Bacteriology Flashcards
Human microbe
we are massively outnumbered by microbes (bacterial microbes); harmless
Pathogen
pathogen that can cause disease; it wants to; wants to gain access to nutrients so it can reproduce
Infection
when microbes enter the host and multiplies
Disease
microbial infection damages host (if multiplying so slowly doesn’t cause diseases; so sometimes infections lead to disease and sometimes not)
Pathogenicity
ability of an organism to cause disease; how pathogenic a microorganism is depends on their virulence factors (ex: plasmids)
Virulence
the extent to which a pathogen can cause disease; bad pathogen = one that causes severe disease (bad for us and pathogen); if pathogen kills host, before it can find a new host (transmission) = bad pathogen! It will die with us or sit in our body where no nutrients coming in ; can really only transmit pathogens when showing symptoms (contact, sneezing, etc.)
Opportunistic pathogen
only get you when you have a compromised immune system, weak, dysbiosis, etc.
Opportunistic conditions
- compromised immune system (immunodeficiency)
- disruption in the balance of normal microbes
Obligate pathogen
pathogens must cause disease to be transmitted (no such thing as non-virulent strain of this bacteria or asymptomatic) ; causes disease and that’s it
Facultative pathogen
can cause disease but do not require a host to complete the life cycle; can cause disease in a healthy host but they can also leave outside of a host like Cholera (lives in fresh water, when it gets access to you - causes disease)
Cystic Fibrosis
disease in lungs where it’s not producing right consistency of mucous; collects in lungs and too heavy or too sticky to clear so Pseudomonas can stick and cause disease
Why is Pseudomonas aeruginosa a successful pathogen?
- natural habitat is ubiquitous; found almost anywhere; in soil, water, and healthy people
- metabolism: very diverse; aerobic and anaerobic resp (NOT a form of fermentation; uses resp chain)
- can metabolize (can grow off of) 75 different carbon compounds or foodstuffs
- has a big genome and can grow everywhere)
- minimal nutrition needs ; can still thrive in near starving conditions
- grows in wide variety of temps; so no optimal temp ; always there!
- resistant to high salt and often grows in biofilms
- no sweeping antibiotic resistance; but growing + genetic mutations and associations with biofilms has allowed treatment resistance
Louis Pasteur
Cells come from pre-existing cells
Bubonic plague
macrophages carrying the bacteria migrates to lymph nodes to report back to central command of antigen its found but bacteria reproduce and lyse the macrophage that causes the bubos (pustules of plague) - to explode lymph nodes – pustules that form on skin
Robert Koch
- studied the theory that microorganisms cause human disease
- showed the cause and effect relationship between pathogen and disease
Koch’s Postulates
Pathogen must :
- be present in all cases of the disease (to ensure it’s that and nothing else)
- must be able to be grown in pure culture (unfortunately we haven’t caught up with yet bc lots of pathogens cant be)
- cause disease from pure cultures (MICE)
- be able to be re-isolated
T or F. Stress dampens immune response
T!
