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3. Humans and the Microbial World • Chapter 1

4. Current Microbial Threats • Measles (vaccine preventable) • Polio (vaccine preventable) • Whooping cough (pertussis; vaccine preventable) • Severe acute respiratory syndrome (SARS CoV) • Malaria • Yellow fever virus • West nile virus • Tuberculosis • Human immunodeficiency virus (HIV; AIDS) • Hepatitis C virus • Multidrug-resistant Staphylococcus aureus • H5N1 Avian Influenza • Nipah virus • Hospitals

5. 1.1 The World of Microorganisms • Spontaneous Generation: Life from nonliving materials • Disproved by Francesco Redi in late 1600s • Showed that worms which appeared on rotting meat were from fly eggs • Disproved again by Louis Pasteur in mid 1800s • Showed that appearance of microbes in sterilized media was from air-borne bacteria • Showed that sterilized materials remained sterile if kept isolated from the external environment

6. 1.2 Microbiology: A Human Perspective • Microorganisms cannot be seen without the aid of a microscope • There are more than 200,000 known microbes • Exist in virtually any environment that has water • Exhibit tremendous biodiversity • Compose the largest biomass group of living organisms

7. Vital activities of microorganisms • Nitrogen fixation: Converting atmospheric nitrogen (gas) to biomolecules (e.g., nucleic acids, amino acids) • Oxygen production: Convert carbon dioxide to molecular oxygen (O2) • Degradation of organic materials • Gastrointestinal tract • Sewage treatment plants

8. Applications of Microbiology • Food production: bread, beer • Bioremediation: decontamination of hazardous wastes • Useful products: ethanol fuel, antibiotics, amino acids • Genetic engineering: pharmaceuticals, vaccines • Genomics: genome sequencing permits understanding of disease mechanisms

9. Medical microbiology • Infectious diseases have killed more people than all wars and natural disasters combined • Outbreaks have changed the course of history • Notable pandemics • Spanish Flu (1918-1919): 50 million global deaths • Smallpox (middle ages): >100 millions deaths (est.) • Plague (1300s-1800s): >100 million deaths (est.) • Introduction of European diseases killed 30 to 40 million Native Americans (est.) • Vaccines have dramatically decreased the incidence of infectious diseases, especially in children

10. Medical microbiology (cont.) • Re-emergence of “Old” Infectious Diseases • Colorado has one of the lowest childhood vaccination rate in the U. S. • Cases of whooping cough have increased in the last few years • Many microbes have evolved antibiotic resistance

11. Medical microbiology (cont.) • Emerging infectious diseases • As humans encroach upon wild habitat, new infectious agents (microbes) are discovered • These agents are typically hosted by animals and are termed zoonotic agents Some recently discovered agents and their animal hosts

12. 1.3 The Microbial World • Bacteria • Procaryotes (no organelles) • Most have rigid cell walls composed of peptidoglycan • Archaea • Similar to bacteria, but no peptidoglycan • Often found in extreme environments (temperature, pH, high salt, etc.)

13. Eucarya • Complex organelles • Larger than bacteria and archaea • Members • Algae (photosynthesis) • Fungi (single and multicelluar) • Protozoa • Nomenclature • Genus is capitalized • Species is not • Both are italicized • Example: Yersina pestis

14. 1.4 Viruses, Viroids, and Prions • Viruses • Not considered living; they are complex macromolecules composed of nucleic acids and proteins (some have lipids) • Noninfectious viruses are said to be inactivated; you cannot “kill” a virus (since they are not considered living organisms) • Obligate intracellular parasites • Tend to be species-specific • Reside in a reservoir host in which they cause limited pathology or are chronic • Disease usually occurs when the virus “jumps” species • Deer mice permanently host Sin Nombre hantavirus without pathology (disease) • Humans infected with SNV often develop hantavirus cardiopulmonary syndrome

15. Viroids • Composed of RNA • Smaller than viruses • Rely on other viruses to replicate • Best characterized in plants • Prions • Composed of proteins only • Cause neurological disease, termed spongiform encephalopathy • Can be transmitted to humans from some animals (e.g. “mad cow”)