MICROBIOLOGY

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MICROBIOLOGY ALCAMO

• LECTURE
• Chemotherapeutic Agents and Antibiotics

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Chemotherapeutic Agents and Antibiotics

• For centuries, doctors thought that drastic
  measures were necessary to save a patient from
  infectious disease
• Purges and bloodlettings
• Large doses of chemicals
• Ice water baths
• Starvation
• These treatments probably made a bad situation
  worse

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Chemotherapeutic Agents and Antibiotics

• In 1825, doctors in Boston and London wanted to
  see what would happen if these treatments were
  not given
• They found that no treatment at all was better
• For the next 60 years it became the doctors job
  to diagnose disease, explain it to the family,
  and sit by caring for the patient

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Chemotherapeutic Agents and Antibiotics

• Late 1800s germ
• theory of disease
• Doctors understood
• where disease comes
• from but could do little
• Tuberculosis killed 1 of every 7 people that died
• Streptococcal heart valve disease, pneumonia, and
  meningitis killed many

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Chemotherapeutic Agents and Antibiotics

• 1940s chemotherapeutic agents and antibiotics
  were discovered
• Doctors learned that they could kill bacteria in
  the body without harming the body itself
• Doctors were altering the course of disease which
  made a dramatic change in the world

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Chemotherapeutic Agents Antibiotics

• Must be more harmful to MO than host cells
• Chemotherapy only helps the immune system to
  control the infection
• The immune system ultimately stops MOs

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Chemotherapeutic Agents

• Produced in lab, inorganic chemicals
• Sulfur, Arsenic, Quinine, Nicotinic Acid
• Still major medical applications
• Can be quite toxic to patient

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Antibiotics

• Originally Chemical produced by an MO which
  inhibits growth of other MOs
• Now synthesized in labs, Organic Chem

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Chemotherapeutic Agents Antibiotics

• Have anti-metabolite mechanisms
• Select for specific MO according to which life
  process you need to disrupt
• Protein synthesis
• Cell Wall structure
• Cell membrane structure
• RNA or DNA synthesis
• Chemical reactions

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History of Chemotherapy

• Paul Ehrlich worked with stains
• and dyes and found out they had antimicrobial
  properties
• Collaborated with Sahachiro Hata
• to produce Salvarsan 1st chemotherapeutic
  drug (cured syphilis)
• Problems
• Local reaction at injection site
• Church wanted syphilis to be a deterrent to
  immoral behavior

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History of Chemotherapy

• For the next 20 years, German scientists kept
  testing dyes for antimicrobial properties
• Gerhard Domagk tested prontosil dye on his own
  daughter when she became ill with septicemia and
  she recovered

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Sulfa Drugs

• It was determined that the
• active ingredient in prontosil
• is sulfanilimide
• In 1940, D.D. Woods and E.M. Fildes proposed a
  mechanism of action for sulfa drugs
• It showed how they could interfere with bacterial
  metabolism without damaging host tissues

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Competitive Inhibition

• Bacteria need folic acid to produce nucleic acids
  (DNA and RNA)
• Bacteria have an enzyme to make folic acid they
  cant get folic acid from environment like we do
• This enzyme joins PABA with 2 other components to
  make folic acid
• Sulfanilimide looks like PABA and enzyme will
  bind to it instead of PABA

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Sulfa Drugs

• Bactrim
• Sulfamethoxazole
• Used for urinary tract infections and pneumonia
• Gantrisin
• Sulfisoxazole
• Used for vaginal infections, conjunctivitis and
  toxoplasmosis

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Antibiotics

• Word means against life
• Chemical products or derivatives of certain
  organisms that are inhibitory to other organisms
• How did organisms gain the
• ability to produce antibiotics?
• Random genetic mutation
• Evolutionary advantage

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Antibiotics

• Mainstay for help with bacterial infections.
  Used for some fungal and protozoal
  infectionsUseless on viruses (2ndary Bact Inf)
• Usually safe/effective, some patients dangerously
  hypersensitive

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Alexander Fleming

• Discovered antibiotics
• One of his agar plates
• containing staphylococci
• became contaminated with a green mold
• He noticed the staphylococci didnt grow near the
  mold
• He identified the mold as a species of
  Penicillium and he named its substance penicillin

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Zone of Inhibition
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Penicillin

• Isolated from a fungus - Penicillium
• First antibiotic, 1940s
• Interferes with cell wall synthesis
• Effective against G MOsFew G- with massive
  doses
• Cillins a very large family of drugs

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This bacterium is lysing because an antibiotic
disrupted its cell wall. Why doesnt the
antibiotic lyse human cells?
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Disadvantages of Penicillin