Steps to establishment of infection
- pathogen exposure (ex: Yersinia is highly virulent but we just aren’t exposed in western world)
- host adherence (has to stick to us)
- invasion: must gain entry; not good enough to just sit on cells
- evade immune system to cause host damage to colonize and grow
○ requires evasion of immune system (adaptive, etc.); must breach innate barrier first - host cell damage (in order to cause disease = toxin secretion or induce apoptosis)
Example of a loose/transient adhesion
things that infect resp. tract bc it sticks to mucus of lungs but we have way to clear that mucus out
Most often, adhesion is promoted by virulence factors
proteins usually
One of the fastest way to cause disease in a host
Toxin secretion
Virulence factors
properties of pathogen that aid infection; can be proteins other chemical conditions (acid tolerance for ex)
Fimbriae
involved in attachment to host cell and surfaces; usually very specific (host range .. only attach to things it can recognize)
Capsule
collection of glycoproteins and glycolipids = creates a sticky slime = adherence; also chemical barrier to prevent antibiotics from getting in (evasion and adherence)
NAG
- monosaccharide derivative of glucose
- it is an amide between glucosamine and acetic acid
NAM
- a monosaccharide derivative of NAM (the ether of lactic acid and NAM)
Oligo-
less than 30 AAs
Peptidoglycan of Neisseria gonorrhea
extensively crosslinked (evolved); they saturate the cell walls to be resistant to antibiotics targeting cell walls
Penicillin
inhibits formation of cross-linking (bundling of peptidoglycan fibres)
Lysozyme
cleave peptidoglycan crosslinks
LPS
- major component of the OM of gram -
- elicit strong immune responses
- LPS contribute greatly to structural integrity of bacteria and protecting the membrane from chemical attacks
- also increases negative charge of cell membrane and helps stabilize overall membrane structure
antigenic
elicits a strong immune response
T or F. Core and O antigen are essential, whereas lipid A is non-essential
F! Lipid A is essential and the core and O antigen are non-essential
Lipid A
phosphorylated glucosamine disaccharide ; associated fatty acids - allow bilayer formation (amphipathic); usually 6 acyl chains (highly antigenic)
The core of LPS
- attaches directly to the lipid A; mostly sugar but can contain amino acids
- very diverse
- Kdo units = most common sugar; forms “inner core”
The O antigen of LPS
Attached to core oligosaccharide; highly diverse (forms serotypes); recognized by immune system - antigenic
This makes a bacterial cell wall appear smooth
O antigen;
degree of covalent additions (on O antigen) to lipid A is characteristic of different strains
Rough LPS
we see bacteria with the rough LPS are often less virulent (less variability); less resistant, more sensitive to antibiotics
Lipid A (endotoxin)
- hydrophobic fatty acid chains anchor LPS into the bacterial membrane
- rest of LPS projects from cell surface
- lipid A responsible for much of toxicity of gram -
- upon bacterial lysis by immune system, fragments of lipid A released into circulation = fever, diarrhea, sometimes fatal endotoxic shock septic shock)
Sepsis
organ damage in response to an infection
PAMPs
- peptidoglycan
- LPS
- teichoic acid (gram + cell wall
- capsules
- PRRs allow recognition of molecules broadly shared by pathogens
PRRs - the TLRs
- approx. 10 genes in humans
- TLRs are expressed in all cells of innate immune system (macrophages and dendritic cells in particular)
- recognize diverse molecules on bacteria
- single pass transmembrane proteins/receptors
TLR6
recognizes peptidoglycan in gram +; also lipoteichoic acids in gram +
AND surface proteins (lipoproteins) found on both gram + and gram -
TLR4
recognizes LPS of gram -
LPS can be free floating or associated
TIR
TLR-inducing receptors
= set of proteins that amplify the signal from TLR4 that in turn, the downstream effect is the activation of NF-kappa B (NF-KB) = transcription factor that turns on inflammatory gene expression
NODs
- nucleotide-binding domain, leucine-rich repeat containing receptors)
- sensors of intracellular PAMPs
- overlap between TLR and NOD cascades
- H. pylori
This bacteria often colonizes marine organisms such as copepods, which are important for their transmission
Vibrio cholera
Listeria monocytogenes bacterial structure modifications
Has unusual modifications
- Approx. 50% of NAGs are replaced by just glucosamines
- Virulence factor = PgdA (enzyme that converts NAG to glucosamine) ; allows evasion of NOD-1 (already has modification that evades NOD-2 detection but now sensitive to NOD-1
PgdA
