Flashcards
Bacterial form and function
Flashcards do conjunto (53)
- 1Bacterial functionsInvasion
Motility
Attachment/adhesion - 2Importance of bacterial surface moleculesContribute to motility, adhesion, invasion and resistance
Harbour molecular patterns that trigger immune responses
Targets for components of the complement/immune system - 3GP cell envelopeCytoplasmic membrane
Thick peptidoglycan - reaches 160nm thickness in streptococcus pneumoniae
Teichoic acid - 4GN cell envelopeCytoplasmic membrane
Thin peptidoglycan (3nm)
Outer membrane
Lipopolysaccharide - 5PeptidoglycanComplex molecule found only in bacterial cell walls.
Provides rigid support and helps maintain shape.
Polymer of (1-4)-linked N-acetyl glucosamine and N-acetyl muramic acid
MurNac is substituted with peptides, typically 3-5 alternating L- and D- amino acids
Peptides from adjacent strands are often cross-linked directly or through short peptides - 6Different forms of peptidoglycanThe differences are due to a difference in composition of the peptide chains
mDAP peptidoglycan is largely found in Gram negative bacteria and has a mDAP (derivative of lysine) at the third position on the chain. Cross linking of parallel glycan chains is usually by direct peptide bond formation between the peptide bridges
L-lys peptidoglycan is found mostly in Gram positive bacteria and cross links via glycine bridges - 7Exception to the peptidoglycan ruleBacillus sp and Listeria sp have mDAP in their peptidoglycan
- 8mDAPDiaminopimelic acid
- 9Peptidoglycan detectionDuring bacterial growth there is turnover and synthesis of new peptidoglycan to accommodate changes in cell shape and size. This occurs through the balance between degradation of existing peptidoglycan and synthesis of new chains. During this process, small peptidoglycan fragments are either recycled or shed from bacteria and the shed products are detected by intracellular NOD proteins
- 10NOD proteinsHumans have 2 NODs that can detect peptidoglycan
NOD1: detects mDAP PGN
NOD2: detects PGN from both GP & GN
Activation of NOD1 & 2 activates the transcription factor NFkB resulting in the up-regulation of proinflammatory cytokines - 11Teichoic acidsPresent in Gram positive bacteria
Highly variable an ionic polymers
Proposed functions:
Cell shape, growth and division
Resistance to antimicrobial peptides
Possibly recognised by TLR2 - 12The outer membraneLipid bilateral with asymmetric lipid distribution
Inner leaflet: phospholipid
Outer leaflet: mostly LPS
Present in Gram negatives
Forms permeability barrier against agents such as bile and antimicrobials
Allows production of outer membrane vesicles which can have immunomodulatory effects
Target for insertion of MAC and bacterial lysis by complement
Antibiotics have to be modified to increase their permeability through the OM - 13Why the outer membrane is bad for the bacteriaCould be disadvantageous to the bacteria as it renders the bacteria more susceptible to lysis by the MAC of the complement system. GPs don’t have the OM so although MAC components get deposited, they don’t seem to have any lysis effect. A C5b-9 MAC forms normally on the GP surface and inserts normally into the cell wall, the PGN layer is too thick for the C5b-9 to reach the plasma membrane of GP organisms
- 14LipopolysaccharideKey MAMP of Gram negative bacteria
Important inducer of inflammatory response
Composed of:
Lipid A (endotoxin)
Core polysaccharides
O antigen - 15O antigen and core sugarsPolysaccharide chain
Highly variable except conserved core sugars (>160 different O antigens in E. coli strains)
Involved in virulence and pathogenesis
Length of O antigen affects invasion in Shigella
Molecular mimicry (copy host molecules and put them on their surface to avoid immune detection) - 16Rough and smooth LPSNot all bacteria have LPS with an O antigen - this determines whether the LPS is rough or smooth
Aside from the KDO, the O antigen and core can be highly variable
In E. coli there are more than 160 O antigens and these form the basis of serological typing of bacteria so when you hear about an outbreak by E. coli 0104 in 2011, it refers to the LPS type
There are more than 1500 LPS antigens in Salmonellaz - 17O-antigen lengthWork in shigella showed that the length of the O antigen can affect how well the bacteria can invade epithelial cells
- 18Molecular mimicrySome bacteria express polysaccharide which mimic host molecules. This molecular mimicry can have different effects, for example it can induce local immunity which can then damage cell barriers through antibody-mediated mechanisms, and increase invasion. Alternatively it can prevent Ab production and therefore act as a camouflage and escape the immune system. It can also allow binding to host lectins, or in some cases has been linked with autoimmune diseases such as guillan barre which can follow infection with campylobacter jejuni that expressed LPS which is a mimic of GM1 ganglioside
- 19O antigen in ShigellaShigella can display enhanced virulence as a consequence of altering the O antigen. West et al. (2005) used signature-tagged mutagenesis along with 3-D molecular modelling to predict that the bacteriophage encoded glycosylation of shigella O antigen 5a induced its transformation from a linear to helical confirmation. Consequently the LPS formed is more compact almost halving the distance it extends beyond the outer membrane. West et al. (2005) used Electron microscopy to confirm these predictions and demonstrate enhanced T3SS on the surface, which shigella uses to inject proteins into human cells leading to bacterial invasion and a vigorous inflammatory response. Thus LPS glycosylation promotes bacterial invasion as well as the invasion of innate immunity which may have contributed to the emergence of serotype diversity in shigella
- 20Lipid AEndotoxic portion of LPS.
