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Transcript
Bacteria and Viruses
Section 3
Section 3: Bacteria, Viruses, and Humans
Bacteria and Viruses
Section 3
Key Ideas
• What are three important roles of bacteria and viruses?
• What are the steps described in Koch’s postulates?
• What are two ways that bacteria cause disease?
• How does antibiotic resistance develop?
• Why are viral diseases difficult to cure?
• What are four ways that a disease can emerge?
Bacteria and Viruses
Roles of Bacteria and Viruses
• Bacteria play vital roles
–
–
–
–
producing oxygen
making nitrogen available
decomposing organisms
symbiotic relationships.
• important in a variety of industries
–
–
–
–
–
food production
chemical production
Mining
environmental cleanup.
genetic research.
Section 3
Bacteria and Viruses
Section 3
Koch’s Postulates and Disease
Transmission
• German physician Robert Koch
– developed a technique for diagnosing the cause of an infection.
– known as Koch’s postulates.
• This technique is still used today to identify a diseasecausing agent, or pathogen.
Bacteria and Viruses
Section 3
Koch’s Postulates and Disease
Transmission, continued
• Step 1 The pathogen must be found in an animal with
the disease and not in a healthy animal.
• Step 2 The pathogen must be isolated from the sick
animal and grown in a laboratory culture.
• Step 3 When the isolated pathogen is injected into a
healthy animal, the animal must develop the disease.
• Step 4 The pathogen should be taken from the second
animal, grown in the lab, and shown to be the same as
the original pathogen.
Bacteria and Viruses
Section 3
Koch’s Postulates and Disease
Transmission, continued
• Diseases that can spread from person to person are
considered contagious.
• Can be spread
–
–
–
–
Directly
Through air
Water
Other objects
Bacteria and Viruses
Section 3
Bacterial Diseases
• Bacteria can cause disease by producing toxins
and by destroying body tissues.
• Toxins may be released or stored inside the
bacteria until the bacteria die.
• enzymes break down the host’s tissues into
nutrients that the bacteria can use.
Bacteria and Viruses
Bacterial Diseases
Section 3
Bacteria and Viruses
Section 3
Antibiotic Resistance
• Antibiotics are chemicals that inhibit the growth of or kill
microorganisms.
• Since the introduction of antibiotics, these drugs have
reduced illness, suffering, and deaths from bacterial
diseases.
Bacteria and Viruses
Section 3
Antibiotic Resistance, continued
Development of Resistance
• Antibiotic resistance is the ability of bacteria to tolerate
antibiotics.
• Mutations for antibiotic resistance arise naturally and
often in bacteria.
• Plasmids containing antibiotic-resistance genes can
pass between bacteria during conjugation.
Bacteria and Viruses
Antibiotic Resistance, continued
Development of Resistance
• Antibiotic kill vulnerable bacteria
• Resistant bacteria survive and reproduce.
• antibiotic-resistant bacteria become dominant
Section 3
Bacteria and Viruses
Section 3
Antibiotic Resistance, continued
Consequences of Resistance
• Diseases that were once easy to treat with antibiotics are
now more difficult to treat
• Widespread use of antibiotics promotes the spread of
antibiotic resistance. As bacteria become resistant,
physicians must switch to using different antibiotics.
• As new antibiotics are used, bacteria will probably
develop resistance to those as well.
Bacteria and Viruses
Section 3
Viral Diseases
• Viruses cause disease in bacteria, plants, and animals.
• Because viruses enter host cells to reproduce, it is
difficult to develop a drug that kills the virus without
harming the living host.
• Viruses can be transmitted by any action that brings
virus particles into contact with a host cell.
• Viruses have been shown to cause some types of
cancer.
Bacteria and Viruses
Section 3
Viral Diseases
• Symptoms of a viral illness can be caused by
several factors.
• Many symptoms of a viral infection, such as
aches and fever, result from the body’s response
to infection.
• A vaccine is a weakened form of a pathogen that
prepares the immune system to recognize and
destroy the pathogen.
Bacteria and Viruses
Viral Diseases
Section 3
Bacteria and Viruses
Visual Concept: AIDS (Acquired
Immunodeficiency Syndrome)
Section 3
Bacteria and Viruses
Section 3
Emerging Diseases
Emerging diseases are:
• diseases that are newly recognized
• diseases that have spread to new areas or to a new host
• diseases that have reemerged when a disease that was
once considered under control begins to spread
Bacteria and Viruses
Section 3
Emerging Diseases continued
• Diseases can spread to new areas or a new host when
people come into contact with a pathogen in a different
way than in the past.
• Environmental changes can cause diseases to emerge.
• Human behavior plays an important role in emerging
disease.