QS Flashcards

Question

why is inter-species communication significant?

Answer 1

increase severity of disease e.g. Non-pathogenic bacteria harboured by the host can modulate the behaviour of pathogenic bacteria pseudomonas and oropharyngeal bacteria - pPA responds to the autoinducers produced by OF and becomes much more pathogenic

Answer 2

attractive antimicrobial target

Answer 3

``` Many classes of AIs have been described to date. The most intensely studied AIs are the N-acylhomoserine lactones (AHLs) of Gram-negative bacteria, the peptides of Grampositive bacteria and a class of AIs termed AI-2, whose structures remain unknown in most cases. AHLs are usually detected through binding to and activation of cytoplasmic receptor proteins, which dimerize upon signal detection and can bind to promoter regions of target genes to activate or repress their transcription. Peptides are usually detected through binding to membrane sensor proteins of the two-component system family, although some can also be transported to the cytoplasm before interacting with their receptors. On the other hand, AI-2 binds a periplasmic protein and then interacts with either a two component system or a transporter depending on the organism. Binding to a membrane-associated sensor kinase causes the activation of a phosphorelay cascade, which results in the activation or repression of a response regulator, culminating in altered gene expression ```

Answer 4

S. aureus has multiple virulence factors and can display very rapid transmission, aiding its importance as a human pathogen. Additionally, S. aureus forms biofilms on many surfaces, including indwelling devices such as urethral stents. These indwelling devices, and subsequent biofilms formed on them, pose a serious risk for Staphylococcus infection One of the factors which contribute to S. aureus virulence is its peptide-based quorum sensing system, encoded by the accessory gene regulator (agr) locus. The autoinducer in the agr system is an autoinducing peptide (AIP), encoded by agrD. AIP is trimmed and secreted by AgrB, a membrane-bound protein. The active AIP is 7–9 aa, with a 5-membered thiolactone ring. AgrC is a membrane-bound sensor kinase to which extracellular AIP binds, leading to AgrC autophosphorylation and activation of AgrA. The agr system is intricately involved in the regulation of virulence genes, predominantly from two promoters, P2 and P3, which produce RNAII and RNAIII, respectively P2 promotes the transcription of the agr operon from the RNAII transcript, which includes agrA, agrB, agrC and agrD. Active AgrA may be a phosphorylated homodimer that induces transcription at the P2 and P3 promoters, with a higher affinity for P2 Transcription from P3 leads to the production of RNAIII, which is the effector molecule of the agr system. RNAIII is a regulatory RNA, which also functions as the mRNA for the sigma-toxin. The 5' end is thought to upregulate a-haemolysin, while the 3' end is required for the repression of protein A synthesis. RNAIII reduces the expression of surface adhesins, and increases the production of capsule, toxins and proteases. The agr system is thought to regulate over 70 genes, 23 of which are known virulence factors ``` Of the virulence factors regulated by agr, there are two classes: the first class contains virulence factors involved in attachment to the host and immune evasion ``` ``` the second class contains genes involved in the production of exoproteins associated with invasion and toxin production. It has been thought that the activation of the agr system essentially switches the bacterium from an adhesive, colonizing commensal to an invasive and aggressive pathogen ``` It is thought that S. aureus possesses two independent mechanisms of biofilm formation; the first involves an extracellular polysaccharide, polysaccharide intercellular adhesin (PIA), and the second is thought to be PIA-independent, possibly involving adhesive proteins and the sarA and agr global regulators. Because biofilms are thought to play a critical role in S. aureus infection, the role of agr in biofilm formation has been explored. When agr is non-functional, S. aureus has enhanced adhesion abilities.Therefore, when agr is not active, the bacteria remain in the first stage of biofilm formation, adhering to a surface. RNAIII is the effector of the agr system and is involved in bacterial virulence, so mechanisms to inhibit RNAIII have received considerable attention. An RNAIII-inhibiting peptide (RIP) has been found to inhibit S. aureus biofilm formation and toxin production. It is thought that by inhibiting cell–cell communication, RIP is able to prevent adherence and virulence of S. aureus.

Answer 5

