Lecture 11 Flashcards
What are capsules, slime layers, and S-layers together knonw as
the extra polymeric substance: layer of material outside the cell wall usually composed of polyscaccarhide, can contain poly D-glutamic acid
How is the prescence of the extra polymeric substance determined
geneticially, but physicoloigcal, nutritional conditions can alter it spresence
Whats a apsule
when the EPS is well organized, not easily removed (clear halo)
Whats a slime layer
when the EPS is diffuse, unorganized and easliy removed
Whats a glucocaluz
a network of polysaccharides extending from the
bacterial surface (can include both a capsule and a slime layer) and
aids in bacterial attachment to surfaces (fibrillar in nature)
Whats a biofilm
polymeric matrix of microbial origin in which microbes of the
same or different species are embedde
Whats a S-layer
made up of a single protein or glycoprotein
Facts of capsules
– not required for bacterial growth or reproduction in the laboratory
– provide advantages in the normal habitats
– help to resist phagocytosis
Advantages of capsules
- prevent drying
- protection against toxins; decreased sensivity to antibiotics
- increased adherence
- decreased phagocytosis
- increased killing of WBCs
Why is there decreased phagocytosis by neutrophils and macrophages (WBCs).
since phagocytes can’t adhere to most of the capsule types on S.
pneumoniae
How does it increase killing of WBC in streptococcus pyogenes
releasing a protease that cleaves a complement factor inhibiting ability to attract phagocytes -> avoids the alternative compleemtn pathway
How does it increase killing of WBC in Staphylococcus aureus
leukocidins
How are non-encapsulated bacteira
decreased adherence to mammalian tissue
– increased phagocytosis
– little of no killing of WBCs
– more sensitive to certain antibiotics
Are capsules considered a virulence factor
Yes
other advantages
- virulence factor
- protects against desiccation, exclude hydrophobic toxic substances like detergents and bacterial viruses
- directly contribute to pathogenitiy
How does purtussis cause whooping cough
produces a thick gummy capsule that paralyzes the cilia on the respiratory epithelium and mechaniclaly blocks the availability of air -> lung tisuse
Role of capsules in specific adherance?
attachment of Rhizobium to legume root tips using the capsule:
different species attach to very specific legumes: R. japonicum attaches
specifically to soy beans
Role in non-specific adherance?
attachment of Streptococcus mutans to teeth in the presence of
sucrose due to capsule production versus no attachment in the presence
of glucose : since no capsule is present (basis of sucrose-less gums and
candies)
Is dental plaque
biofilm
Summary of EPS advantages
- prootection from host defenses
- a role in specific adherence
- a role in non-specific adherence
protection from harsh environmental conditions (e.g., desiccation) - protection from viral infection or predation by bacteria
- protection from chemicals in environment (e.g., detergents)
- protection from antibiotics by reducing permeability
- motility of gliding bacteria
- protection against osmotic stress
What are biofilms
organized communities of microorganisms, usually found in defined
layers strongly associated with a surface and enclosed in a matrix of
polysaccharid
Can biofilms consist of 1 more type of organism?
Can consist of more than one type of organism, can even include both
prokaryotes and eukaryotes, starts with the attachment of one type of
bacteria
Biofilms requier
requires cell-cell communication molecules
- adhesiveness, capsule pili
Biofilms are sosciared with
ssociated with many surfaces such as teeth, prosthetic devices,
catheters, storage containers, contact lenses, water pipes, leaves of certain
plants
* can be an important medical problem if growth on various medical devices
can’t be controlled
Whats planktonic
bacteria can either exist in a mobile, ‘planktonic’ state where they freely disperse and explore their environment for nutrients, or stay statically as ‘biofilms
organisms embedded in a biofilm do not have the same growth
characteristics as they have in suspension culture. why?
biofilms often resistant to antibiotics can give 1000 fold
increased resistance)
biofilm cells do not express their
flagella
Funciton of biofilm
Biofilm formation: fortress matrix enable cells to survive
desiccation: requires a surface and results in sequestering fr
the environment:
- result improved nutrient acquisition
- protection agaist antibiotics
What are the steps to bacterial biofilm formation
(A) Reversible attachment.
(B) Irreversible attachment.
(C) Bacterial cells synthesize and
secrete EPS.