enzyme that converts NAG to glucosamine
- a deacetylase
Listeria expresses surface proteins specialized in the introduction of fine modifications in cell envelope components (to evade recognition)
- Modification of NAG by PgdA
- Glycosylation of teichoic acid (mechanism by which this increases virulence is unknown)
- Listeria is normally positively charged on surface = allows avoidance of AMP binding
Cheap and easy way for bacteria to change it up and avoid detection - just by swapping sugars around
Glycosylation
Antimicrobial peptides
produced by host; non-specifically binds to general neg charge of most bacteria (due to sugars on LPS and teichoic acid)
WTA
wall teichoic acid
- typical teichoic acid is glycosylated
LTA
lipoteichoic acid - mostly composed of residue D-alanine which reduces the neg charge - evades detection by AMPs
Kalata B2 in plants
- shown to have anti-HIV; insecticidal; anti-tumour and anti-microbial activity
- antimicrobial peptides don’t go into a pill form; body destroys when injected; not very well explored
- don’t work in our level of dosage that we need
Action mechanisms of AMPs
- disrupt bacterial cell membrane
- associate with general negative charge that bacterial cells have (AMPs have + charge; non-specifically bind)
- all disrupt bacterial cell membrane by producing non-specific pores
Different AMPs form pores in different ways
- Barrel-Stave model: AMP insert into membrane perpendicularly; AMPs associate with membrane and then push their way in
- Carpet model: small areas of membranes are coded in AMPs (creates pore in membranes)
- Torrodial pore model: resembles Barrel-Stave model except AMP first associates w phospholipid heads (different targets)
Defensin
- AMP example
- short peptide with a positive net charge and a significant proportion of hydrophobic residues (more than 30%) that allows to adopt amphipathic structures in membrane mimicking environments
Example of resistance to defensins (6):
Ex: Listeria = modify teichoic acid with D-alanine; decreases negative charge of cell wall
- Acylation of lipid A which makes membrane harder to penetrate = Salmonella enterica; found in gram negatives (obviously LPS mediated)
- Gram pos/neg; secrete neg charged proteins; acts as a decoy (instead of deterring apps, you just saturate them
- destroy AMPs w proteases
- pump AMPs out of cells (like antibiotics)
- Add positive-charged proteins to outer membrane; gram neg
Dlt protein
covalent modification of cell wall teichoic acid by alanine
MprF protein
covalent modification of membrane phosphatidylglycerol (phospholipid) with L-lysine
Molecular mimickry
structural, functional, or immunological similarities shared between macromolecules found on pathogens and in host tissues
- plays important role in immune responses to infection and in autoimmune diseases
- infection may induce autoimmune responses which attack and destroy body tissues or organs
- pathogens use molecular mimickry to mimic self-antigens of the host to evade the immune system
Guillain-Barre syndrome
- Can occur after campylobacter infection
- Symptoms: neuromuscular and similar to multiple sclerosis (numbing and tingling, fatigue, weakness in hand)
- About 1/100 000
An essential first step in bacterial pathogenesis or infection
Adherence
Adherence for extracellular bacteria
allows them to resist the mechanical clearing mechanisms the host has
Adherence for intracellular bacteria
prerequisite for uptake (invasion)
Bacterial components that mediate interaction between the bacterium and the host cell surface
Adhesins
- very diverse
- can be fimbrial or afimbrial (bacterial cell wall component binds directly to host)
These bind specifically to complementary host cell surface receptors
adhesins; surface molecules on pathogens
These are usually used as receptors for bacterial adhesins
host surface glycans
The most common molecule in mucosal tissue (vast majority of lining between us and environment)
Glycans; therefore, bacteria have evolved a way to attach to it; they can specifically adhere to some of those sugars
Fragile, hairlike processes off bacteria that are frequently replaced due to fragility and so high potential for change/variation
Pili
Chaperone/usher (CU) pathway
- operons that encode three different proteins (at minimum)
- structural protein
- chaperone
- usher (thing that crosses membrane-membrane spanning component)
This capsular antigen is expressed exclusively by Yersinia pestis
F1 pili
F1 pili
- antiphagocytic blocker to prevent uptake of whole pathogen by macrophages
- similar to type I pilus and assembled by chaperone usher system (CU)
F1 capsule consists of a tangle of thin, linear Caf1 fibers
