Download Antibiotic Resistance: How and So What?

Antibiotic Resistance:
How it happens and why all
the fuss?
(in your packet)
• Bacteria have been around for
___?___ billion years
Bacteria are
Everywhere!
Bacteria are Everywhere!
Skin: about a trillion bacteria
Alimentary canal (mouth, throat, stomach, intestines): tens of
trillions of bacteria!
Nose, eyes, toes . . .
Bacteria comprise about
1/20th of your total body
weight!
What is a bacterium?
Cell
membrane
Cell wall or
envelope
Bacterial
chromosome
(DNA)
Plasmid DNA
- small
circles of
DNA that
contain a few
genes
Human cell
nucleus
chromosomes
E.coli bacterium
Flu virus
.
10 micrometers
= 1/100th of a millimeter
Bacterial Replication
Bacteria can double in less than twenty
minutes under optimal conditions!
Bacteria can double in less than twenty
minutes under optimal conditions!
Bacteria can double in less than twenty
minutes under optimal conditions!
Bacteria can double in less than twenty
minutes under optimal conditions!
Bacteria can double in less than twenty
mintues under optimal conditions!
“Good” bacteria
• Form defensive
barrier
– Skin, intestines
• Aid digestion
• Produce vitamin K
• Clear away debris
- E. Coli
- Lactobacillus
Pathogenic (disease-causing)
bacteria
Streptococcus
pneumoniae pneumonia
Streptococcus
pyogenes strep throat
Helicobacter pylori Stomach ulcers
Haemophilus
influenzae meningitis
Staphylococcus
aureus wound infections
How antibiotics work
• Antibiotics are chemicals that disrupt
bacterial processes
Stop protein
Stop cell wall
building: cell dies
construction: cell
bursts
Stop copying DNA:
cells can’t divide
What is Antibiotic
Resistance?
• Resistant bacteria no longer killed in
presence of specific antibiotic.
Antibiotic X
Antibiotic X
All killed
Antibiotic Y
All killed
How do bacteria become
resistant?
Spontaneous mutation of DNA
• Many different random
mutations are present in a
population of bacteria.
• Some “lucky” mutations may
provide an advantage,
especially if the environment
changes.
How Else?
Acquire resistance genes from other bacteria
How can the bacteria become
resistant?
• Spontaneous
mutations
• They transfer DNA in
a plasmid
Mechanisms of Resistance
Resistant Bacteria Can:
1. Modify or destroy
the antibiotic.
2. Force out antibiotic.
3. Alter the target.
Essential
Bacterial
Protein
Essential
Bacterial
Protein
“Superbugs”
Uptake of
plasmid:
over 12,000
in Guatemala
died in 1968
of acute
diarrhea
Bacteria that are resistant to many antibiotics
Need for stronger, newer drugs
Antibiotic Resistance
Not immunity!!
In the absence of antibiotics, resistant
bacteria are less likely to survive.
Resistant strain cannot
compete with all other
bugs
With antibiotic, resistant bacteria rapidly take over.
So does this mean
antibiotics are evil?
Antibiotics are wonderful drugs when
administered and used properly!
• Penicillin on market in 1943 saved numerous lives in WWII!
• Ear infections in children
treatable.
• Lower incidence of infection in
surgical patients.
But there are problems!
• 4 years after introduction of
penicillin, resistance began to
develop.
• Needless exposure to antibiotics
selects for resistant strains.
Who can change?
• Doctors and Patients
• Livestock/Poultry Industry
• Antibacterial Home Products
Patients
and
• Take for prescribed
period of time.
• Don’t go to doctor
with expectation of
receiving prescription.
Doctors
• Only prescribe when
necessary.
• Narrow spectrum drugs.
Subtherapeutic Dosage
Problem
1/2
Dose
Highly susceptible
bacteria
Less susceptible
bacteria
Resistant bacteria
Full
Dose
Stop Taking
Antibiotic
Summary
• Bacteria become resistant through
mutations or by getting genes from other
bacteria.
• We should only use antibiotics when we
really need to.
• Overuse in agriculture and at home
encourages appearance of resistant bugs.
OCVSRS
• Overpopulation – lots of bacteria, not all can
survive
• Competition – for survival in the presence of
antibiotic
• Variety – Some bacteria are naturally resistant,
some are not
• Selection – The resistant ones are “selected for” and
survive the presence of the antibiotic
• Reproduction – The resistant ones are able to
reproduce more and pass the resistance gene to their
offspring, making it more common in the population
CDC Message about
antibiotic resistance
QuickTime™ and a
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Livestock/Poultry Industry
• Antibiotics given to
livestock, poultry, and even
to plants as a preventative
measure to promote growth.
• Link between this use and
people infected with
resistant strains.
Good News
• 1997 - Vancomycin banned from chicken
feed in Europe.
• July 2003 - McDonald’s vendors will no
longer treat animals with preventative
antibiotics.
• In Europe, animal health maintained
through improvements in living
conditions.
Antibacterials at Home
• Triclosan resistance
emerging.
• Triclosan contributes
to resistance of
other drugs.
From Dishwater to
Groundwater
• Triclosan very abundant in residential
streams.
How do bacteria become
resistant?
• Resistance arises from changes in the
bacterial genome.
– DNA -> RNA -> Protein
• These changes happen randomly
• These new proteins can help protect the
bacteria from the antibiotic.