Bacterial Adhesion on Host
Why do bacteria adhere
The host has a number of innate defenses against bacteria Skin and mucus – physical barriers Peristalsis of the gut and the
esophagus Ciliated epithelium in the respiratory
tract Flushing of bodily fluids
Bacterial adherence
Bacteria are more resistant to normal clearing mechanisms, antibiotics, bacteriolytic enzymes and immune killing when they are adhered to surfaces such as the host cell
Therefore, adhesion is essential for bacterial colonization Maintaining the normal flora in and on the host
But, it also the crucial first step in many infectious disease processes
Evidences for requirement of attachment:
Susceptibility for certain bacteria to infect specific tissue is directly proportional to its ability to adhere to that tissue.
Bacterial variants that are found to have a reduced capacity to adhere in vitro have decreased infectivity in vivo.
The bacterial binding capacity of epithelial cells from individuals prone to certain bacterial infections is sometimes higher than those tissues from uninfected individuals.
Both bacterial & tissue cell surfaces are negatively charged, it is overcome by electrostatic ( cations bridging eg. Ca++) and hydrophobic forces (Lipoteichoic acid).
Adherence prevents microorganism from flushing activity of saliva, mucous etc. , enzymes and antibodies.
It enable bacteria to deliver its product close to the cell & colonization.
Crude mechanical device &/or surface receptor molecules on the surface of protozoan and worms.
All the organism uses multiple binding sites for survival.
How do bacteria adhere to the host? Surface-expressed bacterial proteins
Microbial Surface Components Recognizing Adhesive Matrix Molecules - ECM (extracellular matrix )
Proteins with other receptors Fimbriae (or pili)
Protein fibers extending from the bacterial cell Enzymes
Bacterial enzymes can expose cryptic host cell receptors (neuraminidase, -enolase)
Biofilm formation Communities of bacteria adhering to a solid surface which
can be host tissue
Why adhere to the host ECM
The ECM is ubiquitous in the body, especially at mucosal surfaces
It is abundant (enough receptors for everybody) It is present in all vertebrates Individual components share structural
characteristics (not completely host-specific) It is differentially present in normal and diseased
tissue May signal a pathogenic opportunity
Location of Adhesions molecules
Fimbrillae of gram-positive bacteria Fimbriae of gram-negative bacteria Filamentous heamagglutinin (FHA) of
Bardetella pertussis Membrane protein of Mycoplasma of foot. Protein II of N. gonorrhoeae Capsid / envelope protein of viruses ( eg.
Heamagglutinin of influenza A virus).
Prokaryotic and Eukaryotic Interactions
Intracellular
Eukaryotic Cell
Receptor
Virulent Bacteria
Prokaryotic Cell
Control of virulence factors:(Pilin, capsule, invasins, toxins etc)
Adherence blockers
Pili or adhesins
Prokaryotic and Eukaryotic Interactions
Intracellular
Eukaryotic Cell
Receptor
Virulent Bacteria
Prokaryotic Cell
Control of virulence factors:(Pilin, capsule, invasins, toxins etc)
COLONIZATION
Adherence blockers
Pili or adhesins
Prokaryotic and Eukaryotic Interactions
Intracellular
Eukaryotic Cell
Receptor
Virulent Bacteria
Prokaryotic Cell
Control of virulence factors:(Pilin, capsule, invasins, toxins etc)
COLONIZATION INVASION
Adherence blockers
Pili or adhesins
TERMS USED TO DESCRIBE ADHERENCE FACTORS IN HOST-PARASITE INTERACTIONS
ADHERENCE FACTOR
DESCRIPTION
Adhesin A surface structure or macromolecule that binds a bacterium to a specific surface
ReceptorA complementary macromolecular binding site on a (eukaryotic) surface that binds specific adhesins or ligands
Lectin Any protein that binds to a carbohydrate
Ligand A surface molecule that exhibits specific binding to a receptor molecule on another surface
Mucous The mucopolysaccharide layer of glucosaminoglycans covering animal cell mucosal surfaces
FimbriaeFilamentous proteins on the surface of bacterial cells that may behave as adhesins for specific adherence
Common pili Same as fimbriae
Sex pilus A specialized pilus that binds mating procaryotes together for the purpose of DNA transfer
Type 1 fimbriaeFimbriae in Enterobacteriaceae which bind specifically to mannose terminated glycoproteins on eukaryotic cell surfaces
GlycocalyxA layer of exopolysaccharide fibers on the surface of bacterial cells which may be involved in adherence to a surface
CapsuleA detectable layer of polysaccharide (rarely polypeptide) on the surface of a bacterial cell which may mediate specific or nonspecific attachment
Lipopolysaccharide (LPS)A distinct cell wall component of the outer membrane of Gram-negative bacteria with the potential structural diversity to mediate specific adherence. Probably functions as an adhesin
Teichoic acids and lipoteichoic acids (LTA)
Cell wall components of Gram-positive bacteria that may be involved in nonspecific or specific adherence
specificity of adherence of bacteria to host cells or tissues Tissue tropism: particular bacteria are known to have
an apparent preference for certain tissues over others, S. mutans - dental plaque S. salivarius -epithelial cells of the tongue
Species specificity: certain pathogenic bacteria infect only certain species of animals, N. gonorrhoeae - humans; Enteropathogenic E. coli K-88 - pigs; E. coli CFA (colonizationfactor antigens) I and II – humans.
