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BOD > Bacteria > Flashcards

Bacteria Flashcards

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
Q

Evading lack of iron in host

A

Bacteria can secret sidophores with high affinity for Fe and then reimport them
e.g Pseudomoas Aeruginosa making pyoverdin

26
Q

Resisting low pH of stomach

A

Secretion of urease to break down urea to NH3 to raise pH
Or pumping out H+
Shigella, helicobacter

27
Q

Yop effectors

A

Made by Yersinia to subvert control of actin cytoskeleton remodelling in macrophages

28
Q

How do capsules help shielding

A

Can be non-immunogenic e.g silica acid

Can lack affinity for complement factor B

29
Q

Pore forming toxins to kill phagocytic cells

A

Strep progenies: streptolysin
Strep pneumonia: pneumolysin
E coli and B pertussis: haemolysin
Staph aureus: alpha toxin

30
Q

Salmonella flagellin expression control

A

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
Q

Neisseria pilin genes

A

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
Q

Rheumatic fever

A

Antibodies against the M protein of Strep pyogenes are cross reactive with rheumatic heart valves

33
Q

Glomerulonephritis

A

Strep pyogenes
Accumulation of Ab-Ag complexes that lodge in glomeruli
Type 3 hypersensitivity

34
Q

Bacteria that survive in macrophages

A

Salmonela typhi
Mycobacteria
Legionella pneumophilia in alveolar macrophages

Inhibit phagosome-lysosome fusion with proteins and resist oxidative burst with enzymes/waxy envelope

35
Q

Phospholipases (type of cytolysin)

A

Clostridium perfringens alpha toxin

36
Q

Cholera toxin

A

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
Q

Where is CTX gene from

A

Bacteriophage

+ coregulated with other virulence factors via HAP signal

38
Q

Diptheria toxin

A

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
Q

Streptococcus equi distinctive virulence factor

A

Iron binding siderophore equibactin

40
Q

How does diphtheria toxin expression

A

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
Q

Enzymatic toxins that are adenylyl cyclase

A

Bordetella pertussis

Bacillas anthracis

42
Q

Shiga toxin

A

Depurinates 28S rRNA to block translation

43
Q

EHEC toxin

A

Shiga-like toxin

44
Q

Clostridium difficile toxin

A

Glucosylating enzyme that modifies GTPases, changes epithelial tight junctions to allow better bacterial attachment

45
Q

Genotoxins

A

Cleave DNA in nucleus

S type, E coli, Campylobacter

46
Q

UPEC toxin

A

Deamidasing

Cytotoxic necrotising factors to deamidate small GTPases

47
Q

Tetanus toxin

A

B chain causes endocytosis
Retrograde transport to CNS
TeNT is protease that cleaves SNARE synaptobrevin to block release of glycine/GABA
Spastic paralysis

48
Q

Botulinum toxin

A

Cleaves synaptobrevin

acts at periphery to stop release of ACh at NMJ

49
Q

Superantigen toxins

A

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
Q

TLR4

A

LPS lipid A

51
Q

TLR2

A

Peptidoglycan

52
Q

TLR5

A

Flagellin

53
Q

Pathways activated following LPS detection

A

MAPK
NFkappaB

Get lots of IL-1 and TNFalpha

54
Q

Chronic inflammation examples

A

Chlamydia: pelvic inflammatory disease

Helicobacter pylori: gastric ulcers

55
Q

Granulomas

A

TB
Leprosy
Treponema pallidum (syphillis)

56
Q

Lyme disease

A

LPS induced inflammation and immune complex deposition in joints and meninges

57
Q

VacA toxin

A

From helicobacter pylori
Anion selective channel
Makes endoscope sweet and mitochondria release cytC

58
Q

Example of differential sensitivity of target for selective toxicity

A

Trimethoprim targets DHFR; bacterial version much more sensitive

59
Q

Example of differential reliance on target for selective toxicity

A

Sulfonamide targets DHPS; humans get folate from diet so don’t need it

60
Q

Enzyme mediated resistance to drugs

A

Beta lactamases that cleave beta-lactams

Acetyltransferases that modify chloramphenicol and aminoglycosides to stop them binding ribosomes

61
Q

Altering target in drug resistance

A

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
Q

MDR

A

Effluc pump used to remove toxic products

BOD (7 decks)

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