Exposure and Host Adaptation Flashcards
What are the six steps to become a pathogen
- Exposure (pre infection), surviving in the environment
- Adherence, attaching to host cells and colonizing
- Cell innovations and immune evasion, persist in the host
- multiply in the host, bacterial growth
- toxicity and invasiveness disseminate, spread or invade distant sites, within or between hosts
- produce symptoms of disease, microbe induced and host response induced
How are people exposed to pathogens
some pathogens move from host to host (person to person transmission) and some are unable to survive outside of hosts for extended periods of time
STDs and other blood or bodily fluid transmission by, Neisseria gonorrhoeae, Chlamydia trachomatis, and Treponema palladium
some pathogens are able to survive outside the host in the environment
What must pathogens cope with while surviving in the environment
being eating by eukaryotes, prokaryotes, or phages
exposure to noxious chemicals, human and bio made
lack of nutrients, nutrients aren’t everywhere
exposure to sunlight and weather extremes, lack of adherence sites and UV exposure causing mutations and death
What are pathogen survival strategies for pathogens in the environment
endospores
desiccation tolerance
secondary metabolites (bacteriocins)
efflux pumps against disinfectants and antibiotics
metabolic diversity so they can grow on diverse substrates
biofilm formation
motility
What are endospores, what are they resistant to, what type of bacteria are they common in
a dormant bacterial structure that is coated in thick layers of peptidoglycan
usually form in a response to lack of nutrients
survive desiccation because of cortex area that contains the nucleic acid that is metabolically inert
UV and heat resistance
can survive millions of years, some were found in mummies in egypt
some gram + such as Bacillus and Clostridia
What is desiccation tolerance
limit protein oxidation ROS/SOD example
limit DNA damage during dehydration
membrane phospholipid adaptation, increases in saturated fatty acids, increase of cis-trans isomerization, and increase in the proportion of negatively charged phospholipids these all help hold onto water
a pathogen might encounter this is they end up on an empty hospital bed and try to stay alive
What are the four steps of biofilm formation
- Adhesion: finding a home usually formed at the air liquid layer
- Aggregation: secreting extracellular matrix/glycocalyx (polymeric matrix outside cell) and becoming 3D
- Maturation: forming the film
- Dispersal: continuous release of new microbes
active cells proliferated around the outside of the biofilm and dead cells are in the middle, the dead cells provide DNA and nutrients to the living cells
polysaccharide coat on the outside of the biofilm
channels inside the biofilm to get rid of waste products and receive nutrients inside the biofilm
What are bacteria living inside of biofilms resistant to
phagocytosis: predators or phagocytosis, the biofilm is too big for a phagocyte to consume
antibiotics: 100 fold less effective in a biofilm, diffusion rates through the biofilms are limited, metabolically the bacteria in the middle are not susceptible, antibiotics ONLY effect bacteria that are activity dividing
mechanical displacement: its hard to mechanically remove biofilms from tissues think of how hard it is to scrap biofilms off teeth, usually requires surgical removal
When are antibiotics not efficient against bacteria
antibiotics ONLY effect bacteria that are ACTIVELY dividing
this is why antibiotics aren’t as effective against bacteria in biofilms or bacteria that divide very slowly
How are bacteria motile and why is it advantageous for bacteria to be motile
use a flagella, spirochetes, for motility and chemotaxis
to help bacteria find food and survive conditions inside and outside the hosts
What types of bacteria mainly make flagellas
gram - mainly make flagella
some gram + do too
What are spirochetes
What bacteria have them
corkscrew shaped internal flagella it is in the periplamsic space between the inner and outer membrane
the flagella never sees the outside world so antibody responses are nullified and TLR 5 cannot detect (innate)
Rotation causes twisting of bacterial shape its like one big corkscrew propeller
Treponema pallidum which causes Syphilis
Borrelia burgdorferi which causes Lyme Disease
When a bacteria goes to colonize a host what are the two main barriers they must overcome
- cross primary barriers such as skin and mucosa
How do bacteria penetrate the skin
there are no known pathogenic bacteria that can penetrate the skin without help
bacteria can use an arthropod as a vector
bacteria are opportunists that wait for the skin to be bypassed in some way
