BK - Biofilm Physiology and Quorum Sensing I Flashcards
What is a biofilm? (2)
- Aggregated bacterial cells often attached to a surface
- Embedded in a self-made biopolymeric matrix
Why are biofilms significant in bacterial infections? (3)
- Cause chronic bacterial infections
- Protect bacteria from the immune system
- Increase tolerance to high doses of antibiotics
What are some primary sites of biofilm infections in the body? (3)
- Mouth (e.g., dental caries)
- Artificial hip implants (implanted medical devices)
- Subcutaneous catheters
What is Pseudomonas aeruginosa associated with in hospitals? (4)
- 16% of nosocomial pneumonia cases
- 12% of hospital-acquired UTIs
- 10% of bloodstream infections
- 8% of surgical wound infections
What is the impact of P. aeruginosa on patient mortality? (4)
- 30% deaths in immunocompromised patients
- 38% deaths in intubated patients
- 50% of deaths in AIDS patients
- 60% of deaths in burn unit outbreaks
Why are cystic fibrosis (CF) patients susceptible to chronic P. aeruginosa infections? (4)
- CF lungs contain viable bacteria despite heavy antibiotic treatments:
- bacteria are suppressed, but not eradicated in the conductive zone.
- whereas the remaining respiratory zone is protected from massive biofilm infection for prolonged time.
- Biofilms of P. aeruginosa persist
What is the impact of P. aeruginosa on chronic wounds? (3)
- Chronic wounds arise from acute wounds and require different initial treatment.
- At least 50% of chronic wounds are infected with P. aeruginosa.
- Standard techniques underestimate its presence.
Can Polymorphonuclear (PMN) leukocytes penetrate P. aeruginosa biofilms? (2)
- No, PMNs sit on top and cannot penetrate the biofilm.
- This protection is observed both in vitro and in vivo.
What is quorum sensing (QS)? (3)
- A bacterial cell-to-cell signaling system coordinating virulence gene expression.
- One bacterium produces a signal, another senses it and responds by switching on gene expression.
- QS regulates virulence and contributes to immune shielding.
How does QS affect P. aeruginosa biofilm formation? (2)
- PMNs are attracted to biofilms but cannot penetrate them.
- PMN attraction leads to collateral tissue damage & inflammation.
How does quorum sensing regulate virulence? (5)
- Cell-to-cell signaling systems composed of 2 genes.
- I gene encodes an autoinducer synthase and the R gene encodes a transcriptional activator protein (R-protein).
- Autoinducer synthase is responsible for the synthesis of an autoinducer molecule (AI), which crosses the cell membrane.
- With increasing cell-density the intracellular concentration of AI reaches a threshold level, and the AI then binds to the transcriptional activator.
- The complex R-protein/AI activates the expression of specific target genes.
What are the main QS systems in P. aeruginosa? (3)
- Las System (LasR/LasI) → Controls virulence genes (elastase, exotoxin A).
- Rhl System (RhlR/RhlI) → Controls biofilm dispersal & additional virulence factors.
- PQS System (PqsE/PqsR) → Regulates iron metabolism, pathogenesis, and QS hierarchy.
What is the Las quorum sensing system in P. aeruginosa? (7)
- LasR activates the expression of the LasI gene
- LasI synthesizes OdDHL (C12-HSL), an autoinducer molecule.
- As bacterial density increases, OdDHL accumulates.
- Increases expression of LasR (positive feedback)
- Upregulating virulence genes: Elastase, LasA protease, alkaline protease, exotoxin A, secretion systems.
- Associated with apoptosis, inflammation, and biofilm differentiation.
- Also activates the Rhl and PQS systems.
LasR - master regulator
What is the Rhl quorum sensing system in P. aeruginosa? (7)
- OdDHL acts as an autoinducer for the Rhl system, which is under the control of rhlR (analogous to lasR)
- rhlR upregulates the rhlI synthase
- RhlI synthesizes BHL (C4-HSL), another autoinducer.
