Microbiology 2nd edition
Chapter 4
Most successful pathogens are not highly virulent, because when the host dies quickly, it
would prevent the spread of the pathogen to other hosts.
Organisms:
- prokaryotes = bacteria and archaea. They do not have a nucleus or any other
structures enclosed by a membrane.
- eukaryotes = have a nucleus, and organelles outside the nucleus and within the
membrane.
Bacteria
Streptococcus pneumoniae – diplococci
Streptococcus pygenes – streptococcus (chain)
Gram stain
1. first apply crystal violet -> all cells become purple
2. add Iodine -> all cells stay purple
, 3. decolorize with alcohol and wash with water -> gram+ stays purple, gram- cells
are uncolored.
4. Apply safranin -> gram+ are purple, gram- are pink.
Host-pathogen relationships
Pathogens = organisms that can infect humans and cause illness in them.
Mutualistic relationship = pathogen depends on the host for survival and the host
benefit from their presence.
Opportunistic pathogens = organisms that take advantage of a host increased
susceptibility to infection. Under normal conditions these organisms are not pathogenic.
Primary pathogens = can cause disease in healthy individuals.
Requirements infections:
1. be able to multiply in sufficient numbers to secure establishment in the host.
2. Be transmissible to new hosts.
Bacterial pathogenicity and virulence
Pathogen must adhere, penetrate and persist in the host cell. It must be able to avoid,
evade or compromise the host defense mechanisms. It must damage the host and permit
the spread of the infection. It also must be able to exit from one host and infect another
host.
Virulence= how harmful a pathogen is for the host.
Pathogens have clusters of genes whose activity results in the production of factors that
increase the virulence of the pathogen. These genes are carries on plasmids en they can
transfer to other bacteria. These virulence genes are called pathogenicity islands. Some
virulence genes are regulated by quorum sensing.
During quorum sensing, proteins relay information about the cell’s environment. It is
based on cell population densities (certain genes are expressed only when there is a
high population density). Bacteria delay the production of toxins to hide from the host
defenses, which has no trouble in dealing with a small amount of pathogens.
Auto-induction is communication between bacteria via sensing proteins. These other
bacteria then wait before starting the transcription of toxin genes until there are enough
pathogens.
Biofilm= adherence and growth of multiple bacteria.
Quorum sensing also regulates biofilm formation. Biofilm is very difficult to remove. It is
a challenge for health care, but it is also able to capture nutrients, and thereby allowing
the bacterial population to increase.
The body usually reacts by coating it with a protein film, which is composed fibronectin,
fibrinogen, albumin, immunoglobulins and other proteins that serve as bindingsites and
receptors of bacteria. Bacteria begin to accumulate on this protein film and form a
biofilm. Large pieces of biofilm can form clots and cause tromboembolisms.
, The host cell
Fungi and human cells – eukaryotic
Bacteria and archaea – prokaryotic
Prokaryotic cells Eukaryotic cells
Single chromosome Paired chromosome
Genetic material in nuclear region Genetic material in membrane closed
nucleus
Absence of histones Presence of histones
Extrachromosomal DNA in plasmids Extrachromosomal DNA in mitochondria
and plasmids
Absence of ER Presence ER
Absence of Golgi Presence of Golgi
Ribosomes 70S Ribosomes 80S in cytoplasm and ER, 70S
in mitochondria
Cell wall: peptidoglycan, LPS, teichoic acid No cell wall in animal cells, chitin in fungal
cells
Pili present Pili absent
Flagella present Flagella present in certain cell types
Asexual reproduction Sexual or asexual reproduction
Plasma membrane
= the outer layer of the eukaryotic cell. Contains cholesterol in human cells and in fungal
cells ergosterol.
The eukaryotic membrane is made up of a phospholipid bilayer. It has polar, hydrophilic
heads ands non polar, hydrophobic, fatty acid tails. A variety of proteins move freely
through the lipid bilayer.
Components of the eukaryotic plasma membrane:
- filaments of cytoskeleton
- glycoproteins
- carbohydrates
- glycolipid
- cholesterol
- integral protein
- peripheral protein
- extracellular matrix fibers
Influenza virus attaches to receptors on the plasma membrane.
Cytoplasm
It is made up of the cytosol, organelles and structures that are not enclosed by a
membrane.