P. aeruginosa is a Gram-negative bacterium capable of surviving in a wide range of environments. This organism is an opportunistic pathogen and it is commonly associated with nosocomial infections and infections of severely burned individuals, and is a leading cause of death in severe respiratory infections, such as chronic lung infections in CF patients. Infections with P. aeruginosa are difficult to eradicate, due to their high levels of antibiotic resistance and growth in biofilms Quorum sensing regulates the production of several extracellular virulence factors, promotes biofilm maturation and regulates the expression of antibiotic efflux pumps, meaning that it has a key role in the pathogenesis of P. aeruginosa. The las and rhl systems regulate the timing and production of multiple virulence factors, including elastase, alkaline protease, exotoxin A, rhamnolipids, pyocyanin, lectins and superoxidase dismutase P. aeruginosa rhlI and lasI mutants cause less tissue destruction and decrease mortality when compared with wild-type strains in multiple animal models indicating an important role for quorum sensing in P. aeruginosa pathogenesis. Apart from regulating the expression of virulence factors, some of the AIs have been shown to directly interact with host cells. 3las AI's induces interleukin (IL)-8 secretion from human bronchial epithelial cells. It also inhibits lymphocyte proliferation, downregulates the production of tumour necrosis factor alpha (TNF-a) and IL-12, and activates T cells. las AI also induces apoptosis in macrophages and neutrophils, suggesting that this molecule not only enhances the expression of virulence genes but also affects immune responses to infection

Answer 6

Bacteria communicate through the production of diffusible signal molecules termed autoinducers. The molecules are produced at basal levels and accumulate during growth. Once a critical concentration has been reached, autoinducers can activate or repress a number of target genes. Because the control of gene expression by autoinducers is cell-density-dependent, this phenomenon has been called quorum sensing. Quorum sensing controls virulence gene expression in numerous micro-organisms. As quorum sensing controls virulence, it has been considered an attractive target for the development of new therapeutic strategies.

Answer 7

AGR SYSTEM: One of the factors which contribute to S. aureus virulence is its peptide-based quorum sensing system, encoded by the accessory gene regulator (agr) locus The agr system is intricately involved in the regulation of virulence genes, predominantly from two promoters, P2 and P3, which produce RNAII and RNAIII, respectively The autoinducer in the agr system is an oligopeptide that has been termed the autoinducing peptide (AIP), encoded by agrD. AIP is trimmed and secreted by AgrB, a membrane-bound protein AgrC is a membrane-bound sensor kinase to which extracellular AIP binds, leading to AgrC autophosphorylation and activation of AgrA P2 promotes the transcription of the agr operon from the RNAII transcript, which includes agrA, agrB, agrC and agrD Active AgrA may be a phosphorylated homodimer that induces transcription at the P2 and P3 promoters, with a higher affinity for P2 Transcription from P3 leads to the production of RNAIII, which is the effector molecule of the agr system RNAIII reduces the expression of surface adhesins, and increases the production of capsule, toxins and proteases ``` Of the virulence factors regulated by agr, there are two classes: the first class contains virulence factors involved in attachment to the host and immune evasion, while the second class contains genes involved in the production of exoproteins associated with invasion and toxin production ``` It has been thought that the activation of the agr system essentially switches the bacterium from an adhesive, colonizing commensal to an invasive and aggressive pathogen BIOFILMS: One of the ways in which agr is thought to impact virulence is through its role in biofilm formation It is thought that S. aureus possesses two independent mechanisms of biofilm formation; the first involves an extracellular polysaccharide, polysaccharide intercellular adhesin (PIA), and the second is thought to be PIA-independent, possibly involving adhesive proteins and the sarA and agr global regulators When agr is non-functional, S. aureus has enhanced adhesion abilities It is thought that this role of agr is brought about by the reduction in adhesin production and an increase in the production of both d-haemolysin and proteases agr is also important for detachment of clusters of cells from the biofilm (dissemination of infection) Studies have found that agr expression varies during different steps of infection. This suggests that agr may play different roles during the course of infection and this may explain the discrepancy in some of the results regarding its role in bacterial virulence (e.g. in CF patients agr is not active) DRUG THERAPY: RNAIII is the effector of the agr system and is involved in bacterial virulence, so mechanisms to inhibit RNAIII have received considerable attention. An RNAIII-inhibiting peptide (RIP) has been found to inhibit S. aureus biofilm formation and toxin production. By inhibiting cell–cell communication, RIP is able to prevent adherence and virulence of S. aureus.