Genetic specificity within a species: certain strains or races within a species are genetically immune to a pathogen , Susceptibility to Plasmodium vivax infection (malaria) is
dependent on the presence of the Duffy antigens on the host's redblood cells.
Mechanisms of Mechanisms of Adherence to Cell Adherence to Cell or Tissue Surfacesor Tissue Surfaces
Nonspecific adherence:
Reversible attachment of the bacterium to the eukaryotic surface (sometimes called "docking") Possible interactions and forces involved are:
1. hydrophobic interactions
2. electrostatic attractions
3. atomic and molecular vibrations resulting from fluctuating dipoles of similar frequencies
4. Brownian movement
5. Recruitment (Quorum Sensing) and trapping by biofilm polymers interacting with the bacterial glycocalyx (capsule)
Specific adherence: Reversible permanent attachment of the microorganism to the
surface (sometimes called "anchoring"). Direct evidence that receptor and/or adhesin molecules mediate specificity of adherence of bacteria to host cells or tissues. These include:
1. The bacteria will bind isolated receptors or receptor analogs.
2. The isolated adhesins or adhesin analogs will bind to the eukaryotic cell surface.
3. Adhesion (of the bacterium to the eukaryotic cell surface) is inhibited by: isolated adhesin or receptor molecules adhesin or receptor analogs enzymes and chemicals that specifically destroy adhesins or
receptors antibodies specific to surface components (i.e., adhesins or
receptors)
SPECIFIC ATTACHMENTS OF BACTERIA TO HOST CELL OR TISSUE SURFACES
Bacterium Adhesin Receptor Attachment site Disease
Streptococcus pyogenes
Protein FAmino terminus of fibronectin
Pharyngeal epithelium
Sore throat
Streptococcus mutans
Glycosyl transferase
Salivary glycoprotein Pellicle of tooth Dental caries
Streptococcus salivarius
Lipoteichoic acid
Unknown Buccal epithelium of tongue
None
Streptococcus pneumoniae
Cell-bound protein
N-acetylhexosamine-galactose disaccharide
Mucosal epithelium pneumonia
Staphylococcus aureus
Cell-bound protein
Amino terminus of fibronectin
Mucosal epithelium Various
Neisseria gonorrhoeae
N-methylphenyl- alanine pili
Glucosamine-galactose carbohydrate
Urethral/cervical epithelium
Gonorrhea
Adhesion Mechanism
gram negative bacteria
Types of bacterial secretion used by gram
negative bacteria
Type III Secretion System A cylindrical base, similar to the flagellar
hook-basal body complex, spans the periplasm and is associated with the two bacterial membranes where ring-like structures are detected, ensuring stabilization of the whole structure upon the bacterial cell envelope. An elongated hollow extracellular structure called the needle extends around 50 nm outside the bacterial cell wall (it varies according to the different bacterial species) and can be inserted into eukaryotic membranes. Energy derived from ATP hydrolysis drives translocation of bacterial proteins (known as TTSS effectors) from the bacterial cytoplasm to the eukaryotic cell cytoplasm, where they can hijack host signaling pathways.
Tir (translocated intimin receptor),/Intimin Interaction EPEC, the bacteria provides both
the ligand and the receptor, via its type III secretion system (TTSS), injects into the cytosol of target cells the protein Tir, which integrates into the host-cell plasma membrane, dimerizes, and functions as a receptor for the bacterial outer membrane intimin. Tir/intimin interaction promotes Tir phosphorylation by Fyn and Abl ( Host Kinase), inducing the recruitment of the protein adaptor Nck, which in turn recruits N-WASP (Wiskott-Aldrich syndrome protein) and the Arp2/3 complex (actin-related protein 2/3), leading to actin polymerization and the formation of structures known as pedestals. Actin binding proteins such as talin are recruited to the pedestal, stabilizing the structure.