(D) Maturation.
(E) Dispersal
What happens when bacteria slough off the biofilm
when bacteria slough off the
biofilm can provide source of
infection for other parts of the
body
A mature biofim has
cell aggregates with pores
to allow nutrients to reach cells (channels are shaped
by protozoa that feed on the bacteria)
Whats the cell to cell communication signalling moelcule
N-acylhomoserine lactone (AHL)
Quorum sensing in biofilm
use autoinducers that
coordinate behaviours based on cell
density: both within species and
between
How does quorum sensing work
indivudally -> quorum sensing off
group -> quorum sensing off
positive feedback loop -> creases for AI -> increases cell desnity
negative feedback loop -> less AI -> decrease poplaton
How does AI induce the bacteria
Bacteria produce sginalling moelcules called autoinducers.
bacteria have a receptor that can detect the inducer
indcer binds. -> activates transdiction for certain genes as well as those for inducer syntheiss -> more AI
The autoinducer N-acyl homoserine lactones (HSL) is also known as
pheromones
Quorum-sensing circuits and biofilm formation differences in gram - and gram +
gram -: sty secreted in the intermembrane and becomes autoinducer -> doesnt get out, acts on itself
gram (+) autoinducers are in the cell membrnae, can diffuse outcan can be released by 1 bacterial cell and captured by another, or it can capture itslef
What are pili/firimiae
short, thin, hairlike, proteinaceous appendages, thinner than flagella
more common in gram negative than gram positive
How are pili distinguished
types of pili are distinguished primarily by serology (immunological
relatedness) rather than by morphology
Types of pili
many different types of pili can be found among different bacterial
species and within a single bacterial species
not all pili are present at one time (E.coli usually expresses 2-4 types
of pili at any given time)
Function of pili
mediate attachment to surfaces
often contain specific and non specific adhesions that bind to different
host receptors
Genes that encode pili
genes that encode proteins involved in pilus synthesis and assembly can
be located on both plasmid and bacterial chromosomes
What are sex pili
similar to fimbriae except longer, thicker, and less numerous (1-10/cell)
– required for mating, indirectly involved in antibiotic resistance (i.e. F
plasmids can spread these genes)
Do Streptococcus pneumoniae have capsules
when it lacks a capsule is easily destroyed by the host cell (no disease),
with a capsule cause pneumonia
theres multiple different types of capsules
How are adhesive pili virulent
often the primary factor associated with colonization and disease e.g. in
pathogenic strains of E. coli, Salmonella, Neisseria
antiphagocytic properties and the increased ability to adhere and colonize -> enhanced pathogenicity
What are p-pili
(anchored in outer membrane)
intestinal E.coli
(10% of the pili on the cell) and uropathogenic E.coli cause urinary tract infections and infections of the kidneys and bladder (cysititis)
binding of glycolipids in the urinary tract mucosa
What are type IV pili (anchored in inner membrane)
ound on other pathogens such as N.
gonorrhea and V. cholerae
some type IV fimbriae (pili) are required for twitching motility or gliding
motility that occurs in some bacteria and are found on the ends of the cell
twitching motility has a role in
biofilm formation
K88 pili
Enterotoxigenic
encoded by plasmid associarted with diarrhea
bind to mannose on glycoproteins of ileum mucosa (upper GI)
difference in pili structure for gram neg and gram pos
gram neg: embeeded in the outer membrane, can be embedded in the inner
gram pos: covaletnely attached to peptidoglycan
do pilis bind to receptors
often contain specific and non specific adhesions that bind to different
host receptors
Whats flagella also known as
H - antigen
Does the strcucutre of bacterial flagellum differs completely from that of the
eukaryotic flagellum
yes
system and function of flagella
elaborate sensory and response system that enables bacterial cells
to obtain nutrients and to avoid toxic conditions using a reversible motor
can in some cases be used to identify specific bacterial cell types
How are flagella immungogen
- one of the components of bacterial
cells to which the host make antibodies
How is flagella a virulence facot
- appear to exhibit antigenic variation
- some flagellae have adhesions
flagellae are exposed on the surface of the cells, antibodies to
flagellae are usually protective against subsequent infections by
organisms having the same immunogens in their flagella
monotrichous
one flagellum
polar flagellum
flagellum at end of cell
amphitrichous
one flagellum at each end of cell
lophotrichous
cluster of flagella at one or both ends
peritrichous
spread over entire surface of cell
bacterial flagella in gram negative structue
four rings connect ultrastructure of bacterial flagella
to a central rod:
L and P ring associate
with LPs and peptidoglycan,
M ring the P.M
bacterial flagella in gram positive structue
two rings:
one ring to P.M.