• 1. Anaphylaxis or allergy
• Swelling of the eyes or wrists
• Flushed or itchy skin, hives
• Shortness of breath
• 2. Penicillin-resistant bacteria
• Produce penicillinase, an enzyme that converts
  penicillin into a useless compound
• Use too many antibiotics natural selection of
  antibiotic resistant bacteria

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Semi-synthetic Penicillins

• In the 1950s the beta-lactam nucleus of the
  penicillin molecule was identified and
  synthesized
• New penicillins were
• created by attaching
• different groups
• to this nucleus
• Ampicillin
• Amoxicillin

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Cephalosporin

• Isolated from a fungus - Cephalosporium
• Interferes with cell wall synthesis
• Similar to Penicillin can be used in allergic
  persons and with resistant MOs
• Interferes with some
• G and some G- MOs

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Streptomycin

• Isolated from a filamentous (mold-like) soil
  bacteria - Streptomyces
• Attaches to ribosomes, blocks messenger RNA
• Carefully used, toxic side effects (deafness)
• Mycins a very large family of drugs
• Neosporin contains
• Neomycin

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Chloramphenicol

• Streptomyces 2nd family of drugsOriginal Prod
  Chloromycetin
• 1st Broad Spectrum AntibioticWide variety of
  G and G- MOs
• Interferes with protein
• synthesis, ribosomes
• blocked from mRNA

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Tetracycline

• Broad spectrum antibiotics
• Can be taken orally and were used widely in the
  1950s and 1960s
• Overused, so normal flora was eliminated from the
  intestines
• Then fungi (Candida albicans) flourished and
  antifungal antibiotics had to be taken
• Also caused gray-brown tooth discoloration

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Antimicrobial Drugs

• Chemotherapy The use of drugs to treat a disease
• Antimicrobial drugs Interfere with the growth of
  microbes within a host
• Antibiotic A substance produced by a microbe
  that, in small amounts, inhibits another microbe
• Selective toxicity A drug that kills harmful
  microbes without damaging the host

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The Action of Antimicrobial Drugs

• Bactericidal
• Kill microbes directly
• Bacteriostatic
• Prevent microbes from growing

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Antibiotic Assays

• 1. Tube dilution method determines the smallest
  amount of antibiotic necessary to inhibit a test
  organism
• Prepare a set of tubes with different
  concentrations of an antibiotic
• The tubes are inoculated with the test organism,
  incubated and examined for growth
• Extent of growth gets lower with increasing
  concentration of antibiotic
• When growth fails to occur you have reached the
  minimum inhibitory concentration (MIC)

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Antibiotic Assays

• 2. Agar or disk diffusion method operates on
  the principle that antibiotics will diffuse from
  a paper disk into agar medium containing test
  organisms
• Inhibition is observed as a failure of an
  organism to grow in the region of the antibiotic

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Kirby-Bauer Test

• 1. Pour agar into plate and inoculate with test
  organism
• 2. Apply paper disks containing known
  concentrations of antibiotics to the surface
• 3. Incubate plate
• 4. Compare diameters of zones of inhibition to a
  standard table to determine if test organism is
  susceptible
• If organism is susceptible, it will be killed
  in patients blood stream if experimental
  concentration of antibiotic is reached

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The Disk-Diffusion Method
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Antibiotic Resistance and Abuse

• During past 25 years, a large
• of bacterial species have evolved with
  resistance to drugs and antibiotics
• Resistant organisms are responsible for human
  diseases in
• Intestines, lungs, skin, urinary tract
• Common diseases that used to be easy to treat
  with a single dose of antibiotics are now hard to
  treat
• Bacterial pneumonia, strep throat, gonorrhea

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Antibiotic Resistance and Abuse

• How do MOs acquire resistance?
• Production of enzymes capable of destroying
  antibiotic (penicillinase)
• Changes in permeability of cell wall
• Resistance to drugs activity by bypassing a
  normal metabolic pathway and creating an altered
  one (new way to produce folic acid)

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Antibiotic Resistance and Abuse

• Antibiotic resistance
• may develop
• Normally - mutation
• From doctors prescribing too many antibiotics
  forced evolution
• From hospitals using too high doses of
  post-surgery antibiotics forced evolution
• From livestock feeds which contain 40 of all
  antibiotics produced in U.S. forced evolution

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Antibiotic Resistance and Abuse

• Can resistance be transferred??
• Researchers have transferred antibiotic
  resistance genes from one bacterial species to
  another using plasmids
• There is potential for the transfer of antibiotic
  resistance from a harmless bacterium to a
  pathogenic bacterium
• Result disease and death

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Antibiotic Resistance and Abuse

• Antibiotics have been known as miracle drugs
  they are overworked miracles
• Suggestions have been made to control their use
  as strictly as narcotics are controlled
• But, antibiotics are abused in 3rd world
  countries where they are sold over-the-counter

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