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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.
