1. Control of Pathogenic Bacteria

2. Bacteria spread in various ways:
1. moisture droplets in the air
2. dust
3. direct contact
4. fecal contamination
5. animal bites
6. wounds

3. Aseptic Techniques To prevent infection we use:
(In addition to body’s own defence mechanisms ...)
To prevent infection we use:
autoclaves: sterilization of surgical equipment by extreme heat
protective clothing: masks, gowns, gloves
antiseptics: chemicals that kill bacteria (ex: alcohol, Lysol, etc)
air filtration: in operating rooms
extermination: kill animals that
are carrying the disease
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4. Treatment of Active Infections (kill bacteria inside host)
problem: You need to find a medication that kills
bacteria, but won’t kill the host cells.
solution: antibiotics
most important discovery of the last century
attack bacterial cell walls causing bacteria to die
not dangerous to humans or other animals
animal cells have no cell walls
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5. Discovery of Penicillin
discovered by Alexander Fleming (1929)
he cultured bacteria on agar
mould contaminated his plates
aspergillus penicillium
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6. Discovery of Penicillin
petri dish with nutrient agar
bacterial colonies growing on agar
mould colony
zone of inhibition (no growth)
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7. Discovery of Penicillin
he observed a zone of inhibition:
(no bacterial growth) around the mould colony
conclusion: mould produces a chemical (antibiotic) that kills bacteria
i.e. He discovered penicillin.
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8. Antibiotics
since the discovery of penicillin, many antibiotics have been discovered
some ( > 2500) produced naturally by microorganisms
others synthetically
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9. Antibiotics researchers must continue to find new antibiotics because:
different species of bacteria have different cell walls, therefore need different antibiotics to destroy them
bacteria evolve very quickly - mutate
if only one bacterium becomes resistant…..
they reproduce asexually (binary fission) so quickly
(~ every 20 minutes - 7h → 1x106 bacteria)
can pass on antibiotic resistance to other
species through sexual reproduction
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10. Antibiotic Resistance
Antibiotic resistance develops from
genetic variations within a bacterial population
After first exposure to an antibiotic:
Weaker strains of bacteria are killed
Stronger antibiotic resistant strains survive and pass their resistance to the next generation
FROM WHAT WE KNOW WHY SHOULD YOU ALWAYS TAKE ANTIBIOTICS FOR THE FULL LENGTH OF TIME?
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11. Homework
Page 127 # 1, 2, 4, 7
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