- lots of variability in Caf1; limits vaccine development
- pilus produced at 37 degrees (human) but not at 21-27 (flea)
Twitching motility
Type IV pili can retract while the pilus tip remains firmly adhered to the target surface
A surface motility powered by the extension and retraction of type IV pili; confers slow cell movement, often with a jerky or ‘twitchy’ appearance
Twitching motility
- common to N. gonorrhoea
These are the only pili that can bind DNA
Type IV; N. meningitidis
Horizontal gene transfer
movement and spread of DNA between cells (closely related cells and spreads virulence and antibiotic resistance)
ComP
- meningococcal type IV pili bind DNA through the minor pilin ComP
- it’s their competence protein
- has + charge AA strip that thus binds to - charged DNA (any type of DNA, but really only uptake through homologous DNA)
- shared b/w species
T or F. ComP is highly conserved throughout Neisseria species
T
Sortase enzyme
- enzyme that adds adhesins to cell wall
- group of prokaryotic enzymes that promote covalent anchoring of surface proteins to the cell wall envelope to enable each microbe to effectively interact with its environment
Sortase enzyme main functions
1) sort proteins on the cell surface by covalently joining them to cell wall (attach pilus to cell wall - those that don’t use CUS)
2) polymerize the joining (catalyze covalent bond b/w components of the polymers) proteins that construct the pilus (crucial bc facilitates adhesion)
* *KEY VIRULENCE FACTOR!!**
srtF
- type III pilus housekeeping protein
- can’t polymerize, can only transfer/glue polymerized pilus onto cell wall; limited function!
srtA
- type III pilus
- sortase enzyme
- assembler
- cleaves secreted peptides and covalently links spaA into a pilus
Yersinia lifecycle
1) Pro-phagocytic stage to enter into macrophages and transfer to lymph nodes; live in endosomes; kickstarted by 37 degrees temp
2) Lymph node = it bursts out and an anti-phagocytic stage takes over; we don’t know how it switches or why! or even how it doesn’t get phagocytosed in fleas; but anti-phagocytic stage allows dissemination of infection (once in lymph nodes - inhibits inflammation)
Three bacterial species within the genus Yersinia are causative agents of human disease
- Y. pestis = black plague
- Y. enterocolitica and Y. pseudotubeculosis = enteric pathogens most commonly associated with self-limiting infections of the mesenteric lymph nodes
Non-pili adhesion molecules in Yersinia
YadA and invasin
YadA
- secreted by injectisome
- collagen-binding outer membrane protein
- promotes cell adhesion to eukaryotic host and virulence
- Y. pestis, -pseudotuberculosis, & -enterocolitica encode yadA
- YadA protects bacteria by preventing phagocytosis and it is expressed in a temp. dependent manner
Adhesive protein encoded by the inv gene on the bacterial chromosome
Invasin
This heterodimerizes to mediate adhesion between cell via the extracellular matrix and pathogens
Invasin
- zippers up pseudopodia on the host cell facilitating phagocytosis
- mediates internalization
- probably involved only in early stage of infection although there are some questions of that as well!
Entry of L. monocytogenes into mammalian cells
- requires actin polymerization and membrane remodelling
- example of how a bacterium can manipulate host-cell signalling and endocytic pathways to its advantage
Cadherins
essential components of cell-cell attachment ; part of junctions ; host cell can’t get rid of its cadherins and listeria has figured out a way to sneak its way in between and attach to cadherins
alpha and beta catenin
adaptors part of cadherins and also major signalling molecule ; link cadherins to a particular mammalian actin cytoskeleton
Mice are immune to this pathogen
L. monocytogenes
This is sufficient to confer host specificity on the bacterial pathogen, L. monocytogenes
a single AA at position 16 in E-cadherin
Host range is determined by …
differences in adherence targets amongst species (and amongst individuals)
Iron
- limiting in the body
- crucial for transporting O2
- pathogens can starve us of iron to feed their own metabolismm
Only __% of iron is absorbed
10; most of it is inaccessible
Hepcidin
inhibits iron transport by inhibiting export (regulatory molecule - goes though blood; interacts w spleen, released by liver; signal to other organs the deal with iron - enough or not)
Primary metabolic site of of iron
liver; eating liver is an excellent source of iron
RBC recycling and iron homeostasis
Spleen
Bone marrow
RBC synthesis so iron is trafficked here
Why is Fe a really good oxidizing and reducing agent?