Systemic inflammatory response syndrome: Fever, hypertension, DIC, activation of complement and macrophages.
Ligand of surface TLR4 leading to inflammatory cytokine production
inside cells binds caspase-4 leading to cell death.
Targeted by antimicrobial peptides - 21Hoffman (1996)Investigated have fruit flies combat infection using flies with mutations in several different genes including Toll. When Hoffman infected his flies with bacteria or fungi, he discovered that Toll mutants die because they could not mount an effective immune response. He was also able to conclude that the product of the Toll gene was involved in sensing pathogenic microorganisms and Toll activation was needed for successful defence against them
- 22Beutler (1998)Discovered that mice resistant to LPS had mutations in a gene that was quite similar to the Toll gene of the fruitfly. This Toll-like receptor turned out to be the elusive LPS receptor. When it binds LPS, signals are activated that cause inflammation, and when LPS doses are excessive, septic shock
- 23Why is it important to know if a bacterium is GP or GN?Helps with bacterial identification.
Susceptibility to complement, drugs and antibiotics.
Impact on immune activation and evasion - 24Important bacterial structuresCapsule
Flagella
Pili
Secretion systems
Toxins - 25Bacterial capsulesHigh molecular weight polymers on the surface of bacteria
Structurally diverse:
- over 90 capsule types in Streptococcus pneumoniae (serotypes)
- 13 capsules in Neisseria meningitidis
- 1 capsule type in Streptococcus pyogenes
Can be structural mimetic of host molecules:
- N. meningitidis serotype B capsule
Used in conjugate vaccines (Hib, Men, A, C, Y, W and X, Pneumococcal)
Important for resistance to immune defences - 26Hyams et al. (2009)Used established flow cytometry assays to show that unencapsulated streptococcus pneumoniae strains had a marked increase in the deposition of C3b/iC3bmin comparison to encapsulated strains and the capsules prevent complement deposition mediated by both the classical and alternative complement pathways. They also showed that an increase in C3b/iC3b deposition caused a markedly higher level of association of the bacteria with human neutrophils, suggesting a role of the capsule in the prevention of bacterial phagocytosis by neutrophils
- 27Geoffroy et al., 2003Used a high density signature-tagged transposon mutagenesis, followed by a large scale sequencing of the transposon insertion sites to construct a genome-wide collection, and found capsule negative mutants of Neiserria meningitidis were highly sensitive to killing in human serum, suggesting a role of the capsule in bacterial protection
- 28FlagellaLong, thin filaments involved in bacterial motility
Enable bacterial movement through rotation of the filament
Complex molecular nano-machines composed of approx. 25 different proteins
Three major components: basal body, hook and filament
Bacteria can express more than one flagellum, and they can be located at one end, both ends, or all over the cell
Present in both GP and GN bacteria but will have slightly different structures due to the different structures of the cell envelope - 29FilamentFormed of 20,000-30,000 flagellum subunits arranged into protofilaments which twist around one another to form the filament
Diameter of 23nm, central channel of approx. 2nm
Subunits assemble at distal end
Can adopt a variety of helical morphologies - 30HookComposed of FIgE (approx. 120 subunits)
Tightly controlled length (55+-6nm)
Bent region just outside the bacterial cell and it positions the flagellum at the correct angle so that when it rotates it works as a propellor to move the bacterium - 31Basal body (motor)MotA/MotB form stator complex
FliG/M/N form rotor/switch complex
Energised by proton motive force and comprised of a series of ring structures
Embedded in the inner and outer membrane - 32Flagella influence bacterial behaviourBy allowing the bacteria to swim, it can allow them to move. E.g. through chemotaxis, bacteria can sense the presence of food and swim towards it, or can swim away from toxic molecules
Flagella also contribute to movement for example in ascending infections in the urinary tract where bacteria can use flagella-based motility to go against the flow of urine
Through changing the speed and direction of rotation, they can use flagellum to enable attachment, while stopping movement entirely allows them to form biofilms, important for colonisation and persistent infections - 33Which PRR detects flagellin?TLR5
