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Cells to Organisms 1 > 5 & 6 -Intro to Bacterial cell envelope > Flashcards

5 & 6 -Intro to Bacterial cell envelope Flashcards

1
Q

What three things must a pathogen do to colonise/infect a host?

A

1) Gain access to hose
2) Adhere to host surfaces
3) Evade Host defences

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2
Q

What is the difference between the inner and outer membrane of gram-negative bacteria?

A

Inner membrane, both faces made of phospholipid bilayer

Outer membrane, inner face = phospholipids, outer face = LPS (lipopolysaccharide)

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3
Q

Give 3 functions of the outer membrane in gram-negative bacteria

A

Structure - mechanical stability, (needed as gram-negative don’t have thick peptidoglycan wall)

Defense - Protects against antibiotics, bacteriophages, antimicrobial peptides

Permeability Barrier - Stops things permeating cell envelope, like detergents, needed as no thick peptidoglycan wall

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4
Q

What are the 3 key areas that form LPS?

A

Lipid A - embedded in membrane
Core oligosaccharide region
O-antigen region - important for virulent response

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5
Q

What are three functions of LPS?

A

Barrier Function -> repels hydrophobic agents, detergents, bile and antibiotics

Forms tightly packed layer -> due to strong lateral interactions between LPS molecules

Pro-inflammatory -> Interacts with receptors on macrophages, and B-cells leading to cytokine release.

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6
Q

Which part of LPS is also called endotoxin and why?

A

Lipid A, due to role in proinflammation

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7
Q

What short sugars is the core oligosaccharide made of?

A

D-galactose or D-glucose

Occasionally heptose / keto deoxyoctanate

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8
Q

Is O-antigen region highly conserved or highly variable?

A

Highly variable
Composition can change between strains of a pathogen
E.coli has approx 160 different O-antigen structures

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9
Q

What is rough LPS?

A

No O-antigen / O- polysaccharide present

Only core oligosaccharide attached to lipid A present.

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10
Q

What is smooth LPS?

A

All three regions are present ; Lipid A, Core Oligosaccharide, O-Polysaccharide/Antigen.

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11
Q

Why would losing the O-antigen be beneficial to bacteria?

A

O-antigen causes virulence and triggers and immune response.

Losing it allows the bacteria to maintain chronic infection and go undetected by the immune system

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12
Q

Give two examples of bacteria that alter their LPS

A

Vibrio Cholerae

Helicobacter Pylori

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13
Q

What does the addition of a positively charged amino acid to LPS in bacteria such as Vibrio Cholerae do?

A

Removes negative charge on lipid A and increases resistance to cationic antimicrobial peptides.

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14
Q

Give two features found on the surface of gram-positve bacteria.

A

Teichoic acids

Covalently bound anchor proteins

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15
Q

Are Teichoic acids negatively or positively charged?

What molecules give them this charge?

A

Negatively charged

Phosphates in the polymer chain

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16
Q

What are the two types of teichoic acids?

Where are they found?

A

Wall teichoic acids -> embedded in cell wall

Lipoteichoic acids -> embedded in cytoplasmic membrane

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17
Q

What groups can bacteria add to teichoic acids?

A

Glycosyl groups

Positively charged amino acids

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18
Q

What are six functions of teichoic acids?

A

Important in bacterial growth and division

Negative charge protects from antimicrobials and antibiotics

Allow bacteria to bind to surfaces, (mucosal surfaces in host)

Prevent/block host from binding to peptidoglycan

Contribute to virulence

The molecules host cells recognise and trigger an immune response (modifications made to evade this recognition)

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19
Q

Is the polymer chain of teichoic acids very conserved or very variable in a given species?

A

Highly conserved

the modifications are highly variable however

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20
Q

What are the two types of modification teiochoic acids can have?

A

D-alanine

Glycosylation

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21
Q

What effect does the addition of D-alanine have on teiochoic acids?

A

Advantage:
Positively charged amino acid, infers increased resistance to; host defences, antimicrobial peptides and glycopeptide antibiotics (antibiotics that inhibit cell wall synthesis)

Disadvantage:
Can prevent adhesion to host cells and thus prevent establishing and infection

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22
Q

What effect does glycosylation of teiochoic acids have on bacteria?

A

Advantage:
Increases protection from the immune system

Disadvantage:
Increase susceptibility to phages as viruses can recognise the glycosyls on teiochoic acids and use it to infect bacteria

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23
Q

Are modifications permanent?

A

No they fluxuate through time and are not fixed

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24
Q

Are modifications more common in early infection of chronic infection?

A

More common in chronic infection

25
Q

Where are covalently bound proteins attached to on the cell surface?

A

Anchored to amino acid cross-bridges in peptidoglycan of bacteria.