quickly and reversibly interacts with electrons
**redox potential of iron makes it very versatile so that’s why we use it in so many rxns which is good but also bad bc it’s very reactive so having free floating iron (none in the body pretty much), can react w so many things including :
Lactoferrin
- responsible for carrying or ushering Fe3+ to cells
- there are lactoferrin receptors that exist on surfaces to allow for the movement of iron into and around the body
As RBCs get recycled, these bind to lysed hemoglobin
- haemopexin (HPX)
- makes it a danger to be picked up from bacteria OR just protects iron from being free floating
- secondary line of defense
NGAL
- neutrophil gelatinase associated lipocalin
- produced by neutrophils
- chelate siderophores
- inhibits bacterial access to some of the free floating iron or some of the complexed irons present in the body
NRAMP1
- one of the pumps that macrophages use to pump any iron that it may have scavenged (pump it out of lysosome and some endosomes)
Host strategies to prevent pathogens from acquiring iron: (2)
- hide/sequester by binding Fe to heme – then bind to HPX and other heme binding proteins such as ferritin, transferrin, etc.
- to repress iron proteins in response to infection (if u get sick with a bacterial pathogen, you get more pale (looking sick…) due to body stripping itself of available iron to prevent a pathogen from taking hold)
* * ex: hepcidin decreases blood iron = makes u slightly anemic ; hepcidin is released in response to pro-inflam cytokines
Majority of eukaryotic iron is intracellular (2)
- sequestered as ferritin (insoluble)
2. or complexed as predominant iron in our body as heme
Extracellular Fe is insoluble: (2)
- due to neutral pH of serum so therefore iron is difficult to access
- bound to iron associated proteins like transferrin
Microorganisms can overcome iron nutritional limitation in the host by procuring iron:
- extracellularly: from transferrin, lactoferrin, and precipitated ferric hydroxides
- intracellularly: from hemoglobin
T or F. Bacteria can have receptors for iron carrying proteins
T! for hemopexin, transferrin, lactoferrin, hemoglobin, etc.
Siderophores
- iron chelators w/ very high affinity for any iron that might be present (in particular Fe3+)
- chemically diverse; every bacteria will have different way to do this
- all that matters = free oxygens that have free e- that can bind Fe3+ in a suitable angle
Receptor-mediated iron acquisition from host proteins
- uptake in particular of heme (predominant form of iron containing proteins) or other iron containing proteins
How do siderophores work?
bacteria will secrete siderophores, bind to any Fe found and siderophores receptors on surface of cell so they can bring back whatever these iron hunting chemicals have been released and come back home to roost and deliver Fe to bacterial cell
Siderocalin
mammalian lipocalin-type protein that we have developed as a response to bacterial siderophores
These bind to siderophores of bacteria to prevent pathogen from accessing that iron
Siderocalin; siderophore cant go back to deliver back to bacterial cell
UPEC infection cycle:
- Type I fimbriae binds mannose on glycosylate urinary tract epithelial cells (bladder, etc.)
- Rho-GTPase mediates signalling that causes actin reorganization = promotes phagocytosis
- A) Replication in phagosome and exocytosis = slow replication; not a real burst of an infection
B) Vesicle destruction by bacteria allows intracell replication (fast); secrete alpha hemolysin (toxin) produced by E. coli plus others to lyse host cells and liberate Fe C) Enter a more dormant phase; some vesicles do not exocytose nor do they lyse but get encased in actin (host response but pathogen doesn’t mind) = QIRs (quiescent intracell reservoirs) ; can remain viable for months and can cause flare ups of UTIs ; flares under host stress
3B leads to 4 -> release of pathogens once pathogens gains access to host nutrients
Cranberries for UTI?