and the other
to peptidoglycan
there is an additonal ring on the cytoplasmic face
acts as signal receiving device for chemotaxis,
energy generator (proton [H+] flux that drives rotation),
rotation generator i.e. the motor Brunt 2025
What is the filament
- hollow, rigid cylinder that can be up to 10 times the length of the cell
- tructure is wave-like
- omposed of a single protein flagellin
- there are many different variations of flagellin, the exact type of flagellin present
depends on the species and strain - unsual amino acid compositio
- it is the filament that freely rotates (clockwise or counter clockwise
What allows the host to recognize flagella as forein
unusual amino acid ε-methyl-lysine (flagella antigens)
How are gram negatives serologically identified
based on O-antigens (LPs) and H antigens
(flagellar) and K antigens (capsule): e.g.
highly pathogenic strain E. coli is referred
to as E.coli O157: H7
Whats the Mechanism of Flagellar
Movement
- counterclockwise rotation causes
forward motion - clockwise rotation disrupts run causing a
tumble
flagellar rotation counterclockwise
organism swims towards the
effector
flagellar rotation clockwise
the organism tumbles and movement
is away from the effector
What is Chemotaxis?
movement towards a chemical attractant or away from a chemical repellant
concentrations of chemoattractants and chemorepellants detected by chemoreceptors on surfaces of bacterial cells which transduce the signal to the flagellae
Flagellar motility: direction is determined by
- the conformation of the
gear shift complex associated with the C-ring of the basal body - Effectors indirectly determine the gear shift conformation via a signal
transduction pathway
directed movement is caused byb
lowering the
frequency of
tumbles as
bacteria move up
gradient
Mechanism of chemotaxis: signal
transduction
- complex but rapid
- involves conformational changes in proteins
involves methylation or phosphorylation of
proteins in a relay system
How does the flagella sense
chemical -> chemoreceptors -> induce flagella
the rotational direction of the flagella requires
modulation of the activity of the
phosphorelay system
Phosphorylation of proteins leads to
clockwise direction
dePhosphorylation of proteins leads to
anticlockwise directo
What are the events in spore formation
Starts with a vegetative cell. On starvation, spores are produced
-> sporulation.
on unfavorable conditions, spores are released out of vegatative cells and remain dormant
When conditons are favoruable again -> germinatin
Which bacteria forms the bacterial endospore
Gram positive rods, Bacillus and Clostridium
dormant stage is not a..
reproductive stage
What makes endospores so resistant
calcium (complexed with dipicolinic
acid) in the thick spore coat
acid-soluble, DNA-binding proteins
dehydrated core
contains DNA repair enzymes/ nuclear
material for formation of vegetative cells
What is involved in sporulation
phosphor-relay, posttranslational
modification of proteins, transcription initiation
regulatory proteins, and alternative sigma
factors play a role
- invoves many gens
The process of sporulation ends with
death by lysis of the
‘‘mother cell’’ and the formation of a dormant
daughter cell(the spore Brunt 2025 )
ratio of cell: spore
1 cell/spore
How does the prorogensis happen
normally commences when growth ceases
because of lack of nutrients, waste build up
complex multistage process to form spore
involving significant change in gene
expression:
endospores will germinate (multistage
process) when returned to a positive nutrient
environment -> vegetaitiv cell
What is the master key that determines the switch between vegetative division and sproulaiton
protein Spo0A . controlled by reversible phosphorylationdephosphorylation mechanism
unphosphorylated form -> Spo0A is inactive
phosphorylated form, it is both an
activator of the transcription of sporulation genes and a negative regulator of genes that prevent sporulation.
in its unphosphorylated form,
Spo0A is
in active
in its phosphorylated form Spo0A is
both an
activator of the transcription of sporulation genes and anegative regulator of genes that prevent sporulation.