Adhesion Mechanism
gram positive bacteria
MSCRAMMS
Microbial Surface Components Recognizing Adhesive Matrix Molecules
S. aureus adhesion to fibronectin and collagen binding was described in the early-mid 1980s
The first MSCRAMM was cloned and characterized in 1992 – Cna (collagen adhesin)
Most (all) Gram positive pathogens and commensals have ECM-binding MSCRAMMs
Many non-pathogenic Gram positives do not have MSCRAMMS E.g., truly environmental bacteria
MSCRAMM domain structure
Gram positive MSCRAMMs have a number of unique features
MSCRAMMs are anchored into the cell wall Surface exposed
The proteins must have – Signal sequence for secretion by the generalized Sec
pathway Cell wall anchor sequence for insertion into the cell wall by
sortase ECM binding domains, which will depend on the type of
ECM bound (may have one or more)
Collagen binding MSCRAMMs
Cna – S. aureus CbpA – A. pyogenes CpCna – C. perfringens Ace – E. faecalis Acm – E. faecium Cne – S. equi Cpa – S. pyogenes Other Gram positive bacteria bind collagen, but the
genes responsible have not been identified
Collagen binding MSCRAMM domain structure
N-terminal signal sequence and C-terminal cell wall anchor
A domain Contains the collagen binding domains
B domains 1-4 repeated domains ~80-200aa long (60-100% aa identity)
Signal Signal sequencesequence
A domainA domain B domainsB domains Cell wall Cell wall anchoranchor
Cna – A domain
The structure of the collagen‑binding A domain (green) contains a trench similar to that seen in the collagen binding domain of 1 family integrins
The orange lines represent the collagen triple helix
Cna – B domains
The number of B domains in a collagen binding protein varies from strain to strain This is the case for collagen binding proteins
from different bacteria Modeling studies show that B domains
pack in a zig-zag fashion They may expand and contract from the
bacterial cell wall and so aid in the projection of the A domain away from the cell surface
Specificity
Although all collagen types are unique, there is some structural conservation between some of the types
Most collagen adhesins bind preferentially to one/two types Higher affinity binding
However, many collagen adhesins will bind to more than one type of collagen
Most collagen adhesins require the collagen structure to be intact for binding to occur
CpCna
A collagen binding protein of C. perfringens Binds type I collagen (only type tested so far)
Only plasmid-encoded MSCRAMM known Immediately adjacent to the cna gene is a
gene encoding sortase Only shares 15.4% amino acid identity and
35.2% similarity to Cna from S. aureus
Role of collagen binding in disease
Cna – osteomyelitis, endocarditis In mice were infected IV with wildtype S. aureus or a cna
knockout (model of hematogenous osteomyelitis) 70% of mice infected with wildtype S. aureus had osteomyelitis
in the hind leg vs. 5% of mice infected with the cna knockout Rats with surgically traumatized heart valve (model of
endocarditis) were infected with wildtype S. aureus or a cna knockout
The wildtype adhered better than the cna knockout When both wildtype and cna knockout were co-administered,
the wildtype out-competes the mutant
Role of collagen binding in disease
CbpA – osteomyelitis (?) 100% of A. pyogenes osteomyelitis isolates (n=5)
carry cbpA In contrast, only 48% of all A. pyogenes isolates
(n=75) carry this gene Ace – periodontal disease (?)
Wildtype E. faecalis adheres to exposed tooth roots (dentin – collagen type I) better than an ace knockout
Fibronectin binding MSCRAMMs
SfbI (PrtF1), F2 (PFBP), M1 and M3 proteins, Fbp54, Fba, FbaB - S. pyogenes
ScpB - S. agalactiae FnBB – S. dysgalactiae FNE, FNZ, SFS – S. equi FnbpA, FnbpB - S. aureus Similarly, a number of other bacteria bind
fibronectin, but the genes involved have not been characterized
SbfI binding to fibronectin
Best studied fibronectin adhesin of S. pyogenes Binds to fibronectin through two domains
C-terminal repeat region – fibrin binding domain Non-repetitive domain UR – collagen binding domain
Binding through these two domains is important for subsequent invasion
S. pyogenes SfBI protein
SfBI can also “recruit” collagen type I or IV via pre-bound fibronectin
This enables the bacteria to form collagen-coated aggregates and allows the bacteria to adhere to the collagen matrix (without having a collagen adhesin)
S. aureus FnbpA and FnbpB
Most isolates express these related proteins encoded by linked genes
These proteins bind the N-terminus of fibronectin by their C-terminal repeats, in a similar manner to that of SfbI
These proteins also bind to fibrinogen and elastin Both proteins can adhere to platelets, but only FnbpA
can aggregate them
Fibrinogen binding MSCRAMMs Clumping factor A and B (ClfA, ClfB) – S.
