Bacteria Flashcards
Koch’s postulates
Bacteria present in every case of the disease
Bacteria can be isolated and grown in pure culture
Disease can be reproduced from pure culture in susceptible host
Same bacteria can be isolated from infected susceptible host
Gram staining
Add iodine-crystal violet complex
Was out with ethanol; removes stain in gram -ve
Counter-strain with safranin pink to make gram -ve go red/pink
Exceptions to gram staining
Mycobacterium TB have thick waxy coat to stop crystal violet stain entering but are gram +ve
- Use acid fast
Chlamydia and mycoplasma have unsubstantial cell wall so can’t gram stain
Cell wall structure
Alternating NAM and NAG sugars with horizontal and vertical cross links to connect glycan chains
Protein secretion options
Sec pathway: protein crosses membrane, signal peptidase cleaves the N-terminal export signal
Pilli then use USHER pathway
Or 1 step process with no periplasmic intermediate
FtsZ
Prokaryotic tubular involved in localising midcill and driving cell separation
Rotary nanomotors
Use H+ gradient set up across inner membrane to generate thrust using rotation
Clockwise = random tumbling
Anti-clockwise = swimming straight
Strict anaerobe electron transport chains
Used to set up H+ gradient at membrane
Uses CO2 or SO42- as a terminal electron acceptor
Peritrichous flagella
All over cell surface e.g salmonella
Operon
Group of collinear genes all controlled by a single promoter
Produce polycistronic RNA
Sensing the environment with sensor transducer
AA, pH etc detected by transducer which has kinase activity
- Autokinase activation to phosphorylate His
- This can then transfer the phosphate to Asp on a response regulator
- Response regulator can then act as a TF to alter operon expression
Quorum sensing
Bacteria secrete small signal molecules that other bacteria can measure the conc of and use to modify gene expression
e.g switching on virulence genes for swarming or biofilms when the population is high
Mechanisms of DNA transferring
Conjugation: using F pillus to pull bacteria together for plasmid transfer
Transduction: via bacteriophage injection
Transformation: via uptake of DNA from environment
O antigen
LPS
K antigen
Capsular polysaccharide
Human vs piglet ETEC adhesion (host tropism)
CFA/I in humans
K88 in piglets
Swarming
Coordinated population behaviour for rapid colonisation of epithelial surfaces
Cells sense surface, differentiate into highly motile cells and move
Then stop to divide so population increases before outer layer swarms again
UPEC pilli types
Type 1 to bind bladder cells at mannose containing receptors
Pap pilli to bind galabiose containing glycolipid receptors in kidney (cause pyelonephritis)
Pedestal formation
EPEC and EHEC
Injectosome injects Tir into host cell
Tir is phosphorylated and displayed on host epithelium
Intimin on EPEC/EHEC can then bind Tir; recruiting proteins to cause actin polymerisation below site of adhesion
Biofilms
3D bacterial population encased in EPS, resistant to host clearance and antiBs
Involves quorum sensing and coordination to build multicellular structure
Biofilm examples
Plaque forming strep mutans
Pseudomonas aeruginosa (use alginate polysaccharide for encasing bacteria)
Staphylococcus
Zipper mechanism
Listeria, UPEC
Bacterial invasins mimic eukaryotic ligands and bind host integrals to trigger internalisation into endosome
Trigger mechanism
Salmonella
Injectosome injects Sips into host cell which interacts with host receptors to induce actin polymerisation
Get large scale cytoskeletal rearrangement to give membrane ruffles and bacterial internalisation
Transferrin
Involved in sequestering Fe in the host to limit bacterial growth
Evading lack of iron in host
Bacteria can secret sidophores with high affinity for Fe and then reimport them
e.g Pseudomoas Aeruginosa making pyoverdin
Resisting low pH of stomach
Secretion of urease to break down urea to NH3 to raise pH
Or pumping out H+
Shigella, helicobacter
Yop effectors
Made by Yersinia to subvert control of actin cytoskeleton remodelling in macrophages
How do capsules help shielding
Can be non-immunogenic e.g silica acid
Can lack affinity for complement factor B
Pore forming toxins to kill phagocytic cells
Strep progenies: streptolysin
Strep pneumonia: pneumolysin
