1. Lab 9: Antibiotic Resistance and The
Susceptibility of Bacteria Lab
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2. After successfully participating in
this lab, you will be able to:
• Distinguish between antiseptics, disinfectants,
antibiotics, and sanitizers.
• Describe the effects of antimicrobials and antibiotics on
bacteria.
• Differentiate between sterilizing and disinfecting
• Differentiate between pathogenic bacteria and
probiotics.
• Describe the effects of antibiotic resistance and MRSA
on humans.
• Understand evolution as the underlying theme in
bacterial change.
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3. • In 1928 while working
with Staphylococcus
bacteria, Scottish scientist
Alexander Fleming
noticed that a type of
mold growing by accident
on a laboratory plate was
protected from, and even
repelled, the bacteria.
• The active substance,
which Fleming called
penicillin, was literally an
antibiotic—it killed living
bacteria.
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4. • Thus began the age of using natural and, later,
synthetic drugs to treat people with bacterial
infections.
• Though not widely popular until the 1940s,
antibiotics and other antimicrobials (medicines
that kill or slow growth of a microbe) have saved
countless lives and blunted serious complications
of many feared diseases and infections.
• The success of antimicrobials against disease-causing
microbes is among modern medicine's
great achievements.
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5. Bacteria are everywhere
• There are five million, trillion, trillion bacteria
on Earth – 5 with 30 zeroes after it.
• Only 1 percent of bacteria are inside living
things
• Most bacteria are found in soil or in the
oceans, but some have been found 40 miles
up in the atmosphere.
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6. Are All Bacteria Bad?
• No – without the bacteria in your gut, you
couldn’t survive.
• Probiotics – helpful bacteria that help you digest
your foods (yogurt)
• Things that kill your healthy gut bacteria – Birth
control pills, antibiotics, alcohol, smoking, stress,
poor diet.
• Without these healthy bacteria, you see
symptoms such as bloating, constipation,
diarrhea, allergies, skin conditions.
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7. The Problem
• After more than 70 years of widespread
use, evolution of disease-causing
microbes has resulted in many
antimicrobials losing their effectiveness.
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8. • Evolution through
natural selection
can occur
remarkably quickly
when selection
pressures are very
strong and
reproductive rates
are very fast
(some bacteria
generations are as
short as 15-20
minutes)
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9. • As microbes evolve, they
adapt to their environment.
If something stops them
from growing and
spreading—such as an
antimicrobial— they evolve
new mechanisms to resist
the antimicrobials by
changing their genetic
structure. Changing the
genetic structure ensures
that the offspring of the
resistant microbes are also
resistant.
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10. • Penicillin was
extensively used
in Hungary in the
early 1970's.
• By 1976,
more than 50%
of the strains of
Streptococcus
pneumoniae were
resistant to
penicillin.
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11. Dangers of Antibiotic Resistance
• Antibiotic resistance is one of the world's most pressing
public health problems.
• This condition occurs when bacteria change in some way
that reduces or eliminates the effectiveness of drugs,
chemicals, or other agents designed to cure or prevent
infections.
• Widespread overuse of antibiotics is fueling an increase in
antibiotic-resistant bacteria.
• So the next time you really need an antibiotic for a
bacterial infection, it may not work.
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12. If You Have a Cold or Flu, Antibiotics
Won't Work for You!
• Colds and flu are caused by
viruses, not bacteria. Taking
antibiotics when you have a
virus may do more harm than
good. Get smart about when
antibiotics are appropriate.
Taking them for viral infections,
such as a cold, cough, the flu, or
acute bronchitis:
• Will not cure the infection;
• Will not keep other people
from getting sick;
• Will not help you feel better;
and
• May cause unnecessary and
harmful side effects.
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13. MRSA
• MRSA stands for Methicillin-resistant Staphylococcus
aureus. This type of bacteria causes “staph” infections
that are resistant to treatment with usual antibiotics.
• MRSA occurs most frequently among patients who
undergo invasive medical procedures or who have
weakened immune systems and are being treated in
hospitals and healthcare facilities such as nursing
homes and dialysis centers.
• MRSA in healthcare settings commonly causes serious
and potentially life threatening infections, such as
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15. Coevolution
• An interactive evolutionary relationship
between two or more species in which direct
genetic change in one species is attributable
to genetic change in the other(s).
• Antibiotics are now everywhere in the
environment, and humans and bacteria are
engaged in coevolution. Who is likely to win?
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16. Quick Facts
• Many infectious
diseases are increasingly
difficult to treat because of
antimicrobial-resistant
organisms, including
staphylococcal infection,
tuberculosis, gonorrhea,
candida infection.
• Between 5 and 10 percent
of all hospital patients
develop an infection,
leading to an increase of
about $5 billion in annual
U.S. healthcare costs.
• About 90,000 of these
patients die each year as a
result of their infection, up
from 13,300 patient deaths
in 1992.
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17. Why are we doing the lab today?
• Given a bacterial culture, students will
demonstrate aseptic technique.
• Identify household disinfectants and
antiseptics and distinguish between the two.
• Explain the consequences of antibiotic
resistance.
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