aureus FnbpA and B – S. aureus also binds
fibrinogen Fbe – S. epidermidis FbsA and FbsB – S. agalactiae
Fibrinogen binding MSCRAMM domain structure
A: Fibrinogen binding domain R: Serine-aspartate repeat region; forms a stalk ClfA and ClfB have an identical domain structure Fibrinogen binding proteins appear to have a less complex domain structure
compared with fibronectin and collagen binding proteins
Signal Signal sequencesequence
A domainA domain R domainR domain Cell wall Cell wall anchoranchor
S. aureus ClfA and ClfB
Enables S. aureus to clump in the presence of fibrinogen – hence the name
Allows S. aureus to adhere to fibrinogen-containing substrates such as plaques in blood vessels
For ClfA, fibrinogen binding occurs through binding of the A domain to the chain of fibrinogen
For ClfB, binding is through the and chains ClfB also binds cytokeratin
Thought to be important in nasal colonization
Fibrinogen binding in disease
S. aureus is an important cause of infective endocarditis in patients without a history of prior heart valve damage S. aureus uses ClfA to coat itself with fibrinogen The fibrinogen-coated bacteria engage resting platelet
glycoprotein GPIIb/IIIa and anti-ClfA antibodies Subsequent signal transduction leads to activation of
GPIIb/IIIa and aggregation of platelets A clfA- mutant has reduced virulence in a rat model of
endocarditis Also, L. lactis strains expressing ClfA can adhere to heart
tissue
Once bacteria are successfully attached to the host they have limited options
They can remained attached, but will eventually become displaced when host cells turn over Gut - 1-2 days Most other mucous membranes - 5-7 days
Bacteria can reattach to a new host cell, but they are still at the mercy of host specific and innate defenses
This is not a problem for commensal bacteria
Downstream regulation
Bacteria can invade into the host cell Requires both interaction of bacteria with host cell
molecule(s) AND reorganization of host cytoskeletan Bacteria can invade into healthy cells However, tissue damage through trauma,
inflammation and/or other microbial infections can expose “different” tissue for the bacteria to adhere to and subsequently invade
For this to occur, bacteria may need additional adhesins
Linking adhesion to invasion
Binding of the SfbI repeat region to the N-terminal fibrin-binding domain of fibronectin co-operatively activates the adjacent SfbI UR domain to bind the fibronectin collagen binding domain
The repeat region of SfbI mediates adherence and constitutes a prerequisite for subsequent invasion
The SfbI UR domain efficiently triggers invasion into host cells
Prophylactic potential of MSCRAMMs
Due to increasing antibiotic resistance, we need novel methods for disease prophylaxis and/or treatment
Anti-adhesion therapy and immunity can: Preventing adhesion of the bacteria with a vaccine Reversing adhesion of the bacteria with an agonist
The major drawback is that most bacteria have multiple mechanisms for host cell adhesion
It may be necessary to use multiple agents or a broadly-effective agent
Receptor analogs - adhesion agonists
Bacteria that lack adhesins are swept away
In the presence of adhesion agonists, bacteria are no longer able to bind
Adhesion agonists
This approach has been successful with pathogens that bind via carbohydrate-specific adhesins
The agonist is structurally similar to the glycoprotein or glycolipid receptor
There have been few clinical trials that have shown efficacy of adhesion agonist therapy
However, drinking cranberry juice (which contains mannose) can - Displace uropathogenic E. coli from the urinary tract
epithelium preventing bladder infections Reduce colonization by S. mutans, a cause of dental caries
Passive protection
Aurexis® Humanized monoclonal antibody against ClfA For treatment of S. aureus bacteremia in adults Completed Phase II trials in 2005 Is proceeding into Phase III testing No more information is available
Vaccines
Antibody binding to the MSCRAMM should block binding to the ECM receptor
With multi-factorial adhesion, it may not be possible to prevent all infections
However, by targeting specific MSCRAMMs, such as collagen binding proteins, it may be possible to prevent specific diseases Osteomyelitis, septic arthritis Periodontal disease
Experimental MSCRAMM vaccines FnbpA and ClfA vaccination to prevent mastitis
DNA vaccine was administered to dairy cattle with S. aureus challenge
Vaccinates had a 50% reduction in number of mastitis infections compared with non-vaccinated controls
IN vaccination with Sfb1 of S. pyogenes protects against IN challenge, but not SC challenge SC challenge by-passes the need to adhere May not be a good model for skin infections
Immunization with a fibronectin binding protein of S. equi prevents a strangles in a mouse model Vaccinated horses have good antibody responses
How do MSCRAMM antibodies work?
Opsonization of bacteria for PMN-macrophage ingestion and killing
The role of complement-mediated killing may also be involved
However, it is still unclear to what extent inhibition of bacterial adhesion contributes to the in vivo prophylactic or therapeutic effect
Top Related