Quinn
Chapter 1 - Microbiology, Microbial Pathogens and
Infectious Disease
● Founders of modern microbiology: Louis Pasteur and Robert
Koch
● Pasteur’s germ theory of disease → “germs” lead to disease
● Koch’s postulates → principles for proving that a specific
microorganism caused a particular disease
○ The pathogenic microorganism must be present in
every case of the disease but absent from healthy
animals
○ The suspected microorganism must be isolated and
grown in pure culture
○ The same disease must occur when the isolated
microorganism is injected into healthy susceptible
animals
○ The same microorganisms must be isolated again
from the injected animals which developed disease
● Dmitri Ivanovski → used Chamberland porcelain filters designed to remove bacteria
from drinking water
○ Transmitter tobacco mosaic disease from diseased to healthy plants
● Martinus Beijerinck → Also used Chamberland porcelain filters to demonstrate the
filterability of the agent of tobacco mosaic disease
○ Discovered that the disease could
not be due to a toxin
■ Filtered sap from infected
plants could be used for serial
transmission of the disease
without loss of potency
● Loeffler and Frosch → identified the first
filterable agent from animals
(foot-and-mouth disease)
● Walter Reed → described the yellow fever
virus (filterable agent)
● Bacteriophages: Filterable agents
○ Useful in studies on viral replication and bacterial genetics
● Method of classification of viruses → based on these criteria
○ The type of nucleic acid
○ The symmetry of the virus
○ The presence or absence of an envelope
○ The diameter of the nucleocapsid (helical viruses) or the number of
capsomeres (icosahedral viruses)
1
,Chapter 2 - Subdivisions, Classification and
Morphological Characterization of Infectious
Agents
● Living cells → divided into 2 groups
○ Eukaryotes
○ Prokaryotes
● Organisms in the domains Archaea and Bacteria → prokaryotes
Microscopical Techniques
● Common techniques employed for the examination of microorganisms + the
particular types of microorganisms for which the techniques are appropriate
2
,Pathogenic Microorganisms
● Pathogenic microorganisms: microorganisms that can cause disease in
animals/humans
Bacteria
● Unicellular + small + less complex than eukaryotic cells
● Rigid cell walls containing a peptidoglycan layer, multiply by
binary fission and exhibit considerable morphological
diversity
○ Rods, cocci, helical forms, and branching filaments
● Length: 0.5-5 µm
● Motile bacteria → possess flagella to move around through
liquid
Fungi
● Large group of non-photosynthetic eukaryotes
● Unicellular or multicellular
○ Multicellular fungi → produce moulds (filamentous
microscopic structures)
■ In moulds → cells are cylindrical + attached
end to end forming branched hyphae
○ Unicellular fungi → have a spherical or ovoid shape
+ multiply by budding
● Can secrete potent enzymes that can digest organic matter
● Moisture in environment → favourable
○ Can degrade a wide variety of organic substances
● Small number of fungi → pathogenic
Algae
● Considered plantlike → contain chlorophyll
● Many are free-living in water
● Some grow on surfaces of rocks/other structures in the environment
● Produce pigments which impart distinct coloration to water surfaces
● High water temperatures → growth → production of toxins
Viruses
● Acellular
● Virus particle/virion
○ Nucleic acid → DNA or RNA
○ Enclosed in a protein coat → capsid
○ Some viruses → surrounded by envelopes
● Size: 20-300 nm
● Occur in many shapes
3
, ○ Spherical, brick-shaped, bullet-shaped, elongated, etc.
● Lack the structures + enzymes necessary for metabolism and independent
reproduction → can only multiply withing living cells
● Bacteriophages: viruses that invade bacterial cells
Prions
● Prions: infectious particles that are smaller than viruses and have been implicated in
the neurological diseases of animals
● Distinct from viruses + appear to be devoid of nucleic acid
● Composed of abnormally-folded protein capable of inducing conformational changes
in homologous normal host cell protein
○ Structurally-altered abnormal protein accumulates in + damages long-lived
cells (e.g. neurons)
● Exhibit remarkable resistance to physical and chemical inactivation procedures
Biological Classification and Nomenclature
● Taxonomy: the practice and science of orderly classification of organisms into taxa
○ 3 interrelated parts
■ Identification
■ Nomenclature
■ Classification
○ Important in microbiology because
■ It permits accurate identification of organisms
■ It provides precise names that permit efficiënt communication
■ It groups similar organisms in a way that allows predictions to be
made and hypotheses to be framed with reasonable confidence
regarding members of the same group
○ Phenotypic characteristics used in taxonomy
■ Morphology
■ Metabolism
■ Physiology
■ Cell chemistry
■ Motility
○ Genetic methods used in taxonomy
■ DNA profiling
■ DNA-DNA hybridization
■ Multilocus sequence typing (MLST)
■ Percentage of guanine + cytosine in an organism’s DNA (GC ratio)
● Microorganisms → named according to the binomial system → in italics
○ 2 parts → capitalized generic name + specific epithet
○ e.g. Bacillus anthracis
■ Bacillus → generic name
■ anthracis → specific name
● Taxonomy of viruses
○ It is considered unlikely that viruses evolved from a single original protovirus
→ the highest level recognized is ‘order’
