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Medical Microbiology > Lecture 5 > Flashcards

Lecture 5 Flashcards

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Biology 101 flashcards USMLE® Step 1 flashcards
1
Q

What are biofilms?

A
  • Conditioning firm of organic and inorganic particles
  • Bacteria arrive on surface
  • Bacteria attach (reversible/irreversible)
  • Biosynthesis of matrix
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2
Q

3 ways bacteria bind to surface

A

Diffusion
Motility chemotaxis
Turbulence impaction

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3
Q

Arrival of bacteria to surface layers

A
  • Flow of fluid or air
  • Boundary layer (no flow)

Surface

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4
Q

laminar flow

A

Bacteria on separate layers

The boundary layer is not affected (no flow)

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5
Q

Turbulent flow

A

Lots of mixing between bacteria

Boundary layer disturbed

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6
Q

How is turbulent flow made greater

A

Rough surfaces

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7
Q

Brownian movement

A

30-100nm from surface as negatively charged surfaces repel

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8
Q

Bridging structures

A

Generic adhesions - flagella, fimbriae, pili, stalks, teichoic acids

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9
Q

Are brownian movement and bridging sturctures reversibly or irreversibly bound?

A

Reversibly bound

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10
Q

Name generic adhesions

A

Pili, fimbriae, flagella, teichoic acids etc

Bind specifically or non-specifically

Specifically - pathogenic bacteria, some non-pathogenic bacteria, mainly glycoprotein receptors

Non-specifically - Electrostatic forces (abiotic surfaces + conditioning film)

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11
Q

What are teichoic and lipoteichoic acids made of?

A

Fibronectin - Glycoprotein (mannose)

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12
Q

What do flagella bind to?

A

Toll-like receptor 5

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13
Q

What specific sugars are found in glycoprotein receptors

A

Mannose - Vibrio chloerae, Escherichia coli

Galactose - Neisseria gonorrhoeae, Bordetella pertussis

Fucose - Vibrio cholerae

Glucosamine - Neisseria gonorrhoeae

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14
Q

What are attachment proteins?

A
  • Sugar-binding proteins
  • Encoded in plasmids
  • Sugar residues in host receptors - glycans, glycoproteins, and glycolipids
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15
Q

What are the attachment proteins for Yersinia, Salmonella, and Neisseria?

A

YadA

SadA

NadA

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16
Q

Attachment proteins for E. coli and Haemophilus influenze?

A

Hia and Hsf proteins

EibA-G protein

17
Q

Gram positive attachment proteins

A

Group A Streptococci - Protein M

S. aureus - protein A

C. difficile - CbpA

18
Q

Name examples of irreversibly bound bacteria to surface mechanisms

A

Phenotypic switch

Exopolymer deposition

Cemented

19
Q

Reversible to irreversible attachment

A
  • Attachment and adhesions form clusters
  • Cell communication after enough cells have clustered
  • alg - Important gene
  • Over-secrete alginate to form slime
  • Cements cells to surface
  • Mature Biofilm forms via in-house division
20
Q

Cell-cell signalling

A

Synthesis -> Recognition -> Response

Gram +ve - Oilgopeptides used
Gram -ve - AHLs or HSLs used

21
Q

N-Acyl-Homoserine Lactones types

A

OHHL (OC6) - Erwinia and Yersinia

BHL (C4) - P. aeruginosa

OdDHL (OC12) - P. aeruginosa

22
Q

Cell signalling in same species cells

A

Low HSL conc
Below threshold conc
No co-ordinated response

High HSL conc
Above threshold conc
Co-ordinated response

23
Q

Other name for threshold density

A

Quorum

24
Q

What does Allvibrio and Photobacterium fisheri show?

A

Bioluminescence

25
Q

What do LuxR and LuxI encode?

A

Regulatory genes

LuxR - Activator proteins
LuxI - HSLs

Promoters for both operons

26
Q

What does Lux A-E encode for?

A

Structural genes

Light production

27
Q

What do LuxI operons cause

A
  • When sessile, 50-60 changes in gene expression
  • Down-regulation of planktonic genes
  • Up-regulation or new expression of beneficial genes e.g. extracellular polysaccharides, antibiotic production, virulence factors
28
Q

What are some species with LuxI/LuxR homologues?

A
  1. Vibrio cholera
  2. E. coli H2
  3. P. aeruginosa
29
Q

What is a mature biofilm matrix made from?

A

~98% water
~2-5% cells

30
Q

Exopolymeric substances

A

Absorbed materials - Nutrients, waste

Biosynthetic microbial polymers - Extracellular polysaccharides, nucleic acid, proteins, glycoproteins, phospholipids

31
Q

What do exopolymeric substances do?

A
  • Cellular cement
  • Form matrix framework
  • Provide structure
  • Defined architecture to biofilms
32
Q

Where is there higher bacterial growth and EPS production in biofilms?

A

Layers closer to nutrients

33
Q

Biofilm topography

A
  • Low flow rate
  • Slow growth, compact
  • Most biofilms
  • High flow rate
  • Rapid growth, prone to sloughing
  • Unstable
34
Q

Sloughing

A

Turbulence, scouring and direct or indirect grazing of biofilm

35
Q

Programmed detachment

A
  • Synchronised liberation of daughter cells
  • More hydrophilic
  • Down regulation of high mwt LPS
  • Leaves low mwt LPS
  • Shot out of the biofilm
  • 2-3 division before attachment
36
Q

What are cells embedded in biofilm matrix protected from?

A
  • Desiccation
  • Starvation
  • Poisoning
  • Predation
  • Colonisation
37
Q

Are bacteria close in biofilms

A

Yes, with pooled extracellular enzymes and greater resistance to antimicrobial compounds

38
Q

Why are biofilms more difficult to kill?

A
  • Stress tolerance
  • Less diffusion in matrix
  • Can require 1000x high conc of antimicrobial agent
39
Q
A

Medical Microbiology (18 decks)

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