26
Q

What are 6 functions of covalently bound anchored proteins?

A 
Bacterial adhesion
Invasion of host cell
Bind to plasma protein
Immune evasion
Induce inflammation
Biofilm formation
27
Q

What enzyme attaches anchor proteins to cross-bridges?

A

Sortase

28
Q

What is the phenotype of SrtA mutants?

How does this effect the bacteria?

A

No cell wall anchored proteins

Much less virulent -> cell wall anchored proteins increases virulence.

29
Q

Name three structures beyond the cell wall that are important in adhesion and colonisation.

A

Pili
Capsule
Flagella

30
Q

What are EPS?

When is it produced?

A

Extra cellular polysaccharides
Secreted into the environment, NOT retained on the cell surface.

During biofilm formation.

31
Q

What part of bacteria is a type of glycocalyx?

A

The capsule

32
Q

What are the two types of capsules?

What are their differences?

A

‘True Capsule’ - distinct layer and gelatinous

Slime layer - irregular/ diffuse layer (slimy!)

33
Q

What does hyaluronic acid in a capsule do?

A

Retains water

34
Q

In what way are capsules important for virulence?

A

Resist phagocytosis, ‘hide’ surface structures from immune cells

35
Q

Give an example of an encapsulated bacteria

What disease does it cause?

A

Bacillus anthracis

Anthrax (only encapsulated strains cause disease)

36
Q

What are 4 functions of a capsule?

A

Barrier to toxic hyrdrophobic molecules, e.g. detergents. This is due to high water content.

Water content protects against dessication

Prevents bacteriophage infection by hiding surface structures

Hides bacteria from host immune system

37
Q

How does the capsule avoid destruction?

A

Prevents complement-mediated lysis

38
Q

How does the capsule avoid detection?

A

Hide surface structures to resist phagocytosis

39
Q

Give an example of bacteria that resist phagocytosis

A

streptococus pneumoniae

40
Q

What are opsonins?

A

Bind to foreign microorganisms/ pathogens to make them more susceptible to phagocytosis

e.g. antibodies, complement produced by immune system

41
Q

How do opsonins trigger phagocytosis?

A

White blood cells have opsonin receptors,

Bind to osponins on pathogens and then phagocytose the bacterium

42
Q

What effect does the capsule have on opsonins?

A

Prevents white blood cells from detecting/binding to opsonins

43
Q

What are the four stages of forming a biofilm?

A

1) Adhesion to surface
2) Cell- Cell Communication
3) Proliferation
4) Maturation

44
Q

Where is the S-layer located?

A

Between the outer membrane and biofilm

Not the outermost layer, that’s the capsule.

45
Q

What do pores in the S-layer allow for?

A

Selective permeation of different products

46
Q

S-layers are commonly found in archaea. True or False?

A

True, they protect them from harsh environments

47
Q

Are S-layers found in gram-positive or gram-negative bacteria or both?

A

Both and many don’t have one at all

48
Q

Give 3 functions of the S-layer

A

Molecular Sieve (porous mesh like chain mail)

Protection (against bacteriophages, complement (opsonins), phagocytosis, extreme environments)

Adherence (proteins adhere to epithelial mucosal cells)

49
Q

What protein are pili made of?

A

Pilin

50
Q

What are sex pili used for?

A

Transferring genetic material from one bacterium to another.

51
Q

What are ordinary pili used for?

A

Attach to surfaces and other bacteria

Motility - crawling/twitching

52
Q

Are pili mostly found in gram-positive or gram-negative bacteria?

A

Gram-negative

53
Q

What do major and minor pilin proteins do?

A

Major pilin forms the Shaft

Minor pilin forms the tip

54
Q

Describe the role of Type 4 (IV) pili in P. aeruginosa

A

Adherence to surface in host - sense initial contact, triggering a virulence cascade

Biofilm formation (important for evading immune system)

Twitching & Motility

Switch from virulent to non-virulent strains

55
Q

How many pili and how many fimbriae are found on a typical bacterium?

A

1-2 pili

100’s - 1000’s fimbriae

56
Q

Are fimbriae found in gram-positive, gram-negative bacteria or both?

A

Both

57
Q

What is the function of fimbriae?

A

Attachment to surfaces / tissues

Clinging to other bacteria

Adhesion molecule at tip of fimbriae allows attachment to specific host molecules

58
Q

List the 4 main components of a fimbriae structure

A

Tip (adhesion protein)
Fibrillium
Rod
Pore

59
Q

What two virulence factors are found in uropathogenic E. coli (UPEC)?

A

Fim H (Type I fimbriae) - recognise elements of epithelial cell membrane to attach

P fimbriae - recognise receptor proteins on cell membrane & form contact

Cells to Organisms 1 (19 decks)

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