4
Chapter 1 - Microbiology, Microbial Pathogens and
Infectious Disease
● Founders of modern microbiology: Louis Pasteur and Robert
Koch
● Pasteur’s germ theory of disease → “germs” lead to disease
● Koch’s postulates → principles for proving that a specific
microorganism caused a particular disease
○ The pathogenic microorganism must be present in
every case of the disease but absent from healthy
animals
○ The suspected microorganism must be isolated and
grown in pure culture
○ The same disease must occur when the isolated
microorganism is injected into healthy susceptible
animals
○ The same microorganisms must be isolated again
from the injected animals which developed disease
● Dmitri Ivanovski → used Chamberland porcelain filters designed to remove bacteria
from drinking water
○ Transmitter tobacco mosaic disease from diseased to healthy plants
● Martinus Beijerinck → Also used Chamberland porcelain filters to demonstrate the
filterability of the agent of tobacco mosaic disease
○ Discovered that the disease could
not be due to a toxin
■ Filtered sap from infected
plants could be used for serial
transmission of the disease
without loss of potency
● Loeffler and Frosch → identified the first
filterable agent from animals
(foot-and-mouth disease)
● Walter Reed → described the yellow fever
virus (filterable agent)
● Bacteriophages: Filterable agents
○ Useful in studies on viral replication and bacterial genetics
● Method of classification of viruses → based on these criteria
○ The type of nucleic acid
○ The symmetry of the virus
○ The presence or absence of an envelope
○ The diameter of the nucleocapsid (helical viruses) or the number of
capsomeres (icosahedral viruses)
1
,Chapter 2 - Subdivisions, Classification and
Morphological Characterization of Infectious
Agents
● Living cells → divided into 2 groups
○ Eukaryotes
○ Prokaryotes
● Organisms in the domains Archaea and Bacteria → prokaryotes
Microscopical Techniques
● Common techniques employed for the examination of microorganisms + the
particular types of microorganisms for which the techniques are appropriate
2
,Pathogenic Microorganisms
● Pathogenic microorganisms: microorganisms that can cause disease in
animals/humans
Bacteria
● Unicellular + small + less complex than eukaryotic cells
● Rigid cell walls containing a peptidoglycan layer, multiply by
binary fission and exhibit considerable morphological
diversity
○ Rods, cocci, helical forms, and branching filaments
● Length: 0.5-5 µm
● Motile bacteria → possess flagella to move around through
liquid
Fungi
● Large group of non-photosynthetic eukaryotes
● Unicellular or multicellular
○ Multicellular fungi → produce moulds (filamentous
microscopic structures)
■ In moulds → cells are cylindrical + attached
end to end forming branched hyphae
○ Unicellular fungi → have a spherical or ovoid shape
+ multiply by budding
● Can secrete potent enzymes that can digest organic matter
● Moisture in environment → favourable
○ Can degrade a wide variety of organic substances
● Small number of fungi → pathogenic
Algae
● Considered plantlike → contain chlorophyll
● Many are free-living in water
● Some grow on surfaces of rocks/other structures in the environment
● Produce pigments which impart distinct coloration to water surfaces
● High water temperatures → growth → production of toxins
Viruses
● Acellular
● Virus particle/virion
○ Nucleic acid → DNA or RNA
○ Enclosed in a protein coat → capsid
○ Some viruses → surrounded by envelopes
● Size: 20-300 nm
● Occur in many shapes
3
, ○ Spherical, brick-shaped, bullet-shaped, elongated, etc.
● Lack the structures + enzymes necessary for metabolism and independent
reproduction → can only multiply withing living cells
● Bacteriophages: viruses that invade bacterial cells
Prions
● Prions: infectious particles that are smaller than viruses and have been implicated in
the neurological diseases of animals
● Distinct from viruses + appear to be devoid of nucleic acid
● Composed of abnormally-folded protein capable of inducing conformational changes
in homologous normal host cell protein
○ Structurally-altered abnormal protein accumulates in + damages long-lived
cells (e.g. neurons)
● Exhibit remarkable resistance to physical and chemical inactivation procedures
Biological Classification and Nomenclature
● Taxonomy: the practice and science of orderly classification of organisms into taxa
○ 3 interrelated parts
■ Identification
■ Nomenclature
■ Classification
○ Important in microbiology because
■ It permits accurate identification of organisms
■ It provides precise names that permit efficiënt communication
■ It groups similar organisms in a way that allows predictions to be
made and hypotheses to be framed with reasonable confidence
regarding members of the same group
○ Phenotypic characteristics used in taxonomy
■ Morphology
■ Metabolism
■ Physiology
■ Cell chemistry
■ Motility
○ Genetic methods used in taxonomy
■ DNA profiling
■ DNA-DNA hybridization
■ Multilocus sequence typing (MLST)
■ Percentage of guanine + cytosine in an organism’s DNA (GC ratio)
● Microorganisms → named according to the binomial system → in italics
○ 2 parts → capitalized generic name + specific epithet
○ e.g. Bacillus anthracis
■ Bacillus → generic name
■ anthracis → specific name
● Taxonomy of viruses
○ It is considered unlikely that viruses evolved from a single original protovirus
→ the highest level recognized is ‘order’
4
