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HHAD: Microbiology > Biofilms and polymicrobial infections > Flashcards

Biofilms and polymicrobial infections Flashcards

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1
Q

What is the definition of a classical infection?

A

Single organism of exogenous source (i.e. not part of normal flora).
Organism colonises susceptible host where it multiplies and evades host defence.
It damages host, normally by production of protein toxin (exotoxin)

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2
Q

What is a polymicrobial infection?

A

Where numerous species/microbes are involved, no single organism associated with disease.
Impossible to apply Koch’s postulates to this scenario

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3
Q

Outline how an initial viral infection in the lungs could lead to a secondary bacterial infection

A
  1. Initial viral infection causes damage to lung tissue
  2. Tissue damage then exposes basement membrane elements (e.g. fibrinogen) to which bacteria can adhere and infiltrate into the host
  3. Viral neuraminidase cleaves sialic acid residues on host cells. This creates more bacterial binding sites.(neuraminidase inhibitors reduce s pneumoniae infiltration in experimental models)
  4. Bronchitis or pneumonia cause by strep pneumoniae, haemophilus influenzae or S. Aureus
  5. Impaired host immune response
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4
Q

How could an over-activity of the immune system lead to infiltration of bacteria, lymphocytes, neutrophils and macrophages?

And what is the consequence of this?

A

Over production of inflammatory cytokines

(in the lung scenario): alveolar architecture is damaged.

Secondary bacterial infection leads to more prolonged and severe clinical symptoms when compared to viral infection alone. This bacterial invasion can lead to septicaemia - can lead to death.

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5
Q

What 3 factors underpin septicaemia?

A

Virus
Bacteria
Host immune response

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6
Q

What is the definition of a biofilm?

A

Biofilms are complex and dynamic structures.
A matrix-enclosed population of microbes that can adhere to biotic and abiotic substrates.

Biofilms are the most prevalent manifestation of polymicrobial communities.

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7
Q

Give 3 examples of biotic substrates

A

Skin
Mucosal surfaces
Teeth

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8
Q

Give 3 examples of abiotic substrates

A 
Dentures/acrylics/resins
IV/urinary catheters
Abdominal drains
Stents
Ventilator tubes
Feeding tubes
Contact lenses
Heart valves
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9
Q

Why does the composition of a biofilm change?

A

It changes in response to changes in the environment

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10
Q

What 2 adjectives would you use to describe biofilm development in the oral cavity

A

Continuous

Sequential

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11
Q

Name 2 examples of early colonisers in the dental biofilm

A

Strep sp.

A. Naeslundii

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12
Q

Name 3 examples of late colonisers in the dental plaque biofilm

A

P. gingivalis
T. Denticola
T. Forsythia

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13
Q

Which bacteria acts as a bridging species in the dental plaque biofilm?

A

F. nucleatum

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14
Q

What does EPS stand for?

A

Extra polymeric substances

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15
Q

What are mature biofilms encased in?

A

A matrix of extrapolymeric substances

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16
Q

Name the 4 substances that are extrapolymeric substances (EPS)

A

Polysaccharides
Proteins
Lipids
Extracellular nucleic acid

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17
Q

What are the 4 advantages of the EPS matrix?

A
  1. Mechanical stability
  2. Facilitates cell to cell interaction
  3. Reduced efficacy of antimicrobials/immune cells
  4. Microbes that grow in a biofilm are less sensitive to antibiotics than those that live free in suspension
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18
Q

Outline the advantages of life in a biofilm over planktonic growth (5)

A
  1. Increased metabolic fitness: nutritional cooperation
  2. Increased genomic diversity: horizontal gene transfer antibiotic resistance
  3. Increased stress resistance (biological/chemical/physical)
  4. Aerobic bacteria can lower oxygen tension providing the means for anaerobic species to survive
  5. Recalcitrance: reduced antibiotic penetrance into the biofilm, reduced antibiotic diffusion within the biofilm
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19
Q

In what 2 states could you find an oral biofilm

A

healthy or dysbiotic

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20
Q

What are the 3 basic steps of biofilm formation?

A
  1. Adhesion
  2. Microcolony
  3. Mature biofilm
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21
Q

What type of microbes are more abundant in a healthy biofilm?

A

gram positive facultatives

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22
Q

What type of microbes become more abundant as a biofilm ages and develops towards disease?

A

Gram negative anaerobes

23
Q

Why is periodontitis a biofilm disease?

A

It is a polymicrobial infection of the subgingival crevice.

It is associated with a shift in gram status of the microbiota and chronic inflammation of the gums.

24
Q

Describe the transition in resident microbiota from healthy to peridontitis

A

Healthy microbiota > [Subtle changes in COMPOSITION of microbiota] GINGIVITIS > [Stabilisation of dysbiotic polymicrobial community] PERIDONTITIS

25
Q

What are the consequences of periodontitis (2)

A

Damage to structures supporting the tooth.

Resorption of alveolar bone - tooth loss.

26
Q

What are 3 examples of biofilm infections other than perio?

