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Bacteria Flashcards

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1
Q

Koch’s postulates

A

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

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2
Q

Gram staining

A

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

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3
Q

Exceptions to gram staining

A

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

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4
Q

Cell wall structure

A

Alternating NAM and NAG sugars with horizontal and vertical cross links to connect glycan chains

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5
Q

Protein secretion options

A

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

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6
Q

FtsZ

A

Prokaryotic tubular involved in localising midcill and driving cell separation

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7
Q

Rotary nanomotors

A

Use H+ gradient set up across inner membrane to generate thrust using rotation
Clockwise = random tumbling
Anti-clockwise = swimming straight

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8
Q

Strict anaerobe electron transport chains

A

Used to set up H+ gradient at membrane

Uses CO2 or SO42- as a terminal electron acceptor

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9
Q

Peritrichous flagella

A

All over cell surface e.g salmonella

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10
Q

Operon

A

Group of collinear genes all controlled by a single promoter
Produce polycistronic RNA

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11
Q

Sensing the environment with sensor transducer

A

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
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12
Q

Quorum sensing

A

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

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13
Q

Mechanisms of DNA transferring

A

Conjugation: using F pillus to pull bacteria together for plasmid transfer
Transduction: via bacteriophage injection
Transformation: via uptake of DNA from environment

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14
Q

O antigen

A

LPS

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15
Q

K antigen

A

Capsular polysaccharide

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16
Q

Human vs piglet ETEC adhesion (host tropism)

A

CFA/I in humans

K88 in piglets

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17
Q

Swarming

A

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

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18
Q

UPEC pilli types

A

Type 1 to bind bladder cells at mannose containing receptors

Pap pilli to bind galabiose containing glycolipid receptors in kidney (cause pyelonephritis)

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19
Q

Pedestal formation

A

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

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20
Q

Biofilms

A

3D bacterial population encased in EPS, resistant to host clearance and antiBs
Involves quorum sensing and coordination to build multicellular structure

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21
Q

Biofilm examples

A

Plaque forming strep mutans
Pseudomonas aeruginosa (use alginate polysaccharide for encasing bacteria)
Staphylococcus

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22
Q

Zipper mechanism

A

Listeria, UPEC

Bacterial invasins mimic eukaryotic ligands and bind host integrals to trigger internalisation into endosome

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23
Q

Trigger mechanism

A

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

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24
Q

Transferrin

A

Involved in sequestering Fe in the host to limit bacterial growth

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25
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
26
Resisting low pH of stomach
Secretion of urease to break down urea to NH3 to raise pH Or pumping out H+ Shigella, helicobacter
27
Yop effectors
Made by Yersinia to subvert control of actin cytoskeleton remodelling in macrophages
28
How do capsules help shielding
Can be non-immunogenic e.g silica acid | Can lack affinity for complement factor B
29
Pore forming toxins to kill phagocytic cells
Strep progenies: streptolysin Strep pneumonia: pneumolysin E coli and B pertussis: haemolysin Staph aureus: alpha toxin
30
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
31
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
32
Rheumatic fever
Antibodies against the M protein of Strep pyogenes are cross reactive with rheumatic heart valves
33
Glomerulonephritis
Strep pyogenes Accumulation of Ab-Ag complexes that lodge in glomeruli Type 3 hypersensitivity
34
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
35
Phospholipases (type of cytolysin)
Clostridium perfringens alpha toxin
36
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
37
Where is CTX gene from
Bacteriophage | + coregulated with other virulence factors via HAP signal
38
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
39
Streptococcus equi distinctive virulence factor
Iron binding siderophore equibactin
40
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
41
Enzymatic toxins that are adenylyl cyclase
Bordetella pertussis | Bacillas anthracis
42
Shiga toxin
Depurinates 28S rRNA to block translation
43
EHEC toxin
Shiga-like toxin
44
Clostridium difficile toxin
Glucosylating enzyme that modifies GTPases, changes epithelial tight junctions to allow better bacterial attachment
45
Genotoxins
Cleave DNA in nucleus | S type, E coli, Campylobacter
46
UPEC toxin
Deamidasing | Cytotoxic necrotising factors to deamidate small GTPases
47
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
48
Botulinum toxin
Cleaves synaptobrevin | acts at periphery to stop release of ACh at NMJ
49
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
50
TLR4
LPS lipid A
51
TLR2
Peptidoglycan
52
TLR5
Flagellin
53
Pathways activated following LPS detection
MAPK NFkappaB Get lots of IL-1 and TNFalpha
54
Chronic inflammation examples
Chlamydia: pelvic inflammatory disease | Helicobacter pylori: gastric ulcers
55
Granulomas
TB Leprosy Treponema pallidum (syphillis)
56
Lyme disease
LPS induced inflammation and immune complex deposition in joints and meninges
57
VacA toxin
From helicobacter pylori Anion selective channel Makes endoscope sweet and mitochondria release cytC
58
Example of differential sensitivity of target for selective toxicity
Trimethoprim targets DHFR; bacterial version much more sensitive
59
Example of differential reliance on target for selective toxicity
Sulfonamide targets DHPS; humans get folate from diet so don't need it
60
Enzyme mediated resistance to drugs
Beta lactamases that cleave beta-lactams | Acetyltransferases that modify chloramphenicol and aminoglycosides to stop them binding ribosomes
61
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
62
MDR
Effluc pump used to remove toxic products

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