Viruses and Bacteria: Infection and Disease

1. Biology Unit 8a – Viruses & Bacteria Chapter 18

2. Viruses

3. Infections can be caused in several ways • Viruses, bacteria, viroids, and prions can all cause infection. Any disease-causing agent is called a pathogen.

4. A virus is made of DNA or RNA and a protein coat. • non-living pathogen • can infect many organisms • A viroid is made only • of single-stranded • RNA. • causes disease in plants • passed through seeds or pollen

5. A prion is made only of proteins. • causes misfolding of other proteins • results in diseases of the brain

6. Viruses differ in shape and in ways of entering host cells. capsid surfaceproteins nucleic acid nucleic acid capsid Surface proteins lipidenvelope capsid nucleic acid surfaceproteins lipid envelope • Viruses have a simple structure. • genetic material • capsid, a protein shell • maybe a lipid envelope, a protective outer coat enveloped(influenza) polyhedral(foot-and-mouth disease) helical(rabies)

7. Bacteriophages infect bacteria capsid DNA tail sheath tail fiber

8. Viruses enter cells in various ways colored SEM; magnifications: large photo 25,000; inset 38,000x • bacteriophages pierce host cells. • Viruses of eukaryotes enter by endocytosis or by fusing with the membrane

9. Viruses cause two types of infections. host bacterium The bacterophage attachesand injects it DNA into a host bacterium. The host bacterium breaks apart, or lyses. Bacteriophages are able to infect new host cells. The viral DNA forms a circle. The viral DNA directs the hostcell to produce new viral parts.The parts assemble into newbacteriophages. • A lytic infection causes the host cell to burst.

10. The prophage may leave the host’s DNA and enter the lytic cycle. The viral DNA is called a prophage when it combines with the host cell’s DNA. Although the prophage is not active, it replicates along with the host cell’s DNA. Many cell divisions produce a colony of bacteria infected with prophage. • A lysogenic infection does no immediate harm.

11. Viruses cause many infectious diseases HIV-infected white blood cell • There are many examples of viral infections. • common cold • influenza • SARS • HIV The body has natural defenses against viruses

12. Vaccines are made from weakened pathogens • A vaccine stimulates the body’s own immune response. • Vaccines prepare the immune system for a future attack. • Vaccines are the only way to control the spread of viral disease.

13. Bacteria & Archaea

14. Bacteria and archaea are both single-celled prokaryotes. • Prokaryotes can be grouped by their need for oxygen. • obligate anaerobesare poisoned byoxygen • obligate aerobes need oxygen • facultative aerobes can live with or without oxygen

15. Bacteria commonly come in three forms Lactobacilli: rod-shaped Enterococci: spherical Spirochaeta: spiral • rod-shaped, called bacilli • spiral, called spirilla or spirochetes • spherical, called cocci Archaea have many shapes

16. Bacteria and archaea have similar structures pili plasmamembrance flagellum chromosome cell wall plasmid This diagram shows the typical structure of a prokaryote. Archaea and bacteria look very similar, although they have important molecular differences. • plasmid • flagellum • pili

17. GRAM NEGATIVE GRAM POSITIVE • The amount of peptidoglycan within the cell wall can differ between bacteria Archaea have different lipids entirely

18. Gram staining identifies bacteria Gram-negative bacteria have a thin layer of peptidoglycan and stain red. Gram-positive bacteria have a thicker peptidoglycan layer and stain purple. • gram-positive stains purple, more peptidoglycan • gram-negative stains pink, less peptidoglycan

19. Bacteria have various strategies for survival conjugation bridge TEM; magnification 6000x • Prokaryotes exchange genes during conjugation • Bacteria may survive by forming endospores (dormant alternate life forms) Clostridium botulinum - Gram-positive, endospore-forming, rod prokaryote. Vegetative and spore stages: note the flagella. Causes food poisoning (botulism), wound infections and infant botulism

20. Prokaryotes perform important functions for organisms and ecosystems • Prokaryotes live in digestive systems of animals. • make vitamins • break down food • fill niches • Bacteria help ferment many foods • yogurt, cheese • pickles, sauerkraut • soy sauce, vinegar Lactobacillus acidophilus

21. Prokaryotes have many functions in ecosystems • photosynthesize • recycle carbon, nitrogen, hydrogen, sulfur • fix nitrogen Nitrogen fixing bacteria • Bioremediation uses prokaryotes to break down pollutants • oil spills • biodegradable materials Bioremediation in soil

22. Some bacteria cause disease • Bacteria cause disease by invading tissues or making toxins. • A toxin is a poison released by an organism. Clostridium botulinum – food poisioning

23. Normally harmless bacteria can become destructive • may colonize new tissues Streptococcus bacteria on skin They are fairly harmless unless they come in contact with other tissue such as muscle or fat through an open wound.

24. Antibiotics are used to fight bacterial disease • Antibiotics may stop bacterial cell wall formation • Antibiotics do not work on • viruses. • Prevention is best method • to fight bacterial disease Penicillium chrysogenum

25. Bacteria are gaining resistance to antibiotics A bacterium carries genes for antibiotic resistance on a plasmid. A copy of the plasmid is transferred through conjugation. Resistance is quickly spread through many bacteria. • Through: • overuse • Using them too often and when not ill • underuse • Failure to take the entire course of medicine • misuse • Used in agriculture to increase rate of growth but bacteria already in the food becomes resistant.

26. The End That’s all until next week