- BHL accumulates with cell density and activates RhlR (positive feedback).
- Upregulates virulence genes, including: Elastase (LasB), alkaline protease, chitinase, lipase, rhamnolipids, cyanide, pyocyanin, rpoS, pilin adhesion.
- Controls biofilm dispersal.
- Regulated by LasR and PQS system.
What is the PQS quorum sensing system in P. aeruginosa? (5)
- LasR upregulates PQS system.
- PqsR (regulator), PqsE
- PqsABCDE and pqsH synthesizes PQS (a quinolone-based signal, unlike homoserine lactones).
- PQS regulates: Iron metabolism, Virulence genes (elastase, exotoxins, biosurfactants).
- Secondary regulation of the Rhl system.
How does QS deficiency affect P. aeruginosa? (3)
- Biofilms still form, but PMNs can penetrate and destroy them.
- QS is crucial for immune shielding.
- QS-deficient mutants produce less rhamnolipid, reducing PMN resistance.
What is the role of rhamnolipids in immune shielding? (2)
- P. aeruginosa biofilms produce rhamnolipids that prevent PMN penetration.
- QS-deficient strains lack rhamnolipids, making them vulnerable to PMNs.
What is the role of dynorphin A in P. aeruginosa QS? (7)
- Endogenous κ-agonists belonging to the opioid peptides
- Modulates pain and stress signals
- Found in Central Nervous System
- Contained in various immune cells
- PMNs produce and release dynorphin at sites of inflammation
- Induces PQS system which controls rhamnolipid production
- May serve as a potential therapeutic target for QS inhibition.
Explain the biosynthesis and regulation of the PQS in Pseudomonas aeruginosa.
PQS: Chelates iron, upregulates virulence factors (siderophores, T3SS, ExoS, AprX), negatively impacts denitrification, promotes PpqsA activity via PqsR-dependent & independent pathways, increases PqsE expression.
HHQ: Precursor of PQS, modified by PqsH, binds PqsR to activate PpqsA, increasing its own synthesis and PqsE expression.
HQNO: Not a QS molecule, inhibits cytochromes, aids in environmental competition, involved in respiratory pathways.
PqsR: Master regulator of pqsABCDE-phnAB operon, activated by HHQ/PQS, drives PQS synthesis & auto-regulation.
PqsE: Involved in AQ synthesis, increases virulence factors (HCN, pyocyanin, rhamnolipids, ChiC), regulates biofilm genes & MexGHI-OpmD efflux pump, negatively impacts denitrification & T6SS. Represses PpqsA activity.
Feedback process:
- Chorismic acid -> anthranilic acid using phnAB operon
- combines with octanoic malonyl-CoA -> modifications through the PqsE system to form HHQ and then PQS
- Once PQS is made, it positively upregulates the PQS regulator gene (PpqsR) and the operon responsible for the PQS production (PpqsA)
How does PQS contribute to gene regulation? (2)
- Drives AQ biosynthesis and virulence gene activation.
- Ability of PQS to contribute to gene regulation can be independent of both its ability to activate PqsR and to induce the iron-starvation response.
What is the Shield Model in P. aeruginosa infections? (2)
- Bacteria start harmless, then form biofilms. When QS is activated, they release virulence factors and a rhamnolipid shield, blocking immune responses (PMN leukocytes are killed).
- QS inhibitors block this communication, preventing shield formation. The immune system can now break down the biofilm.
What is the IQS system in P. aeruginosa? (2)
- Previously thought to be a 4th QS system.
- New research suggests it is linked to phosphate metabolism, not the QS hierarchy.
How do other bacteria compete with P. aeruginosa through quorum quenching? (3)
Some Bacillus species produce enzymes that degrade QS signals:
- Lactonase – Cleaves the homoserine lactone ring.
- Acylase – Breaks beyond the homoserine ring.
- Oxidoreductase – Modifies side groups, disrupting signaling.