Can any know bacteria penetrate the skin
no
What are the known arthropods that are used as vectors
Borrelia burgdorferi causes lyme disease and is carried by ticks
Yersina pestis causes the bubonic plague and is carried by fleas
Virures use mosquios to carry west nile fever, yellow fever, dengue fever and malaria
Plasmodium spp is a protist that uses mosquitos to transit malaria
What are ways that the skin is bypassed by opportunistic bacteria
cuts, surgery, catheters, burns, etc
IV: staphepidermis takes advantage of the breached surface
Recap of the Mucosal defense
mucus is highly effective at preventing microbes from reaching the surface fo the underlying epithelial cells
vicious, sticky substance filled with anti microbial peptides
defensins, lysozyme, slgA, lactoferrin, lactoperoxidase
traps bacteria, kills bacteria, and is resistant to degradation by enzymatic attacks
Why is GALT a liability in humans
some bacteria exploit the M cells to pass through the epithelial layer and enter the body
bacteria avoid mucus and go for the M cell where antigenic sampling occurs by transferring it to the phagocyte and the bacteria can pass through the epithelial layer
What bacteria use M cells to bypass the epithelial layer and enter the body
Salmonella enterica
Yersinia pseudotuberculosis
How do bacteria penetrate or evade the mucin defenses
GALT and M cells
using flagella to move and out of
degrade slugs
How to bacteria move away from mucus and what is a bacteria that does this
with motility methods
Helicobacter pylori uses a flagella to move through the mucus layer that has a more neutral pH than the above stomach acid which has a more acidic, lower pH
How do bacteria avoid slgAs
slgAs have an antigen binding domain and the Fc region has a docking point on the mucin to neutralize the activity of the bacteria
bacteria can produce enzymes to break apart slgAs these enzymes are slgA proteases
we have slgA1 and slgA2 pathogens can degrade igA1 sot they think that our bodies formed IgA2 which cannot be degraded by pathogens
What is the common type of host produced natural antibodies in humans
defensins
what are defensins
cationic (positively charged) peptides that bind to the negatively charged surface of bacteria and disrupt the bacterial membranes
How do bacteria combat defensins, four main ways
bacteria try to make their membrane surface more positively charged so the defensins that are positively charged are not attracted to them
LPS and LTA modification to change the net negative charge, become more positive to not attract defensins
they can make a capsule to protect their membrane, the thick polysaccharide layer protects the bacteria by slowing or preventing defensin diffusion through
microbial proteases can degrade defensins, not allowing the defensins to disrupt the membrane
counteract defensin channels by using cytoplasmic proteins to ‘plug the hole’ that is formed by defensins in the bacterial membrane
What is the main nutrient required by bacteria to proliferate, which bacteria does not use this and what does it use
many, but not all, pathogens require iron to proliferate
Borrelia burgodorferi uses Mn2+ lyme disease
free iron is often a limiting factor for growth 10^-18 M of free iron inside the body, so not a lot at all
How much free iron is in the body, where is the other iron found
10^-18 M of free iron in the body
almost all iron is bound to a protein this is chelated
considered antimicrobial peptides “nutritional immunity”
Lactoferrin Transferrin Ferritin Heme Siderocalin
Where is Lactoferrin found in the body and what is its role
mucosal sites and its present in neutrophil granules
has a high affinity for iron so it takes up iron before pathogens can when inside of mucosal sites and around neutrophil granules
Where is Transferrin found and what is its role
in the blood serum, induced by IL-6 and produced by the liver
deliver iron from absorption centers in the duodenum and white blood cell macrophages to all tissues
Where is Ferritin found and what is its role
intercellular iron storage
30% of bound iron in the body
Where is Heme found and what is its role
Hemoglobin
70% of the bodies iron
What are siderocalins
siderocalins interfere with the function of bacterial siderophores
the anti siderophore
we produce siderocalins to take away the bacterial siderophore
Iron in the body is highly controlled within the host so how does bacteria get it from the host
compete with the host via siderophores or steal the iron
What are siderophores and what are the two primary structural groups
low molecular weight compounds that chelate iron with very high affinities
they take a lot of work for bacteria to make them
