Transcript Antibiotic Resistance

Antibiotic Resistance
Why Evolution is Important Now
What are Antibiotics?
• Chemicals that either kill or inhibit the growth of
bacteria
• Naturally produced by bacteria and fungi
Erythromycin – produced by bacteria Streptomyces erythraeus
Penicillin – produced by fungi Penicillium
• Can be also artificially produced in the laboratory
Sulfanilamide, Cipro – completely synthetic
Ampicillin, Amoxycillin – natural products with chemical modification.
How Antibiotics Work
Prevent proper formation of the bacterial cell wall
Cell wall normally prevents cell from bursting when excess water
enters the cell – if cell wall is damaged, cell bursts and dies
Examples are penicillin, ampicillin, amoxycillin, vancomycin
Disrupt protein synthesis or cell metabolism
-Bind to ribosomes - disrupt process in various ways
Examples are tetracycline, erythromycin, streptomycin, kanamycin
-Block synthesis of needed metabolic chemicals – e.g. folic acid
Example is sulfanilamide
Interfere with DNA synthesis
Block replication of the bacterial chromosome
Example is Cipro
What Is Antibiotic Resistance?
Antibiotic Resistance is when bacteria
possess the ability to deactivate the
action of antibiotics.
What are the Mechanisms of
Antibiotic Resistance?
• Bacteria possess structures that prevent antibiotic
from entering the cell (modify cell wall).
• Bacteria can pump antibiotic back out of the cell
through their plasma membrane.
• Bacteria can destroy the antibiotic once inside the
cell.
• Bacteria can bind other substances to the antibiotic
once inside the cell in order to inactivate its action.
How is Antibiotic Resistance
Acquired?
MOST BACTERIA DO NOT NATURALLY
POSSESS RESISTANCE TO ANTIBIOTICS!!
(Other than their own that they produce – for
example - Streptomycetes are resistant to
Streptomycin)
Antibiotic Resistance is Acquired
Through:
• Natural mutation
• Exchange of genes
through:
Conjugation
Transduction
Transformation
Conjugation
Bacteria connect to
each other using a
thread-like structure
called a pilus. A
section of DNA –
often a circular piece
of DNA called a
plasmid is transferred
from one bacterium to
the other.
Illustrations from Doc Kaiser’s Microbiology Home Page
http://student.ccbc.cc.md.us/courses/bio141/lecguide/unit4/g
enetics/recombination/
Transduction
A virus can take up a piece of
DNA from its bacterial host and
insert it into its own viral
genome. It then takes over the
bacterial cell host and
replicates many copies of the
virus. The bacterial cell is
ruptured and the replicated
viruses erupt from the infected
cell. When one of the viruses
infects a new cell, it inserts the
original bacterial DNA into the
new cell, where the stolen
piece becomes integrated into
the new cell's DNA.
Illustrations from Doc Kaiser’s Microbiology Home Page
http://student.ccbc.cc.md.us/courses/bio141/lecguide/un
it4/genetics/recombination/
Transformation
DNA from dead
bacteria is
taken in and
incorporated
into the genome
of living
bacteria
Illustrations from Doc Kaiser’s Microbiology Home Page
http://student.ccbc.cc.md.us/courses/bio141/lecguide/unit4/genetics/recombinat
ion/
So What’s the Big Deal if One
or Two Bacteria Have Antibiotic
Resistance?
• If the antibiotic resistance offers a
competitive advantage to the bacteria, other
bacteria will die off, and the resistant bacteria
will thrive.
• Within that particular environment, rapid
resistant bacterial reproduction would lead to
the development of a resistant strain that could
cause harm to humans and other living things.