Answer 8

P. aeruginosa is a Gram-negative bacterium capable of surviving in a wide range of environments. This organism is an opportunistic pathogen and it is commonly associated with nosocomial infections and infections of severely burned individuals, and is a leading cause of death in severe respiratory infections, such as chronic lung infections in CF patients At least three intertwined quorum sensing systems and one orphan autoinducer receptor affect the ability of P. aeruginosa to cause disease LAS/RHL SYSTEMS: Two of these systems, las and rhl, rely on the production of AHLs as the signalling molecules (AIs) LAS: In the las system, N-3-oxododecanoyl-homoserine lactone (3OC12- HSL) is produced by the enzyme encoded by the lasI gene. When P. aeruginosa reaches a certain threshold density, 3OC12-HSL binds to the transcriptional activator LasR. LasR, in turn, dimerizes and binds to target promoters to control gene expression RHL: in the rhl system, the rhlI gene encodes the enzyme involved in the production of N-butyryl-homoserine lactone (C4-HSL). As with 3OC12-HSL, C4-HSL binds to its cognate transcriptional regulator, RhlR, to control the activity of target promoters The rhl system is controlled by the las system at both transcriptional and post-transcriptional levels The las and rhl systems regulate the timing and production of multiple virulence factors, including elastase, alkaline protease, exotoxin A, rhamnolipids, pyocyanin, lectins and superoxidase dismutase QSCR: Besides LasR and RhlR, P. aeruginosa encodes an orphan receptor protein, QscR, which can sense 3OC12- HSL to control its own regulon PQS: A third P. aeruginosa AI molecule, 2-heptyl-3-hydroxyl-4-quinolone (Pseudomonas quinolone signal; PQS) has also been identified. Molecules have been shown to play a role in cell–cell communication in P. aeruginosa. PqsH, which is controlled by the las system PqsR is a LysR transcriptional factor that is activated by HHQ and PQS, leading to the positive activation of many virulence factors, which include a large number of genes also controlled by las and rhl. PQS has been shown to affect biofilm formation and to regulate several virulence factors in P. aeruginosa, including elastase, pyocyanin and LecA lectin, and it is considered essential for full virulence in multiple hosts PQS can also act as an iron chelator, and both the synthesis of PQS and the activity of PqsR–PQS are involved in iron homeostasis, DISEASE: Multiple P. aeruginosa virulence factors are involved in the development of disease, including secreted factors (such as proteases) and cell-associated factors (such as lipopolysaccharide and flagella), as well as the ability to form biofilms Quorum sensing regulates the production of several extracellular virulence factors, promotes biofilm maturation and regulates the expression of antibiotic efflux pumps It has been shown that P. aeruginosa rhlI and lasI mutants cause less tissue destruction and decrease mortality when compared with wild-type strains in multiple animal models Some of the AIs have been shown to directly interact with host cells. 3OC12-HSL induces interleukin (IL)-8 secretion from human bronchial epithelial cells It also inhibits lymphocyte proliferation, downregulates the production of tumour necrosis factor alpha (TNF-a) and IL-12, and activates T cells to produce gamma-interferon. 3OC12-HSL also induces apoptosis in macrophages and neutrophils, suggesting that this molecule not only enhances the expression of virulence genes but also affects immune responses to infection Besides controlling bacterial virulence, PQS and HHQ have been shown to downregulate the host immune response through NFkB DRUG THERAPY: Natural quorum sensing inhibitors include cyclic sulfur compounds, patulin and penicillin acid Through the use of a screening system, garlic extracts and 4-nitropyridine-N-oxide were also identified as quorum sensing inhibitors These molecules specifically inhibited the activation of virulence genes by quorum sensing, reduced biofilm tolerance to tobramycin and also decreased virulence Molecules derived from the plant species Combretum albiflorum revealed that catechin has a negative impact on the production of quorumsensing-dependent virulence factors Subinhibitory concentrations of macrolides have been shown to be effective in inhibiting quorum-sensing dependent virulence macrolides are not ideal because, like any other antibiotic, excessive usage is associated with bacterial resistance

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