lectures 1-6 Flashcards
bacteria world
what is the importance of studying bacteria?
antimicrobial resistance 10 m deaths by 2050
where are bacteria found?
Plants
Animals
Soil
Water
Air
Arctic Ice
Volcanic vents-
huge diversity
what is the capsule for?
protection
what is the cell wall for?
structure
pilus
attachment
flagella
movement
features of bacteria
No mitochondria – functions performed by cytoplasmic
membrane
* Ribosomes (70S - 30S and 50S subunits) free in the
cytoplasm or bound to inner face of cytoplasmic membrane
– no ER
* Single chromosome (nucleoid) – no nuclear membrane
where does transcription and translation occur?
cytosol
gram positive have
thick wall of peptidoglycan
what is peptidoglycan for?
binary fission, die slowly without.
what are l form bacteria?
L-forms are bacterial variants that lack a cell wall and divide by a variety of processes involving membrane blebbing, tubulation, budding resistance to antibiotics
why is cell wall important?
- It is essential for viability
- It is one of the most important sites for attack by antibiotics
- It provides ligands for adherence and receptor sites for drugs
or viruses - It is a ”microbial associated molecular pattern” that is recognised by
host recognition proteins – activates host signalling cascades
peptidoglycan made of what?
Glycan chains connected by peptide crosslinks,B-1,4 glycosidic linkages
what are the residues?
N-acetyl muramic acid N-acetyl glucosamine
d- alanine dimers do what
direct cross link to L-diaminopimelic acid (free amino group)
what is lost during cross linking
5th amino acid lost during
cross-linking!
diversity of bacteria
in population of bacteria each cell is unique mutant variety’s
cell envelope
Elements of the cell envelope that help bacteria
adhere to surfaces, escape the immune system
& cause disease
Gram-negative cell envelope
Inner membrane:
Phospholipid on
inner and outer face
Outer membrane:
* Phospholipid inner face
* LPS outer face
what is lps
Lipopolysaccharides (LPS)
what does lps do ?
1.LPS is a barrier against hydrophobic agents, detergents, bile,
antibiotics
2. Forms a very tightly packed layer – strong lateral interactions
between LPS molecules
3. Proinflammatory – Interacts with receptors on macrophages and Bcells leading to cytokine release – can cause endotoxic shock.
TLR4 ligand
Binds to TLR4 and triggers
upregulation of pro-inflammatory cytokines.
This can cause entotoxic shock.
how many forms of lps
3 forms of lps
what are the 3 forms of lps
rough smooth and lipid a
rough lps has
poor adherence to host cells
Because rough lps has shit adherence why would they lose the o- antigen that makes it smooth?
O-antigen targeted by antibiotics,
host immune cells, antimicrobial
peptides and bacteriophages
Loss of O-antigen allows bacteria to
“hide” from host
Modification of LPS also possible
Vibrio cholerae what happens when its modified o antigen?
lipid a is modified Host antimicrobial peptides (CAMP’S) recognise lipid A
Amino-acid (glycine) modification of lipid A
gram positive cell envelope
- Teichoic acids
- Cell wall anchored
proteins (covalently
bound)
what are tectonic acids?
Teichoic acids are
negatively charged polymers
Role of Teichoic Acids
Binding to receptors
and surfaces
Negative surface
charge
Protection from
harmful molecules
antibiotics
Cation homeostasis
Growth and
division
Modifications of Teichoic acids
d-Alanine – increased
resistance to host defenses,
antimicrobial peptides,
glycopeptide antibiotics
Glycosylation – increased
protection from immune
system
Modifications are not always beneficial
Glycosylation may increase susceptibility
to bacteriophages
D-alanine modifications can reduce ability
to adhere to host cells and establish an
infection
what is for attachment of bacteria gram positive?
Cell wall anchored proteins are
synthesised in the cytoplasm
* They are translocated across
the cytoplasmic membrane
(secretion)
* They become covalently
anchored to peptidoglycan and
displayed on the bacterial surface
* Key role in attachment /
adhesion
sortase enzymes do what?
In Gram-positive bacteria proteins are displayed on the cell surface using sortase enzymes.
Capsules, EPS and biofilms – what do
they have in common?
Outermost layer of protection
* Common structure, biogenesis and export pathways
* Assist in adhesion to solid surfaces
* Protect against antibiotics, antimicrobial peptides and host
immune responses
* Make infections hard to treat
what are capsules?
a biofilm for one.
Capsule is a type of
glycocalyx (sticky sugar
coat)
Distinct, gelatinous = Capsule
* High water content
* Important for virulence –
resists phagocytosis
opsonins
Opsonins directed to cell envelope components are
deposited beneath the capsular layer.
opsin reseptors triger phagocytosis.Capsule inhibits access to opsonins
Serotype =
grouping bacteria based
on cell envelope surface structures
Extracellular polysaccharides (EPS) what are they
EPS form the biofilm matrix. for eample the three types 1.Soft, loose polymer 2.Fabric-like matrix3. Tight scaffold
biofilms are
- Impervious to phagocytosis by
neutrophils and macrophages - Resistant to antimicrobial peptides and
complement - Semi-dormant - difficult to inhibit with
antibiotics
the s layers are what
chainmail- Extracellular layer coating the entire bacterial cell
surface
s layer
Composed of protein or glycoprotein
Functions of S-layer
Molecular sieve
Cut-off determined by size and
morphology of pores
* Protection
Resistance to bacteriophage,
complement, phagocytosis, extreme
environments
* Adhesion to host cells
Scaffold for adhesion proteins
Fimbriae
Help attach cells to a solid
surface or tissues
* Help bacteria cling together
pili
Longer, fewer and thicker tubes (1-2 per cell)
* Made of Pilin protein
* Sex pili (conjugation) and ordinary pili
* Attach to other bacteria
* Motility (crawling/twitching)
* Mostly Gram negative