- Chemical in cranberries binds UPEC (gets in the way) and blocks binding to epithelial cells
- JAMA (2016) = 2016 high dose of cranberry supplements to nursing homes bc as u age, u are not peeing frequently or too much and so UTIs can take hold - also suppressed immune system
- Reduced UTI incidents BUT has not been replicated in the low doses of cranberry juice = doesn’t work …
Tums for UTI?
- Decrease acidity
- UPEC likes high acid of urine so if decrease acidity of urine = may decrease infection by eating base = tums …
- Best solution tho… = pee after sex
Diphtheria toxin
inhibits protein synthesis, leading to epithelial cell damage and myocarditis
Cholera toxin
activates adenylate cyclase, elevates sAMP in cells, leading to changes in intestinal epithelial cells that cause loss of water and electrolytes
Endotoxin
- bacterial LPS toxic to animals
- when injected in small amounts , LPS (endotoxin) activates several host responses that lead to fever, inflammation, and shock
T or F. LPS is an example of an exotoxin
F! endotoxin
Exotoxins
- more specific (whole job is to cause damage)
- secreted toxins
- very high potency
- 3 main types: AB, pore-forming, and superantigens (SAGs)
- *often have specific cytotoxic activity; cell-specific (specifically targets neurons, release of this neurotransmitter, etc.) **
Many bacterial toxins resemble enzymes in several ways :(3)
- proteinaceous
- denaturable (function as folded structures that have specific and unique 3D conformation)
- catalytic activity; can trigger change in function of host cell proteins and also have high degree of specificity of target with specific effect that causes cell damage
Pre-lysosomal compartments
endosomes
ADP-ribosylation
the addition of one or more ADP-ribose moieties to a protein
- required for initiation of disease for several bacterial toxins
Enzymatic function of the A subunit
ADP-ribosylation
Substrate for A enzyme in ADP-ribosylation
NAD (common coenzyme and ADP ribose
T or F. AB toxins have diverse targets of enzymatic activity
T!
Pertussis toxin mode of action
inhibition of cAMP signalling (cAMP increase)
- ADP ribosylates the alpha subunit of a G protein (normally, under uninfected conditions, G protein is a Gi ; but under pathogen conditions = G protein activity is inhibited - so pathway is on… therefore downstream signalling is Upregulated)
cAMP function
- Involved in cytokine release
- insulin release
Result of pertussis toxin interfering with cAMP function
- suppression of cytokine release so reduces innate immune response
- increase insulin release (hormone that cause sugars in bloodstream to be taken up by cell ; causes hypoglycemia - blood sugar drops - tired and sick)
Cholera toxin is secreted by …
type II secretion system
Type II Secretion system of CT
- secretes neuraminidase enzyme (NA) = responsible from removing sialic acid off the host GM1 receptor which allows CT-beta subunit to bind to the receptor
Where does cholera usually colonize?
enterocytes (small intestine)
V. cholera toxin entry
- colonizes small intestine (enterocytes)
- CT is produced and secreted (T2SS)
- CT binds GM1 receptor via B subunit
- Toxin RME into endosome
- Normally after RME, any cargo goes membrane -> endosome -> lysosome
- Alternate pathway for super special things: CT goes membrane -> endocytosed -> endosome -> Golgi and eventually ER (backwards sort of???
