  production of the drug and continues to be used
  today

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Mass Production Achieved

• By D-Day in 1944, there was enough penicillin to
  treat all British and American casualties of the
  European invasion
• By the time World War II ended, sufficient
  penicillin was available for civilian use
• In 1945 Florey, Chain, and Fleming received the
  Nobel Prize for their work in developing the
  first "miracle" drug

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Start of Synthetics

• Soon after World War II, the pharmaceutical
  industry developed chemically altered versions of
  the penicillin molecule
• Modified penicillins provided for greater
  stability, broader anti-bacterial activity, and
  also oral administration which would permit home
  use of antibiotics

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Penicillin Today

• Still the most widely used antibiotic
• Still the drug of choice to treat many bacterial
  infections
• Scientists have continued to improve the yield of
  the drug
• Present day strains of P. chrysogenum are
  biochemical mutants that produce 10,000 times
  more penicillin than Fleming's original isolate

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Drawbacks - 1 Resistance

• Over-prescribing by physicians and veterinarians
  commonly occurs
• Antibiotics were incorporated into animal feed
  for use in feedlots
• Widespread use led to the evolution of
  penicillin-resistant bacteria

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Rise of Resistant Bacteria

• Bacteria reproduce every 20 min
• Time-table for the evolution of new strains
  faster than other organisms
• By the early 1960s resistance was evident among
  many types of bacteria
• By the early 1990s antibiotic resistance has
  become a major cause for concern among the
  medical community

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Drawback-2 Allergies

• Small percentage of population is allergic
• Can result in severe or even fatal anaphylactic
  reactions
• Penicillin is the most frequent cause of
  anaphylaxis
• Several hundred die each year from anaphylaxis
  due to penicillin allergy

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Synthesis of Penicillin

• Penicillin - one of a family of b-Lactam
  antibiotics
• b-Lactams produced by asexual fungi, some
  ascomycetes, and several actinomycete bacteria
• b-Lactams are synthesized from amino acids valine
  and cysteine

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b Lactam Basic Structure
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Penicillins

• When penicillin first isolated, it was found to
  be a mixture of various penicillins
• Different R groups attached to the molecule
• When large scale production began, it was found
  that by adding phenylacetic acid to the medium,
  the penicillin was all one type -penicillin-G

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Penicillin-G
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Penicillin-G

• Still an important antibiotic
• Disadvantage has been that it is unstable in acid
  conditions
• Given by injections - otherwise stomach acids
  would destroy

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Penicillin-V

• The addition of phenoxyacetic acid to the culture
  medium gives penicillin-V
• This is not as active as penicillin-G, but it is
  acid stable and can be given by mouth
• There are many other naturally occurring
  penicillins but these are still clinically very
  important

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Penicillin-V
phenoxy methyl penicillin
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Semi-Synthetic Penicillins

• A strain of Penicillium chrysogenum found that
  produced large amounts of 6-amino penicillanic
  acid (6-APA)
• 6-APA lacked antibiotic activity but it could be
  used to add a variety of side chains and create
  semi-synthetic penicillins
• methicillin and ampicillin
• Semi-synthetics have made penicillins a versatile
  group of antibiotics

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RH
6-APA
Ampicillin
Methycillin
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Mode of Action

• b-lactam antibiotics inhibit formation of the
  bacterial cell wall by blocking cross-linking of
  the cell wall structure
• Bind to PBP penicillin binding proteins in cell
  membrane that function as transpeptidases
• Inhibit transpeptidases, which catalyze the final
  cross linking step in the synthesis of the
  peptidoglycan cell wall
• Result is bacterial wall is weakened and cell
  explodes from osmotic pressure

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b-Lactamase

• Within a decade of the introduction of
  penicillin, resistance was starting to develop
• Resistance due to the presence of an enzyme that
  cleaved the b-lactam ring - enzyme called
  b-lactamase
• By late 1950s looked like penicillin would dimish
  in importance

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b-Lactamase
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Cephalosporin

• In 1948 Giuseppe Brotzu, an Italian
  microbiologist identified a compound produced by
  Cephalosporium acremonium that was an effective
  treatment for gram-positive infections as well as
  some gram-negative ones such as typhoid.
• Brotzu sent a culture of this fungus to Florey.
  The team at Oxford once again isolated the active
  compound which they named cephalosporin.

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Cephalosporin Group

• Since its initial isolation, a whole group of
  cephalosporins have been manufactured.
• Broader spectrum than penicillins
• Effective against many penicillin-resistant
  strains of bacteria.
• Much more expensive to produce many of the newer
  cephalosporins are reserved for hospital use.

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Cephalosporin
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Clinically Important Antibiotics
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Anti-Fungal Compounds

• Antibiotics (per se) do not work on eukaryotic
  organisms or viruses
• Need to control one eukaryote within the tissues
  of another eukaryote
• There are several anti-fungal drugs that are
  widely used today but frequent side effects
• The increase in fungal infections and the rise in
  antifungal drug resistance has led to the need
  for new drugs