Cytoskeleton
Chapter 4
Most successful pathogens are not highly virulent, because when the host dies quickly, it
would prevent the spread of the pathogen to other hosts.
Organisms:
- prokaryotes = bacteria and archaea. They do not have a nucleus or any other
structures enclosed by a membrane.
- eukaryotes = have a nucleus, and organelles outside the nucleus and within the
membrane.
Bacteria
Streptococcus pneumoniae – diplococci
Streptococcus pygenes – streptococcus (chain)
Gram stain
1. first apply crystal violet -> all cells become purple
2. add Iodine -> all cells stay purple
, 3. decolorize with alcohol and wash with water -> gram+ stays purple, gram- cells
are uncolored.
4. Apply safranin -> gram+ are purple, gram- are pink.
Host-pathogen relationships
Pathogens = organisms that can infect humans and cause illness in them.
Mutualistic relationship = pathogen depends on the host for survival and the host
benefit from their presence.
Opportunistic pathogens = organisms that take advantage of a host increased
susceptibility to infection. Under normal conditions these organisms are not pathogenic.
Primary pathogens = can cause disease in healthy individuals.
Requirements infections:
1. be able to multiply in sufficient numbers to secure establishment in the host.
2. Be transmissible to new hosts.
Bacterial pathogenicity and virulence
Pathogen must adhere, penetrate and persist in the host cell. It must be able to avoid,
evade or compromise the host defense mechanisms. It must damage the host and permit
the spread of the infection. It also must be able to exit from one host and infect another
host.
Virulence= how harmful a pathogen is for the host.
Pathogens have clusters of genes whose activity results in the production of factors that
increase the virulence of the pathogen. These genes are carries on plasmids en they can
transfer to other bacteria. These virulence genes are called pathogenicity islands. Some
virulence genes are regulated by quorum sensing.
During quorum sensing, proteins relay information about the cell’s environment. It is
based on cell population densities (certain genes are expressed only when there is a
high population density). Bacteria delay the production of toxins to hide from the host
defenses, which has no trouble in dealing with a small amount of pathogens.
Auto-induction is communication between bacteria via sensing proteins. These other
bacteria then wait before starting the transcription of toxin genes until there are enough
pathogens.
Biofilm= adherence and growth of multiple bacteria.
Quorum sensing also regulates biofilm formation. Biofilm is very difficult to remove. It is
a challenge for health care, but it is also able to capture nutrients, and thereby allowing
the bacterial population to increase.
The body usually reacts by coating it with a protein film, which is composed fibronectin,
fibrinogen, albumin, immunoglobulins and other proteins that serve as bindingsites and
receptors of bacteria. Bacteria begin to accumulate on this protein film and form a
biofilm. Large pieces of biofilm can form clots and cause tromboembolisms.
, The host cell
Fungi and human cells – eukaryotic
Bacteria and archaea – prokaryotic
Prokaryotic cells Eukaryotic cells
Single chromosome Paired chromosome
Genetic material in nuclear region Genetic material in membrane closed
nucleus
Absence of histones Presence of histones
Extrachromosomal DNA in plasmids Extrachromosomal DNA in mitochondria
and plasmids
Absence of ER Presence ER
Absence of Golgi Presence of Golgi
Ribosomes 70S Ribosomes 80S in cytoplasm and ER, 70S
in mitochondria
Cell wall: peptidoglycan, LPS, teichoic acid No cell wall in animal cells, chitin in fungal
cells
Pili present Pili absent
Flagella present Flagella present in certain cell types
Asexual reproduction Sexual or asexual reproduction
Plasma membrane
= the outer layer of the eukaryotic cell. Contains cholesterol in human cells and in fungal
cells ergosterol.
The eukaryotic membrane is made up of a phospholipid bilayer. It has polar, hydrophilic
heads ands non polar, hydrophobic, fatty acid tails. A variety of proteins move freely
through the lipid bilayer.
Components of the eukaryotic plasma membrane:
- filaments of cytoskeleton
- glycoproteins
- carbohydrates
- glycolipid
- cholesterol
- integral protein
- peripheral protein
- extracellular matrix fibers
Influenza virus attaches to receptors on the plasma membrane.
Cytoplasm
It is made up of the cytosol, organelles and structures that are not enclosed by a
membrane.
Cytoskeleton