○ AT ER : PDI (protein disulfide isomerase) isomerizes/break/unfolds A subunit (held by disulfide bridges) and allows export out of the ER and into cytoplasm (where ADP ribosylate activity) then A subunit refolds where it has ADP-ribosylate activity
CT mode of action
- ADP-ribosylation of G protein and constitutive activation of AC
- results in increased cAMP levels within host cell
- PKA phosphorylates major chloride channels (now doing it all the time rather than being regulated normally ) causes a massive efflux of Cl - from intestinal crypt cells
- > Water follows solute
Pore forming toxins
- protein exotoxins
- typically produced by C. septicum and S. aureus
- frequently cytotoxic; create up-regulated pores in the membrane of targeted cells
- insert a transmembranous pore into a host cell membrane
- disrupt permeability of host -> gains access to host nutrients ; also kills host (LYSIS)
- produced and secreted by pathogens that contain them like alpha toxin from S. aureus (VERY virulent strains) as inactive subunits and self-assemble (at ECF) after activation to form pore at host cell
Molecular mechanism of pore formation
- secreted soluble subunits - bind host at specific receptors (hijacked)
- activation of PFT require association w targets on the host
- form a multimeric pore
- RESULT: efflux of nutrients, (loss of regulation of) ions, anything w osmotic potential… now available to pathogen => host cell damage
2 models of PFT formation:
- Pore forms prior to insertion into host cell membrane (common of the beta toxins)
- Pore assembles during and/or after insertion into host cell membrane (common of the alpha toxins like alpha hemolysin of E. coli and alpha toxin of S. aureus)
Superantigens
- cause non-specific activation of T cells resulting in polyclonal T cell activation and massive cytokine release
- SAGs are produced by some pathogenic viruses and bacteria as a defense mechanism against the immune system
Secreted pyrogenic exotoxins
SAGs
ex: Staph. enterotoxins (A-E, G&H), group A strep A-C, Staph. exfoliatin toxin, Staph. TSST-1
Function of secretion systems
- protection
- transport cell wall, periplasm components
- membrane proteins
- communication
- adhesion
Sec system
Sec system translocates unfolded proteins
- recognizes a hydrophobic N-terminal sequence = leader sequence on translating proteins
- Sec system present in CM of all bacteria
- ATP
Tat system
transports folded proteins
- present in many bacteria
- involves especially proteins that associate with cofactors (easier)
- ATP
Twin arginine translocase
- Tat system
- signal for export is arginines (S-R-R)
This complex forms protein secreting machinery for Tat system
TAT ABC complex
Since T1SS is SEC-independent, how does it transport unfolded proteins?
ABC transporters
Secretion system that secretes alpha hemolysin of UPEC and the lysin/toxin allows further colonization of urinary tract
T1SS; protein folds in ECF of eukaryotes
MARTX
- secreted by V. cholera through T1SS
- facilitates colonization of small intestine
- destroys actin cytoskeleton of host to allow loss of tissue integrity (epithelial layer integrity ) increase colonization of bacteria
Secretion system that’s found in most gram -
- SEC-dependent system
- wide range of substrates
T2SS
- most not involved in pathogenesis ; but broad specificity
T2SS is required for virulence in the following human pathogens:
V. cholerae, L. pneumophila, and enterotoxigenic E. coli
Virulence determinants secreted via T2SS
- ADP-ribosylating toxins of enterotoxigenic E. coli (heat labile)
- CT
- P. aeruginosa exotoxin A
Most toxic virulence factor of pseudomonas
exotoxin A
- a ribosyl transferase that inhibits EF2 in host cells = prevents host cell translation of proteins
Injectisome/T3SS mechanism
- basal rings span bacterial IM and OM
- connects to hollow needle (Yersinia) OR filament (Salmonella)
- tipped with a translocation pore that’s inserted in plasma of target cell
- ATPase at base of injectisome to energize transport
- 2 chaperones aid in assembly of injectisome, while 3rd class assists in translocation of effector proteins
These effectors are eukaryotic-like bacterial proteins
T3S effectors
- interferes with wide range of cell processes
- structure and function resemble proteins found in higher organisms
Injectisomes inject these
- Yersinia YOPS
- Pseudomonas ExoT and ExoS
The most widespread secretion pathway for the transport of molecules across the OM
T5SS
- Yersinia YadA (adhesins)
- VacA of H. pylori (toxins)
Ex: UpaG of UPEC (adhered to ECM of epithelial cells -> invasion ; also allows biofilm formation bc it promotes cell aggregation
T5SS
T6SS
- delivering effector proteins to other cells (gram -)
- phage-tail-spike-like injectisome
- V. cholerae, and P. aeruginosa (bacterial welfare)
ESX-1
- first T7SS discovered in 2003
- involved in lysis of phagosomal membrane and phagosomal escape of mycobacteria
Precancerous lesions of TB
granuloma
TB evading the immune system during latent stage
- they inhibit phagosome maturation as well as translocating from phagolysosome to the cytosol of alveolar macrophage
- down-regulates proinflammatory cytokines, IFN-gamma, and gamma interferon receptor (crucial to T/B-cell responseS)
ESX-5
required for mycobacterial cell wall stability and host cell lysis
This prevents transpeptidation step in cell wall synthesis
Penicillin
Vancomycin
prevents cell wall cross linking; slight difference from penicillin
bacterial specific enzyme in DNA replication that prevents supercoiling during bacterial DNA replication
DNA gyrase = Ciprofloxacin
Tetracycline
blocks bacterial tRNA entrance to the small ribosome
Transformation
- uptake of free DNA from environment
- recipient cells must be naturally competent
- we can induce this in the lab (Cesium chloride in low temps)
- for DNA to be incorporated into recipient cell, must share some sequence HOMOLOGY!!! (doesn’t have to be same genus/species … just some similarity is important!)