Flagellin has two domains, a variable region and a conserved region. This region is conserved because it is important for interactions of subunits in the protofilaments, and it is this conserved region that is engaged by the TLR and leads to activation of the immune response - 34PiliFilamentous surface structures
Variable length (up to several microns) and diameter, although they are shorter and thinner than flagella
Formed by polymerisation of pilin subunits
Many different types of pili - different length arrangements and sizes including bundle-forming pili which wrap together to form larger filaments
Important roles in pathogenesis (adhesion)
E.g. type I pili of Uropathogenic E. coli - 35Pili in pathogenesisCan be Important for DNA uptake and therefore contribute to genetic exchange
Confer a type of movement, known as twitching motility
Allow bacteria to form aggregates by pili from different bacteria binding to one another
Most famous for their roles in bacterial adhesion e.g. type 1 pili of UPEC - 36UPEC UTIMicrobial infiltration of the urinary tract
Lower: cystitis, prostatitis, urethritis
Upper: pyelonephritis - 37Acute cystitisUrinary urgency and frequency
Pain when voiding (dysuria)
Lower abdominal discomfort
Cloudy or dark urine - 38Acute pyelonephritisSudden onset
Chills, fever, malaise - 39UTI diagnosisPresence of RBCs, high nitrite levels and leukocyte esterase in urine
- 40UTI treatmentAntibiotics, 1% require hospitalisation
- 41Roles of type 1 and P-pili in pathogenesis of UPEC UTIsContamination of periurethral area with UPEC that has colonised the bowel
Adherence to uroepithelial cells by type 1 and P fimbriae
Invasion: intracellular multiplication observed for selected strains
Apoptosis and exfoliation of bladder epithelial cells
Influx of PMNs
Type 1 fimbriated E. coli selected at high colony forming units and low oxygen
E. coli ascends to kidney
P. fimbriae bind to renal tubular epithelial cells
Cytokines induced
Haemolysin damages epithelium
Sat vacuolates epithelial cell Andy damages glomeruli
E. coli crosses tubular epithelial cell barrier to initiate bacteraemia - 42Luminal surface of the bladder is lined byLayer of superficial facet/umbrella cells
Umbrella cells elaborate an asymmetric unit membrane (AUM)
AUM forms plaques covering the apical surface of the urothelium - 43AUM plaques containUroplakins
Four main components: uroplakins la, lb, ll, lll
Integral membrane proteins
Form particles arranged in a hexagonal lattice
Acquire mannose glycans in the ER during trafficking - 44FimH tip adhesion of UPEC type l pills bindsMannosylated uroplakins
- 45Why is it important to understand the molecular basis of UPEC adhesionInforms the design of anti-infectives
Structure-based discovery of glycomimetic FmlH ligands as inhibitors of bacterial adhesion during UTI infection - 46Secretion systemsSpecialised structures secrete a wide range of substrates
7 systems identified, type VII found in mycobacteria and Staphylococcus
Transport proteins across OM or through both IM and OM - 47T3SS structureTranslocon- 3 proteins
Needle - single protein
Basal body
Cytoplasmic sorting platform
Allows secretion of substrates across 3 membranes - 48T3SS role in: Shigella Salmonella EHEC Yersinia Chlamydia PseudomonasCell entry
Cell entry/replication
Attachment
Anti-phagocytic
Replication
Entry
T3SS are widely distributed in GN bacterial pathogens - 49Toxin definitionFactors which poison/intoxicate host cells
- kill them
- alter their function
Some secreted toxins target other bacteria and host cells - 50ExotoxinsFiltrate
Secreted proteinaceous toxins - 51EndotoxinsCell-associated
LPS - 52Can toxins be entirely responsible for pathogenesisCan reproduce disease only by injection of toxin
Mutant lacking toxin is entirely attenuated
Antitoxin: vaccine or therapy - 53Toxin classificationA. Superantigens
E.g. TSST-1
B. Pore forming toxins (multimeric rings insert into membranes)
E.g. anthracis lethal toxin
C. AB toxins - shared mechanism of entry, different biochemical function: G protein modifiers (e.g, cholera toxin), translation inhibitors (e.g. Shiga toxin), proteases (e.g. neurotoxins)
D. Toxins secreted by T3SS
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- FHS Part I Immunology and Microbiology FlashCards sobre Bacterial form and function, criado por Eleanor Smith em 15-09-2020.
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- Eleanor Smith
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