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Humans and the Microbial WorldChapter 1

Current Microbial ThreatsMeasles (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

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

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

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

Vital activities of microorganisms

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

Applications of 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

Medical microbiology

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

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

Medical microbiology (cont.)

Agent Host Disease

Ebola virus Bats Ebola hemorrhagic fever

SARS virus Bats Severe acute respiratory syndrome

Sin Nombre virus Deer mouse Hantavirus cardiopulmonary syndrome

Nipah virus Bats Nipah encephalitis

Dengue virus Mosquitos Dengue fever; Dengue hemorrhagic fever

Machupo virus Vesper mouse Bolivian hemorrhagic fever

Avian influenza viruses

Various birds Influenza

Some recently discovered agents and their animal hosts

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.)

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

1.4 Viruses, Viroids, and PrionsViruses

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

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”)