Transfer of bacterial DNA using a viral vector; bacterial genome is degraded on viral infections; some chunks of bacterial DNA can be accidentally packaged into a phage head (has viral DNA supposedly.. but instead bacterial DNA accidentally) - next host receives bacterial DNA from phage instead of viral – dead end for the infection but also require sequence similarity!!!
Transduction
Conjugation
- R plasmid = resistance genes = bacteria playing “go fish” trading resistance mechanisms
- direct transfer of DNA between cells
- sharing multidrug resistant plasmid = esp important in hospitals!!!
- Often requires closely related bacteria
Mechanisms of resistance
- impermeable membrane
- multidrug resistance efflux pumps
- resistance mutations
- inactivation of antibiotic
Impermeable membrane
Ex: M. tuberculosis - divide really slowly; mycomembrane is impenetrable to most antibiotics
Ex: some gram negs don’t have porins in OM ; tetracycline NEEDS porins ; not a resistance mechanism?? Just occurs naturally in some bacteria???
Efflux pumps
- Ex: ABC - part of type I secretory systems = how E. coli is resistant to chloramphenicol
- Ex: MFS family… major facilitator family; responsible for tetracycline resistance ; simple H+ antiporter; just a transport proteins (gram +)
- Ex: multidrug and toxic compound extrusion mechanism (MATE) = sodium and proton cotransporter (antiporter); just another transport protein (Only in gram - = RND - resistant nodule family ; pseudomonas aeruginosa = gives broad resistance)
- Ex: small drug resistance; E. coli ; antiporter; small transport proteins that have evolved to recognize antibiotics and pump them out
Resistance mutations
- modify target protein (ex: disabling antibiotic binding site but leaving functionality of protein)
- Ex: gyrase mutations in C. diff make them resistant to a lot of the antibiotics used to target C. diff ; antibiotic resistance leads to diarrhea that never stops
- Ex: small ribosomal unit = streptomycin
Inactivation of the antibiotic
- covalent modification of antibiotic
- catalyzed by acetyltransferases on aminoglycoside
- or by degradation of antibiotic (catalysed by beta-lactamases on beta lactam antibiotics)
T or F. Inactivation by degradation usually occurs outside of bacterium
T!
ESKAPE pathogens
- highly antibiotic resistant bacterial pathogens
- Enterococcus faecium (VRE)
- Staph aureus (MRSA)
- Klebsiella pneumoniae
- P. aeruginosa
VRE
has a mutation = D-alanine- D-lactate (instead of D-alanine - D-alanine residues) SO vancomycin doesn’t recognize!!
Pseudomonas resistance
- widespread resistance to B lactams = penicillin derivatives = prevent cell wall synthesis - BUT now the bacteria have evolved beta lactamases - degrade and inactivate a major class of antibiotics !!! (penicillin and its derivatives)
