Download What is an antibiotic?

Prokaryotic Diversity and
Molecular Genetics
Biol 103 Diversity of Life
Scott Samuels
• Office: Science Complex 207
• Phone: 243-6145
• Email: [email protected]
• Office hours:
Monday, Tuesday, Wednesday
2:10 pm–3:00 pm
My research interests:
• DNA supercoiling
(and higher-order structure)
•DNA topoisomerases (gyrase)
• Regulation of transcription
• Mechanism of replication
(linear DNA in bacteria)
• Antibiotic resistance
My favorite system:
Borrelia burgdorferi
-causative agent of Lyme disease
Theme: Prokaryotic Diversity
and Molecular Genetics
1. Antibiotic resistance
2. Prokaryotic diversity
3. DNA structure and function
4. DNA replication
5. Bacterial genetics
6. Gene expression
7. The lac operon
8. Seminar: Lyme disease gene regulation
Antibiotic Resistance
I. Antibiotics
A. Definition
B. Mechanisms of action (targets)
C. Disease treatment
II. Resistance
Reading (1)
The challenge of antibiotic resistance, Levy,
Scientific American, March 1998 (Web)
What is an antibiotic?
Antibiotics
• Organic substances that are either toxic or
growth-inhibitory for organisms
• Infectious disease therapy depends on
selective toxicity
• Target is a structure (or function) only found
in specific organism
Focus on antibiotics that target bacteria
Targets of antibacterial agents
• Penicillins,
bacitracin, and
vancomycin
• Aminogylcosides,
tetracyclines, and
erythromycin
• Rifamycins
• Fluoroquinolones
and coumarins
Cell wall synthesis
Protein synthesis
(ribosomes)
RNA synthesis
DNA synthesis (gyrase)
Treatment of bacterial diseases
• Strep throat (Streptococcus pyogenes)
• Pneumonia/ear infections (S. pneumoniae)
• Gonorrhea (Neisseria gonorrhoeae)
• Lyme disease (Borrelia burgdorferi)
• RMSF (Rickettsia rickettsii)
• Tuberculosis (Mycobacterium tuberculosis)
…and many others….
Antibiotic Resistance
I. Antibiotics
II. Resistance
A. Mechanisms
B. Acquisition/Evolution
C. Factors
D. Preventative actions
How do disease-causing bacteria become
resistant to antibiotics?
What mechanisms do bacteria use to
become resistant to antibiotics?
Mechanisms of
antibiotic resistance
• Keep antibiotic out of cell
• Pump antibiotic out of cell
• Inactivate antibiotic
–destroy
–modify
• Change target
How do bacteria acquire these mechanisms
of antibiotic resistance?
Acquiring resistance
• Obtain genetic element from others
Plasmid/gene uptake (transformation)
Virus (transduction)
Sex (conjugation)
• Mutate (change DNA sequence)
Overproduction of target
Alteration of target
Loss of target
Evolution of genetic elements
that encode resistance
• Found in a remote community in Borneo
that had never been exposed to antibiotics
• Survival mechanism in presence of
antibiotics produced by other organisms in
soil or bowel
(Davis et al., 1970)
Factors that contribute to
antibiotic resistance
• Overuse of antibiotics
–meat and dairy production
• Inappropriate use of antibiotics
–no effect on viral diseases
• Incomplete use of antibiotics
–not finishing prescription
Antibiotic resistance as a
public health problem
•
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•
•
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Methicillin-resistant Staphylococcus aureus
Vancomycin-resistant enterococci
Penicillin-resistant pneumococci
Drug-resistant gonorrhea
Multidrug-resistant tuberculosis
Antibiotic residues in milk
• The existing antibiotic testing program
cannot guarantee that illegal residues are
not present in the milk supply
(GAO, 1990, 1992)
• Even FDA “safe levels” (from 10 to 150
parts per billion) of antibiotic residues can
select for antibiotic resistance in S. aureus
(Brady et al., 1993)
Actions you can take to limit the
development of
antibiotic resistance
• Do not demand antibiotics from your
physician.
• When given antibiotics, take them exactly
as prescribed and complete the full course
of treatment; do not hoard pills for later use
or share leftover antibiotics.
Your mother was right:
• Wash fruits and vegetables thoroughly;
avoid raw eggs and undercooked meat,
especially in ground form. (The majority of
food items that cause diseases are raw or
undercooked foods of animal origin such as
meat, milk, eggs, cheese, fish or shellfish.)
• Use soaps and other products with
antibacterial chemicals only when
protecting a sick person whose defenses are
weakened.
Alliance for the Prudent Use of Antibiotics
Summary
• Antibiotics are “miracle drugs”
• Antibiotic resistance:
“the new apocalypse”
• Wash hands and use antibiotics prudently
Reading (2)
Chapter 27
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