A 
Medical plastics (e.g. catheters)
Prosthetic heart valve endocarditis
Contact lens keratitis
27
Q

Alongside high blood sugar, what triggers diabetic foot ulcers (DFU)?

A

Inappropriate foot care

Foot injuries

28
Q

What 3 underlying conditions could be involved in diabetic foot ulcers?

A

Nerve damage (neuropathy)
Reduced blood flow (microangiopathy)
Chronic inflammation

29
Q

What would the microbiota be like in a case of diabetic foot ulcers?

A

Host microbiota is dysbiotic

Biofilms formed

30
Q

How would you describe the polymicrobial interactions within biofilms?

A

Numerous, dynamic and complex

31
Q

Name the 3 polymicrobial interactions found within a biofilm

A
  1. Physical interaction > co-aggregation
  2. Chemical interactions > quorum sensing
  3. Nutritional interaction > Digestive consortiums
32
Q

What is co-aggregation?

A

It is a process whereby genetically distinct bacteria attach to each other via specific molecules called adhesins

33
Q

What are planktonic cells?

A

They are free-swimming cells

34
Q

What can co-aggregates influence in a polymicrobial biofilm?

A

It can influence the development and composition of the biofilm

35
Q

Outline the interaction between Candida albicans (fungi) and S. Aureus (bacteria)

Also give an example of where this interaction may be found in a real-life scenario

A

C Albicans produces hyphae, which are pathogenic invasive filaments.
S. aureus can adhere to this hyphae.
Systemic bacterial infection is facilitated by invasive hyphal filaments.

Scenario: hospitals - catheters, IV, abdominal drains frequently affected

36
Q

Outline denture stomatitis and how it is a biofilm mediated condition

A

Polymicrobial biofilm-mediated condition

Biofilm accumulates on dentures and is colonised by fungi

Constant contact of fungal/bacterial biofilm with the oral mucosa

Poor dental hygiene and failure to remove dentures allow bacteria, fungi and associated virulence factors to cause inflammation

37
Q

What is quorum sensing?

A

It is the regulation of gene expression in response to fluctuations in cell-population density.

38
Q

What do microbes secrete in quorum sensing?

A

Quorum sensing molecules (QSM)

39
Q

When quorum sensing molecules (QSM) are present in sufficient concentrations what happens?

A

They induce the expression or repression of quorum-dependent target genes. i.e. changes in transcriptional activity

40
Q

At what point in quorum signalling does specific changes in population behaviour occur?

A

When a critical threshold of signalling is exceeded

41
Q

Name 3 bacterial quorum sensing molecules

A

Autoinducer-2 (G negative and gram positive bacteria)

N-Acyl Homoserine Lactones (NAHL) (Gram negative bacteria)

Competence signalling peptides (Gram positive bacteria)

42
Q

Name a QSM that inhibits Candida Albicans filamentation

A

Farnesol

43
Q

What is particularly important for biofilm PERSISTENCE?

A

Acquisition of nutrients

44
Q

What are the principal substrates available in the mouth?

A

Proteins
Sugars
Glycoproteins (albumin, mucins, transferrins)

45
Q

If individual microbial species cannot break down substrates on their own, how do they gain nutrients?

A

Via digestive consortiums - species cooperate.
Complex substrates are broken down into various sub sections by different species until they are simple molecules and can be utilised. At each step of the breakdown, a different molecule is made and can be utilised by a different species.

46
Q

What are accessory pathogens?

A

They are commensal microbes that can support or enhance the virulence of a different organism

47
Q

If endogenous oral microbes are introduced into a normal sterile tissue - what happens?

Is it just one type of bacteria that causes this or is it polymicrobial?

A

Abscess

Polymicrobial

48
Q

Name 3 ways microbial communities cooperate to avoid host immune responses

A
  • Subversion of complement (P gingivalis, T forsythia)
  • Manipulation of neutrophils (P gingivalis)
  • Inhibition of macrophage responses (P Gingivalis)
49
Q

Roughly how many different bacterial species can be in a single periodontal pocket?

A

over 100

50
Q

How does some ‘unculturable’ bacteria i.e. bacteria that do not grow by themselves grow?

A

They have ‘helper’ strains

51
Q

What may be problematic if an infection is composed of multiple species?

A

Detection and Identification

52
Q

What are the issues with diagnosing polymicrobial infections?

A

It is time consuming and costly.
Organisms are present in varying numbers - so sometimes difficult to detect lower levels of pathogens.
Can be difficult to identify organisms to species level

53
Q

What technique can be used to identify the genus of microbes in a polymicrobial community?

A

16S rRNA next-generation sequencing and OTU determination

54
Q

Why is it difficult to treat polymicrobial infections?

A
  • Very diverse: they display many complex phenotypes involving multiple virulence factors
  • Difficult to choose an individual antimicrobial; not all organisms may respond
  • Resistance to antimicrobials and antibiotics is growing concern
  • Outcomes are difficult to predict.

HHAD: Microbiology (6 decks)

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