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Humans and the Microbial
World
Chapter 1
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
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
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
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
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
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
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
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 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
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”)