Quorum sensing 2016
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The document discusses the molecular basis of quorum sensing in bacterial pathogens, especially focusing on Staphylococcus aureus and Pseudomonas aeruginosa. It outlines how quorum sensing regulates virulence and biofilm formation and presents potential therapeutic approaches to inhibit quorum sensing to combat multi-drug resistant infections. Various mechanisms of quorum sensing in Gram-positive and Gram-negative bacteria are detailed, alongside the impact on pathogenicity and treatment strategies.
Quorum sensing 2016
- 1. Molecular Basis of Quorum Sensing in Virulence of Bacterial Pathogens Tuesday, May 31, 2016 1 Shezaib Siddiqui Research Fellow
- 2. Introduction What is Quorum Sensing? Molecular basis of infections a. Staphylococcus aureus b. Pseudomonas aeruginosa Biosynthesis and degradation of Quorum sensing Therapeutic approaches 2
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- 4. KEY TERMS Pathogenicity: The ability of an organism to cause a disease. Virulence: The degree of pathogenicity or disease caused by a pathogen. OR Total no. of pathogenic determinants an organism is collectively termed as virulence. 4
- 5. Phenomenon that regulates the gene expression of bacterial population in unison at particular density in response to secreted chemical molecules. OR Synchronous gene expression of bacterial population in an environment. 5
- 6. HISTORY o First Identified in late1960s by Nealson et al. o Discovered in Vibrio fischeri and Vibrio harveyii o V. fischeri is a symbiotic microbiota of Howaiian bobtail squid light organ. o V. Harveyi is a free living marine bacterium o Bioluminescence in Vibrio is control via Quorum sensing (QS). o Lux operon was discovered as QS regulatory coding region. 6 Howaiin bobtail squid Vibrio fischerii Vibrio harveyi
- 7. Quorum Sensing in a Nut Shell Production and release of signalling molecule (Auto inducer). Diffusion of Auto inducer (AI) molecule at low cell density leaving the QS circuit in-active Activation of QS circuit by AI at higher concentration due to Higher cell density. Transcriptional activation of down regulating genes by AI receptor complex or other activated signalling molecule. Activation of virulence, biofilm formation, sporulation, competence and antibiotic production. 7
- 8. QS IN GRAM NEGATIVE BACTERIA The autoinducers are typically molecules called acyl- homoserine lactones (AHLs). AHLs diffuses extracellular and intracellular via passive transport. QS IN GRAM POSITIVE BACTERIA The autoinducers are oligopeptides, short peptides typically 8-10 amino acids long. Oligopeptides excretes in extracellular environment via active transport. 8
- 9. Schematic Representation of QS Circuits Canonical bacterial quorum-sensing (QS) circuits. Autoinducing peptide (AIP) QS in Gram- positive bacteria by (A) two-component signalling, or (B) an AIP-binding transcription factor. Small molecule QS in Gram-negative bacteria by (C) a LuxI/LuxR-type system, or (D) two- component signalling. Gram positive Gram negative
- 10. QS Circuit of Vibrio harveyi Lux Bioluminescence System
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- 13. S. aureus is a gram positive opportunistic pathogen. Causative agent of many cumbersome respiratory and skin infections and poisonings. Few of high mortality infections and poisonings are Scalded skin syndrome, toxic shock syndrome, furuncles, carbuncles, sinusitis, otitis media etc. Emerged as Multi drug resistant bug and many hospital setting. Prevalent in > 60% of Nosocomial infections MRSA has mortality rate of >20% 13
- 14. Encode various virulence factor under the control of Quorum sensing system (Agr operon) 14 Scalded Skin Syndrome Impetigo Toxic shock syndrome Otitis media
- 15. S. aureus has a peptide based quorum sensing system ,encoded by accessory gene regulator (agr) locus. The agr locus controls transcription of two RNA transcripts RNA II and RNA III from promoter P2 and P3, respectively. RNA II encodes Agr A, B, C and D proteins RNA III encodes δ-hemolysin and posses regulatory activity. 15 Protein Function Agr A Transcription factor (Activated by Agr C) Agr B Triming and transport of pre- AIP (Agr D) Agr C Histidine Kinase recetor of AIP Agr D Pre- Auto inducer peptide Table 1: components of agr system
- 16. The Agr System 16 QS Circuit of Staphylococcus aureus
- 17. Role of RNAIII in virulence: 5’ end upregulates transcription of α- hemolysin. 3’ end is responsible for the repression of rot (repressor of toxin) protein and Protein A. Rot inhibits the transcription of various toxins. Inhibition of rot upregulates the translation of toxins and increases virulence. Repression of Protein A (cell surface protein) decease adhesion of biofilm. 17
- 18. Role of Agr in Biofilm control: Agr A up regulates the translation of PSMs (Phenol soluble modulins). PSMs are peptide toxin that help in channel formation in tissues. PSMs also acts as surfactants that allow biofilm dispersal. Biofilm dispersal helps S. aureus to colonize and infect new sites. 18
- 19. Polymorphism in Agr Locus S. aureus can be classified in to 4 distinct groups based on Agr locus. 19 Agr locus Agr I Agr II Agr III Agr IV
- 21. P.aeruginosa is a Gram-negative opportunistic pathogen. Responsible for severe nosocomial infections cellulitis, UTIs, endocarditis and epidermidis bullosa. Accounts for more than 10% of nosocomial infections. Patients with Cystic Fibrosis, injuries (especially burns/boils) are highly susceptible to P. aeruginosa infections. Second leading cause of ventilator associated pneumonia. Difficult to treat due to emerging drug resistance. 21
- 23. 23 • Three QS circuits are identified • LasI/R (3-0C12HL synthase/ Receptor) • RhlI/R (C4HL synthase/ Receptor) • Pseudomonas Quinolone Signal (PQS) Las Inducer/Repressor (I/R) system: • Auto-induced by LasI • Controls RhlR operon • Activates transcription of Las B (Elastase), LasA (Protease), tox A (Exotoxin A) and aprA (alkaline phosphatase). • LasI inhibits Rhl R.