caterchols: enterbactin have very high affinity for iron and is produced by bacteria, this takes a lot of enzymatic processes to form and can bind to iron better than our host defenses, it outcompetes the host
hydroxamates: angulibactin bind iron with affinity that competes with host iron binding but not as good as catechols
What are other ways that bacteria can get iron without producing siderophores
take other bacterias siderophores: easier than making their own
simply steal the hosts iron-chelators: directly take up transferrin, lactoferrin, or heme: they can destroy the protein in the hosts cytoplasms and release the iron for their own use
produce toxins such as hemolysis and other cytolysins that destroy host cells and release their iron stores (ferritin, the intracellular iron storage protein)
What are gram + strategies for iron acquisition
they can make two siderophores: Staphyloferrin A and Staphyloferrin B they both have binding proteins that bind to iron and push it through a complex below into the bacterial cell for use, this requires ATP
best way to get iron by them is to strip the heme away from the host cell through a complex, staph, strep, listeria
What are gram - strategies for iron acquisition
they have transferrin and lactoferrin binding proteins along with a hemopore that can bind and uptake hemoglobin through the membrane
they also have two different siderophores one that uses an outer membrane receptor and not that uses TBDT (transmembrane protein)
What are stealth siderophores
bacteria take their siderophore and coated it in glucose to make it appear different and make it less recognizable by the hosts siderocalin, therefore the siderocalin cannot bind to stealth siderophores
there is an evolutionary tug of war between hosts and bacteria with siderophores and siderocalins
What are key detemerinants of bacterial adhesion inside of hosts
pili and fimbriae are key parts of binding to cells and tissues inside hosts
What are the different ways bacteria can adhere to cells and tissues
pili/fimbriae: these are interchangeable
surface adhesions
MSCRAMMS
if you can block attachment you can block infection
What are MSCRAMMS, what bacteria uses MSCRAMMS
Microbial surface components recognizing adhesive matrix molecules
type of adhesion uses by Staphlyococcus aureus
not the same as pili and fimbriae
What is the difference between pili and fimbriae
interchangeable terms
pili: generally refers to longer, thicker surface structures
fimbriae: generally refers to shorter, thinner structures
the best understood mechanism of adherence is the attachment of bacteria to the hosts through rod-shaped filamentous structures
first identified in gram - but more recently they also appear prevalent in gram +
pili come in a variety of shapes and types, there are over 30 types identified for E. Coli alone
How is tissue tropism governed by pili
by the piling tip, this establishes the contact between the host and the bacterial surface
contributes to the host-cell or tissue-specificity of the pathogen
some pathogens can interchange the piling tip but keep the same shaft
What do UPEC strains of E. coli P Pili attach to
attaches to the mannose sugars on the bladder epithelium
idea to put mannose sugars in the bladder to try and get pili of E. coli to bind to that instead of the epithelium on the bladder
What are the three types of pili
P Pili
Type IV or Bundle forming pili (BFP)
Curli Pili
How are Type I Fimbriae aka P Pili formed
by chaperone-usher pathway
holds onto the proton with a beta strand to help with stability while it is being moved this beta strand is called the donor chaperone strand
assembly is the tip going out list and then slowly pushes it out
This occurs in the periplasm
Fim C is the donor chaperone strand
chaperone never becomes part of the pili, just helps stability?
What type of pili are formed by the chaperone-usher pathway
Type I fimbriae and P. pili
How are curli pili formed
CsgE, F, G dependent assembly, after secretion past outer membrane, pilin subunit CsgA self-polymerizes
CsgD is a transcription factor that regulates expression of the csgBAC operon
CsgC is a chaperone that escorts it to the outer membrane that is located in the periplasmic space, secreted as it self polymerize
Csg: curli specific genes
How are type IV aka bundle forming pili formed
secretion dependent
monomers in the inner membrane protrude out the cell surface
stable protein protein interactions work to assemble it
to retract they do the opposite, its pulled back through the same opening
What type of pili do Neisseria gonorrhoeae use
type IV bundle forming pili
What type of pili do E. coli use
type I aka P pili and curli pili
What types of pili are found in both E. coli and Salmonella spp.