E coli and B pertussis: haemolysin
Staph aureus: alpha toxin
Salmonella flagellin expression control
Has two genes to encode flagellin
First gene has promoter that also drives transcription of a repressor of the second gene
At low freq the promoter of the first gene recombines via L and R recombination sites
Therefore no more transcription of gene 1 or repression of 2
Neisseria pilin genes
Have many pili encoded at different silent loci
Recombination allows expression of new pilin gene if it enters expression loci
These genes are sourced from the environment via transformation
Rheumatic fever
Antibodies against the M protein of Strep pyogenes are cross reactive with rheumatic heart valves
Glomerulonephritis
Strep pyogenes
Accumulation of Ab-Ag complexes that lodge in glomeruli
Type 3 hypersensitivity
Bacteria that survive in macrophages
Salmonela typhi
Mycobacteria
Legionella pneumophilia in alveolar macrophages
Inhibit phagosome-lysosome fusion with proteins and resist oxidative burst with enzymes/waxy envelope
Phospholipases (type of cytolysin)
Clostridium perfringens alpha toxin
Cholera toxin
ADP-ribosylating enzyme
Pentamer of B subunits with central A subunit
B subunit binds gangliocyte receptor GM1-ganglioside
Get endocytosis
Retrograde transport of CTX to Golgi then ER
A subunit dissociates and ADP-ribosylates Gs to fix it ON
So cAMP rises which opens CFTR channels to get Cl- loss and diarrhoea
Where is CTX gene from
Bacteriophage
+ coregulated with other virulence factors via HAP signal
Diptheria toxin
From Corynebacteria; C diphtheria (humans), C ulcers and C pseudo tuberculosis in animals
- Form a pseudomembrane from dead host cells
Gene is from corynephage
B domain binds heparin binding epidermal growth factor receptor on host cell surface and is endocytosed
Host cell furins cleave toxin during this
A fragment acts on EF2 protein at ribosome to stop translation
Streptococcus equi distinctive virulence factor
Iron binding siderophore equibactin
How does diphtheria toxin expression
Regulated by repressor DtxR which binds to promoter when bound by Fe so no transcription
When Fe is low in host, can’t repress transcription so toxin is made
Enzymatic toxins that are adenylyl cyclase
Bordetella pertussis
Bacillas anthracis
Shiga toxin
Depurinates 28S rRNA to block translation
EHEC toxin
Shiga-like toxin
Clostridium difficile toxin
Glucosylating enzyme that modifies GTPases, changes epithelial tight junctions to allow better bacterial attachment
Genotoxins
Cleave DNA in nucleus
S type, E coli, Campylobacter
UPEC toxin
Deamidasing
Cytotoxic necrotising factors to deamidate small GTPases
Tetanus toxin
B chain causes endocytosis
Retrograde transport to CNS
TeNT is protease that cleaves SNARE synaptobrevin to block release of glycine/GABA
Spastic paralysis
Botulinum toxin
Cleaves synaptobrevin
acts at periphery to stop release of ACh at NMJ
Superantigen toxins
Binds and bridges weakly interacting MHC and TCR
This activates useless T cells to cause cytokine storm that damages host
Staphylococcal toxins, TSS, strep progenies
TLR4
LPS lipid A
TLR2
Peptidoglycan
TLR5
Flagellin
Pathways activated following LPS detection
MAPK
NFkappaB
Get lots of IL-1 and TNFalpha
Chronic inflammation examples
Chlamydia: pelvic inflammatory disease
Helicobacter pylori: gastric ulcers
Granulomas
TB
Leprosy
Treponema pallidum (syphillis)
Lyme disease
LPS induced inflammation and immune complex deposition in joints and meninges
VacA toxin
From helicobacter pylori
Anion selective channel
Makes endoscope sweet and mitochondria release cytC
Example of differential sensitivity of target for selective toxicity
Trimethoprim targets DHFR; bacterial version much more sensitive
Example of differential reliance on target for selective toxicity
Sulfonamide targets DHPS; humans get folate from diet so don’t need it
Enzyme mediated resistance to drugs
Beta lactamases that cleave beta-lactams
Acetyltransferases that modify chloramphenicol and aminoglycosides to stop them binding ribosomes
Altering target in drug resistance
Making ribosomal protection proteins to dislodge tetracycline
Qnr protein to bind topoisomerase and prevent fluoroquinolone access
Replacing D-ala-Dala with D-Ala-D-lac to stop vancomycin binding it
MDR
Effluc pump used to remove toxic products
