ER - Antibacterials & Drug Efflux IV Flashcards
What is the role of efflux pumps in bacterial resistance? (6)
Involved in
- Multidrug resistance (MDR)
- Quorum sensing
- Sporulation
- Virulence
- Necrosignaling
- Biofilm formation - this further exacerbates the issue of MDR due to the increased protection from antibiotics afforded by growth within biofilm matrices
How do efflux pumps contribute to biofilm formation? (3)
- Impact cell aggregation, influencing biofilm structure.
- Export extracellular polymeric substances (EPS) and quorum sensing (QS) molecules essential for communication and biofilm matrix development.
- Remove harmful substances, aiding survival in biofilms
What are the mechanisms by which efflux pumps regulate gene expression related to biofilms? (3)
Indirectly affect biofilm-related gene expression by exporting inducer molecules.
- In Gram-negative bacteria, acyl-homoserine lactones (AHLs) regulate QS and biofilm formation.
- In Gram-positive bacteria, autoinducing peptides (AIPs) trigger QS through phosphorylation cascades
What role do bacterial biofilms play in antimicrobial resistance? (4)
- Close proximity in biofilms enhances bacterial communication and cooperation.
- Supports quorum sensing (QS) and the exchange of mobile genetic elements like resistance genes.
- Biofilms stabilize plasmids, making it easier to spread resistance.
- Biofilms on medical devices pose serious risks due to their high resistance to antimicrobials.
Describe the AcrAB-TolC efflux pump’s function in antibiotic resistance (3)
- Does not affect plasmid conjugation
- Maintains low intracellular antibiotic levels, allowing the synthesis of plasmid-encoded resistance proteins.
- Critical for survival against antibiotics that inhibit gene expression (e.g., tetracycline, chloramphenicol, erythromycin, rifampicin).
What role do efflux pumps play in necrosignaling? (2)
- Upregulation of efflux pumps enhances the removal of harmful substances, such as antibiotics
- Activation of TolC after AcrA binding increases efflux pump production, with activators promoting and repressors being reduced.
How do efflux pumps help manage reactive oxygen species (ROS)? (2)
- Upregulation of genes that reduce ROS improves the cell’s ability to neutralize harmful molecules.
- This enhances survival under antibiotic stress by managing cellular damage from ROS.
What is the effect of downregulating porins in bacteria? (2)
- Downregulation reduces the production of porins, which are channels for substances, including antibiotics
- This restriction makes it more difficult for antibiotics to enter the cell and exert their effects.
What are 3 mechanisms of resistance for biofilm bacteria?
Surface Resistance: The complex structure of EPS, DNA, and proteins impedes antibiotic penetration, reducing effectiveness.
Microenvironment Variability: Differences in nutrient availability and pH lead to varying resistance levels among bacteria in different biofilm regions.
Persister Cells: Small subpopulations can enter a dormant, “spore-like” state, evading antibiotics without genetic changes, and return to normal susceptibility when conditions improve
What are the strategies for inhibiting efflux pumps to restore antibiotic efficacy? (3)
- Importance of Selectivity: Crucial for treating human infections; less critical for surface bacteria
- Proton Motive Force: Essential for both eukaryotic (e.g., mitochondria) and prokaryotic functions
- Inhibition Strategies: Focus on common methods aimed at blocking transporters that efflux antibiotics
What are the challenges in identifying efflux pump inhibitors (EPIs)? (4)
1) Efflux Pump Efficiency:
- Pumps are adept at exporting drug-like molecules, making it hard for EPIs to compete.
2) Similarity in Properties:
- Antibiotics and EPIs often share similar properties, particularly with promiscuous pumps.
3) High Concentration Requirement:
- Effective EPI concentrations can lead to cytotoxicity in human hosts.
4) Difficulty in Targeting Transporters:
- Effectively targeting these transporters has proven challenging.
What are the challenges (3) and potential benefits (1) of efflux pump inhibitors (EPIs)?
Potential Benefits: Successfully inhibiting efflux pumps could rejuvenate existing antibiotics
Challenges Beyond Human Toxicity:
- Pockets of Efflux Pumps: Large, hydrophobic, and promiscuous binding sites make targeting difficult, as they export a wide range of molecules and lack specific catalytic centers.
- Inhibitors as Substrates: Many inhibitors become substrates for other efflux pumps in the same cell, reducing their effectiveness.
- Targeting RND Transporters: For Resistance-Nodulation-Division (RND) transporters, exploring strategies to target away from the transporter itself may provide new avenues for inhibition.
What is the strategy for targeting accessory proteins of the AcrAB-TolC complex and what are the advantages? (2)
Focus on Accessory Proteins:
* Target proteins like AcrA, which link the inner membrane transporter (AcrB) to the outer membrane (TolC).
Advantages: This approach may help avoid the development of resistance against efflux pump inhibitors (EPIs).
What is NSC 60339 , what is its mechanism of action (2) and its therapeutic potential (1) as an efflux pump inhibitor?
Background:
- Originally developed as an anti-cancer drug; identified as a potential efflux pump inhibitor (EPI).
Mechanism of Action:
- Binds to a cleft between two domains of the efflux pump.
- Induces long-range allosteric effects on protein dynamics, preventing the movement and action of the efflux pump.
Therapeutic Potential:
- Could revive the effectiveness of antibiotics by reducing their export from bacterial cells via multidrug efflux pumps.
What is the mechanism of inhibition for NSC 60339 (1), effects (1) and outcome (1) of using the molecular wedge model?
Inhibitor Action:
- The inhibitor acts as a “molecular wedge” within the cleft between the lipoyl and αβ barrel domains of AcrA.
Effects on Conformational Transmission:
- Diminishes the conformational transmission of drug-evoked signals from AcrB to TolC.
Outcome:
- Reduces the efficiency of drug export, enhancing the effectiveness of antibiotics by preventing their removal from the bacterial cell.