Curli fibers
What are the csg in E. Coli
csgBAC and csgDEFG
What are the csg in Salmonella
curli specific genes
afg: aggregative fimbriae
agfBAC and agfDEFG
Agf: aggregative fimbriae which promotes the aggregation between bacteria, more bacteria bacteria interaction but still impacts the host
What are the pili of gram + bacteria like
important for biofilm formation and in pathogenic strains: adhesion and invasion
pilin subunits are covalently attached to each other and to the peptiodogylcan layer by enzymes called sortases
What are sortases
pilin subunits are covalently attached to each other and to the peptiodogylcan layer by enzymes called sortases in gram + pili
sortases recognize sequence motifs in their substrates LPXTG to cleave the substrate at the threonine residue
this cleaved substrate is coupled to pepitdoglycan or the next available pilin subunit through a second sequence motif YPKN
all the pilin subunits will have this signature at the C-terminus and this links it to another monomer or the cell wall itself
How are pili assembled in gram + bacteria
sortase is how everything can get through the cell wall
What are non-fimbrial adhesions of gram + bacteria
hair-like protrusions that resemble pili
many of them bind to extracellular matrix and connective tissue such as fibronectin, collagen, fibrinogen, vitronectin, laminin = MSCRAMMs
What does Streptococcus pyogenes use to bind to cells
gram + bacteria
nonfimbrial adhesion
F protein binds Fibronectin
pilus-like structures made of M protein that binds to factor H
binds factor H, destroying C3 convertase and avoiding C3b opsonization: this is complement and phagocytosis avoidance
has a sortase to bind to cell wall
What are afimbrial adhesions
InIA and InIB of listeria monocytogenes triggers bacterial uptake by host cells
causes actin cytoskeleton of host cell to rearrange and allow internalization
To maintain a persistent infection and to be a successful pathogen what must happen
the pathogen must be able to combat the immune defenses of the host
the innate and adaptive immunity
innate: complement and phagocytosis
adaptive: antibodies/phagocytosis and CTLs
How do bacteria use capsules to avoid complement
prevent alternative pathway activation
inhibits formation of the C3 converts binds serum protein H rather than factor B
steric hindrance is used by the capsule to prevent phagocytosis
factor H and protease I inactive C3b prevent the complement in our own tissues
How do capsules avoid complement
prevent alternative activation: inhibits formation of the C3 convertase by binding factor H instead of factor B and this inhibits phagocytosis
prevents formation of the MAC complex: proteins are unable too get through the capsule of the membrane, this prevent direct lysis
How do bacteria use host mimicry
make capsules out of sialic or hyaluronic acid
What is sialic acid and how is it used by bacteria
found in relatively high amounts in all animal tissues
prevents comment
the sialic acid is used by bacteria in host mimicry, they make capsules out of it to avoid detection by the host immune system
What is Hyaluronic acid and how is it used by bacteria, what bacteria is an example of it
found as glycosaminoglycan found in connective, epithelial, and neural tissue
make capsules out of hyaluronic acid in bacterial host mimicry
streptococcus pyogenes
What is the role of C5a peptidase/toxins
secrete enzymes (proteases) that destroy the complement proteins, C5a for instance by some gram +, then the neutrophils don’t know where to attach to
produce toxins that kill, inactivate, immobilize, or reduce the strength of immune cells such as phagocytes they can also prevent cytokine signaling
What do pathogens avoid if they become intracellular
pathogens that live inside the host cells are not directly exposed to the immune system
no antibodies no complement proteins no defensins no lysozyme no phagocytes no direct exposure to any immune cells really advantageous if you can survive inside a macrophage
they could also escape the phagosomes into the cytoplasm before the bacteria are killed, they produce toxins that disrupt, degrade, or make holes in the hosts membrane
How do bacteria escape the phagosome
alternatively bacteria just escape from the phagosome into the cytoplasm before the bacteria are killed
they produce toxins that disrupts, degrade, or make holes in the hosts membrane
What kind of bacteria lyse the phagosome
Listeria monocytogenes produces a pore forming hemolysin called listeriolysin O LLO
only active at pH 5.5 as phagosome becomes acidified and it escapes
PlcA result in the lysis of the phagosome membrane
vacuole is lysed and bacteria escapes into cytosol and replicates
What is actin-based motility of bacteria and what bacteria use this
many pathogens that can direct their own endocytosis and can also manipulate the actin cytoskeleton once inside the host cell
use actin-based motility
able to push themselves around the cell and into neighboring cells
never have to leave the intracellular enivrionemt Listeria monocytogenes Shigella flexneria (dysentary) Rickettsia rickettsii (Rocky Mtn Spotted Fever)
don’t every have to exit the cell
cytotoxic T lymphocytes can enter the cell, but this results in inflammation
How does Listeria monocytogenes move pithing and between cells
uses actin-based motility
How does Legionella pneumophilia avoid phagolysosomal fusion
removes proteins necessary for membrane fusion from phagosome, LAMP-1 and LAMP -2
- Legionella is taken up inside the cell
- the phagosome does not become acidified because it does not fuse with the lysosome
- phagosome surrounded by the endoplasmic reticulum studded with ribosomes
- bacteria multiply in phagosome
- phagosome ruptures
- host cell lyses and bacteria escape
How does Salmonella Typhimurium prevent phagolysomal fusion?
