Download Micro unit 12B Notes - Nutley Public Schools

MICROBIOLOGY – ALCAMO
LECTURE:
Chemotherapeutic Agents
and
Antibiotics
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
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
doctor’s job to diagnose disease,
explain it to the family, and sit by
caring for the patient
Chemotherapeutic Agents
and Antibiotics
• Late 1800’s – 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
Chemotherapeutic Agents
and Antibiotics
• 1940’s – chemotherapeutic agents and
antibiotics were discovered
• Doctor’s 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
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
Chemotherapeutic Agents
•
•
•
•
Produced in lab, inorganic chemicals
Sulfur, Arsenic, Quinine, Nicotinic Acid
Still major medical applications
Can be quite toxic to patient
Antibiotics
• Originally: Chemical produced by an MO
which inhibits growth of other MOs
• Now synthesized in labs, Organic Chem
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
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
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
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
Competitive Inhibition
• Bacteria need folic acid to produce
nucleic acids (DNA and RNA)
• Bacteria have an enzyme to make folic
acid – they can’t 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
Sulfa Drugs
• Bactrim:
– Sulfamethoxazole
– Used for urinary tract infections and
pneumonia
• Gantrisin:
– Sulfisoxazole
– Used for vaginal infections, conjunctivitis
and toxoplasmosis
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
Antibiotics
• Mainstay for help with bacterial
infections. Used for some fungal and
protozoal infections
Useless on viruses (2ndary Bact Inf)
• Usually safe/effective, some patients
dangerously hypersensitive
Alexander Fleming
• Discovered antibiotics
• One of his agar plates
containing staphylococci
became contaminated with a green
mold
• He noticed the staphylococci didn’t
grow near the mold
• He identified the mold as a species of
Penicillium and he named its substance
penicillin
Zone of Inhibition
Penicillin
• Isolated from a fungus - Penicillium
• First antibiotic, 1940’s
• Interferes with cell wall
synthesis
• Effective against G+ MOs
Few G- with massive doses
• “Cillins: a very large family
of drugs
This bacterium is
lysing because an
antibiotic disrupted
its cell wall. Why
doesn’t the
antibiotic lyse
human cells?
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
Semi-synthetic Penicillins
• In the 1950’s 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
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
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
Chloramphenicol
• Streptomyces’ 2nd family of drugs:
Original Prod: Chloromycetin
• 1st “Broad Spectrum” Antibiotic
Wide variety of G+
and G- MOs
• Interferes with protein
synthesis, ribosomes
blocked from mRNA
Tetracycline
• Broad spectrum antibiotics
• Can be taken orally and were used
widely in the 1950’s and 1960’s
• 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
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
The Action of Antimicrobial
Drugs
• Bactericidal
– Kill microbes directly
• Bacteriostatic
– Prevent microbes from growing
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)
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
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
patient’s blood stream if experimental
concentration of antibiotic is reached
The Disk-Diffusion Method
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
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 drug’s activity by bypassing
a normal metabolic pathway and creating
an altered one (new way to produce folic
acid)
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
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
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-thecounter