Lecture 1: The Microbial World
Edith Porter, M.D.
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Definition of Microbiology
Size dimensions
Classification of microbial agents
Microbial diversity
Role of microbes in nature
 Beneficial
▪ Environment
▪ Normal microbiota
▪ Commercial use and industrial applications
 Harmful
▪ Disease causing
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History of Microbiology
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Micro
 Small (micrometer range)
 Not visible with the unaided eye
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Bio
 Living
 Able to reproduce
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1 inch
1 cm
1 mm (1/10 of 1 cm)
1 mm (1/1000 of 1 mm)
Human Egg cell
(almost 1 mm)
Erythrocyte (7 mm)
Bacterium (2 –4 mm)
1 nm (1/1000 of 1 mm)
Large Virus (200 nm)
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Cellular organisms
 Eukaryotes (have a nucleus)
 Prokaryotes (do not have a nucleus)
Cell membrane
Nucleus with
genetic
material
Cell membrane
Genetic material
in cytoplasm
Nuclear membrane
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Acellular agents
 Viruses (nucleic acid + protein)
 Viroids (nucleic acid)
 Prions (protein)
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Prokaryotes
Domain
Bacteria
Domain
Archaea
Protozoa
Algae
Fungi
Slime
molds
Protists
Plants
Animals
Helminths
Domain
Eukarya
Eukaryotes
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Bacteria
 Peptidoglycan cell walls
 Binary fission
 For energy, use organic
chemicals, inorganic chemicals,
or photosynthesis
 Some produce molecular oxygen
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Archaea
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No peptidoglycan
Often in extreme environments
Diverse metabolic pathways
Not known to cause disease
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Cellulose cell walls
Use photosynthesis
for energy
Produce molecular
oxygen and organic
compounds
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Chitin cell walls
Use organic chemicals
for energy
 Two forms
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 Molds
▪ Multicellular
▪ Consisting of masses of
mycelia composed of
filaments called hyphae
 Yeasts
▪ Unicellular
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Dimorphic shift
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Unicellular
Absorb or ingest
organic chemicals
May be motile via
pseudopods, cilia,
or flagella
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Multicellular
animals
Parasitic
flatworms and
roundworms are
called helminths
Microscopic
stages in life
cycles
Dirofilaria immitis
Viruses are replicated
only when they are in a
living host cell
 Consist of DNA or RNA
core
 Core is surrounded by a
protein coat
 Coat may be enclosed in
a lipid envelope (from
host cell)
 Not all viruses are
harmful!
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Proteinaceous infectious
particles
 Consist of protein only
 Prions induce
conformation changes of
normal counter parts
 Body’s response leads to
symptomatic disease
 Neurodegenerative
disorders
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 CJD
 BSE
Brain section of animal with BSE
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Genus name followed by species name
Typically relate to the discoverer, habitat,
properties of the organism or its role
Genus name capitalized, species name lower
case
In italic (or underlined)
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Escherichia coli or E. coli
Discoverer
was Escherich
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lives in
colon
space
Neisseria meningitidis or N. meningitidis
Discoverer
was Neisser
causes
meningitis
space
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Plankton
Geochemical cycling
Microbes on human tongue
in a healthy individual
 Microbes recycle carbon,
nutrients, sulfur, and
phosphorus that can be used
by plants and animals
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Oxygen production
Normal flora: digestion,
vitamin production etc
 Cellulose digestion by
protozoa in termite gut
 Vitamin K production by
human intestinal flora
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A small percentage of all
microorganisms are
involved in diseases
Humans, animals and
plants can be affected
Opportunistic and obligate
pathogens
Diseases linked to
 microbial proliferation (e.g.
pus, pneumonia)
 toxic substances (e.g.
botulism, liver cancer)
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An organism that contains a nucleus
and a cell membrane is:
a.
b.
c.
d.
Virus
Prokaryote
Helminth
Archaea
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Choose the correct form of naming a
microbe:
a.
b.
c.
d.
Pseudomonas maltophilia
P. maltophilia
Pseudomonas m.
P. m.
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Development of tools to study microbes
Microbes exist
Microbes cause disease
Humans have a defense system
Drugs that kill microbes can be developed
Microbes can be exploited to the benefit of
humans
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For identification
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Optics (microscope)
Glass slides
Dyes
Culture media, inoculation material
Biochemical and molecular genetic assays
Advanced tools to study their role
 In vitro models
 Animal models
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~ 1600 Galilei: Lenses for use in
a microscope
1665: Robert Hooke described
cells
1676 Van Leeuwenhoek: first
recorded description of
microbes called “animacules”
17th/18th century: spontaneous
generation
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1858 Virchow proposes concept
of biogenesis
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Living things arise from non living
matter
Cells arise from living cells
1861 Pasteur disproves theory
of spontaneous generation (and
proves concept of biogenesis)
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Pasteur’s S-shaped flask kept microbes out but let air in
Fermentation, Pasteurization
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1847 Semmelweis
 childbed fever
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1867 Lister
 antiseptic surgery with phenol
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1876 Koch
 First proof that microbes cause
disease: Bacillus anthracis
causes anthrax
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1884 Gram stain developed,
Koch’s postulates
formulated
http://www.chemistryexplained.com/images/chfa_03_img0510.jpg
http://www.cdc.gov/ncidod/eid/vol7no2/images/cover_final_rgb.jpg
http://www.acponline.org/bioterro/anthrax/graphics/cutaneous.jpg
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Microbe must be present in every case of
disease and not in the healthy one.
Microbe must be isolated in pure culture.
When inoculated into a healthy tissue the
same disease must arise.
From this diseased tissue the same microbe
must be re-isolated in pure culture.
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1798 Jenner: cow pox
vaccination
 1884 Metchnikoff:
phagocytosis
 1890 Ehrlich: theory
of antibodies
 1921 Fleming:
lysozyme
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End of 19th century: dyes
1910 Ehrlich: First
chemotherapeuticum
(salvarsan: arsenic
compound to treat
syphilis)
 1928 Fleming: first
antibiotic (penicillin)
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 First successful treatment
in 1942
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Food preparation
(fermentation)
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Production of
Chemicals
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Bread, yogurt, kim-chi,
cheese, beer, wine and many
more
acetone, butanol, alcohol,
organic acids and many more
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Biotechnology
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Bioremediation
 Clean up of BP oil spill
Genetic engineering
 Recombinant drugs
Immunoassays
 Rebecca Lancefield:
serotyping of
Streptococcus spec.
Drugs
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Antibiotics, some cancer
drugs
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S. aureus
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Emerging infectious diseases and topics
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Biofilm
Avian Flue (H5N1) and swine flu
West Nile virus encephalitis
Mad cow diseases (prions)
E. coli O157:H7
Biofilm
▪ On teeth, mucosal surfaces, rocks, medical devices
▪ Hard to penetrate, source of recurrent infections
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Emerging antibiotic resistance
 Vancomycin resistant staphylococci and enterococci
 Multidrug resistant tuberculosis strains
 Resistance among malaria strains
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Microbial agents include prokaryotes,
eukaryotes and acellular agents
Prokaryotes are cells without nucleus
Bacteria, archaea, fungi, algae, and protozoa
are in the MICROMETER range (mm)
Viruses, acellular agents, are in the
NANOMETER range (nm)
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