hijacks cell’s actin cytoskeleton to create its own space and make its own vesicle called the SCV the salmonella containing vesicles
- bacteria trigger actin rearrangements on the surface of the cell, ruffling occurs and ruffles grow into pseudopods
- pseudopods encircle and engulf bacteria and the bacteria are taken up into spacious vacuoles
- bacteria remodel the vacuoles creating a growth-conducive environment and the bacteria replicate in the vacuoles
How does Mycobacterium tuberculosis prevent phagolysomal fusion
uses host protein TACO to coat the phagosome
- bacteria bind CR3 on surface of macrophage and the bacteria are taken up in a vesicle
- bacteria recruit host protein to surface of phagosome, no fusion of lysosome with phagosome
- bacteria prevent endocytic acidification, have reduced bacterial oxidative burst, and bacteria can replicate
How does Brucella abortus prevent phagolysomal fusion
only replicates upon acidification of vacuole directing it to the ER
- Brucella abortus enters the cell and binds and fuses with the lysosome
- prefers fusion with the lysosome and the acidification processionals and then it gets sent to the ER to escape from the cell
How does Chlamydia replicate inside the cell
- Chlamydia enters the cell in EB form (non-replicative form)
- EB changes into RB form (replicative form)
- RBs replicate and some stay RB and others switch back to EBs
- EBs are released from the cell to go infect other cells
How does Coxiella replicate inside the cell
promotes replication upon acidification
- Coxiella enters the cell in the SCV form (non-replicative form)
- SCV fuses with the lysosome
- this fusion changes it to LCV and this is the replicative form producing SCVs and LCVs
- the SCVs are released from the cell to go infect other cells
How do bacteria resist reactive oxygen species ROE’s, what is an example of a bacteria that does this
reactive oxygen species are the primary way the oxidative burst kills bacteria
produce enzymes that neutralize oxygen radicals
catalase H2O2 –> O2 + H2O
superoxide dismutase O2- –> O2+H2O2
Salmonella SodCl enzyme is phage encoded
What type of bacteria can avoid nitric oxide (reactive nitrogen compound)
Neisseria meningitidis produces nitric oxide reductase that converts NO to N2O (laughing gas) which is less toxic
E. Coli uses nitric oxide dioxygenase to convert NO to NO3- (nitrate)
How does Streptococcus pygoenes cope with the adaptive immune system
uses protein G
uses it as a surface domain to bind the antibody backwards and not identify the bacterial cell
How does Staphylococcus aureus cope with the adaptive immune system
uses protein A
bind to the Fc regions of antibodies specifically IgG
coat the antibodies which face outwards
surface domain that binds the antibody backwards
What are all the ways that bacteria can cope with the adaptive immune response
protein G
protein A
Collagen/fibronectin/fibrinogen which are ECM proteins, clumping factors bind fibrinogen
host mimicry: bind host collagen they can entirely coat their surfaces, host views it as self and doesn’t emit an immune response
What are the ways that bacteria can spread cell to cell into new parts of the body
actin based motility
flagella or chemotaxis
breakdown pus
secrete spreading factors that break down connective tissue and ECM
secrete blood thinners to escape from blood clots
want to move to different parts of the body so they are harder to find by the immune system and to disseminate through the body
How do bacteria breakdown pus, what is the reason for this
pus is a thick substance that tends to trap bacteria
pus is composed of proteins, dead cells and DNA, NETS hold onto bacteria while neutrophil is functioning
bacteria secrete DNases to thin it to become untapped and spread
to disseminate through the body
What is the role of bacterial spreading factors
collagenases, elastases, hyaluronidases and other proteases
break down connective tissue and extracellular matrix proteins to be able to infect different areas and move to new areas
to disseminate through the body
Why does bacteria secrete blood thinners
secrete blood thinners to degrade fibrin to escape from blood clots and spread to other parts of the body
Streptokinase degrades fibrin
to disseminate through the body