- 24. RhlI/R system: Upregulates rhl I ◦ Positive regulator of Las B (elastase), RhlA and B (Rhamnosyl transferase), RpoS (Stationary phase σ factor) and Pyocanin (niche molecule) 24
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- 26. Negative regulation NFκB. Induces apoptosis in macrophages. Down regulates TNF-α and IL-12. Induces IL-8 from human bronchial epithelial cells. 26
- 27. Biosynthesis and degradation of Acyl Homo serine Lactones 27 Fatty acid pathway AHL synthase
- 28. 28 Types of Auto inducers in gram negative bacteria PAME= propionyl amphotericin B methyl ester, DSF= Diffusible signal factor, THMF= tetra hydroxyl methyl furan
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- 30. Novel therapeutic tartest against multi drug resistant bacteria. Reported to decrease virulence only, thus empower host immune system to combat attenuated pathogen. Low chances of drug resistance against quorum quenchers as they do not kill bacteria. 30
- 31. Strategies for Quroum Sensing Inhibition 1. Elimination of signal By stimulating enzymatic degradation of auto inducer By inhibition of auto inducer biosynthesis and receptor molecule biosynthesis 2. Inhibition of signal receptor complex By using auto inducer analogues By treating with antibodies against auto inducer 31
- 32. Current Approaches for QS inhibition AHL acylases, paraxonases and AHL lactonases are secreted by many bacteria to degrade AHL , therefore negatively control QS. AHL and AIP analogues have been synthesized to inhibits QS in S. aureus, P. aeruginosa and other pathogens Synthesis of inhibitor molecules against enzymes involved in AHL biosynthesis, eg: tricolsan inhibits enoyl-ACP reductase. Inhibition of auto inducer receptors by using RNAi technology. 32
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- 34. 34 Auto Inducer and Inhibitors of P. aeruginosa
- 35. 35 Auto inducers and analogue Inhibitors of S. aureus s
- 36. QS circuits serve as new and potential anti virulence target to control infections with reduces risks of resistance evolution. 36
- 37. Miller, Melissa B., and Bonnie L. Bassler. "Quorum sensing in bacteria."Annual Reviews in Microbiology 55.1 (2001): 165-199. Waters, Christopher M., and Bonnie L. Bassler. "Quorum sensing: cell-to- cell communication in bacteria." Annu. Rev. Cell Dev. Biol. 21 (2005): 319-346. Whiteley, Marvin, Kimberly M. Lee, and E. P. Greenberg. "Identification of genes controlled by quorum sensing in Pseudomonas aeruginosa."Proceedings of the National Academy of Sciences 96.24 (1999): 13904-13909. Bassler, Bonnie L. "How bacteria talk to each other: regulation of gene expression by quorum sensing." Current opinion in microbiology 2.6 (1999): 582-587. Yarwood, Jeremy M., et al. "Quorum sensing in Staphylococcus aureus biofilms." Journal of bacteriology 186.6 (2004): 1838-1850. Rutherford, Steven T., and Bonnie L. Bassler. "Bacterial quorum sensing: its role in virulence and possibilities for its control." Cold Spring Harbor Perspectives in Medicine 2.11 (2012): a012427. 37
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Editor's Notes
- #10: Canonical bacterial quorum-sensing (QS) circuits. Autoinducing peptide (AIP) QS in Gram-positive bacteria by (A) two-component signaling, or (B) an AIP-binding transcription factor. Small molecule QS in Gram-negative bacteria by (C) a LuxI/LuxR-type system, or (D) two-component signaling.
- #26: In P.aeruginosa at least three interwined quorum sensing (QS) system and one orphan autoinducer receptor affect the ability of this organism to cause disease.