Bacterial Diseases and Quorum Sensing

Abstract

The bacteria require communication among themselves in order to survive and to establish communities. This is especially so in the case of biofilm formation, which is one of the most resistant mechanisms of bacterial survival. Bacteria have been using these biofilms in the production of various toxins and in protecting them from the aggressiveness of the environment where they establish. The quorum-sensing mechanism is the method of communication between the bacteria, which is now being utilized to create medicines that prevent the formation of biofilm. With more understanding of this chief mechanism, it is hoped that bacterial resistance through the use of antimicrobials can finally be controlled.

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Researches in molecular biology have revealed many of the hidden mechanisms of the cell and the living organisms. With advances, the researchers are now able to understand the complex mechanisms that each organism uses to survive in a hostile environment. The biggest implication of these discoveries is in health care, which is currently under attack by the huge number of microorganisms that are gaining resistance to the antibiotics and drugs that we are producing. In order to protect human beings from falling prey to these small yet deadly organisms, we must be able to identify the mechanisms that help them operate and gain virulence, among other things.

It is now well known that bacterial infections cause infection by forming communities and biofilms. In contrast to the past concepts, these biofilms and communities are highly organized, and work together for each other’s mutual benefit. Such a community-organized thinking pattern is a relatively new discovery for researchers and a subject of intense interest. Quorum sensing is among the methods that are used by bacteria to communicate and thereby increase their virulence and population strength. The article is a review of the literature regarding quorum sensing, the various discoveries in this area, and the implications for the health care sector. (Current Opinion in Biotechnology, 2004) The evolutionary realization of these microorganisms to work together to increase their survival chances is now apparent in the form of colonies and biofilm formation. This enables the communities to migrate to new environments, search for better nutritional supply resources, and create biofilms to protect the bacteria from external insults. (Keivit and Iglewski, 2000) Now the role of auto-inducers in the various community responses and reactions is well understood, and quorum sensing has become known as one of the chief methods of communication among the bacterial populations and communities.(Keivit and Iglewski, 2000)

Introduction to Quorum Sensing or Cell to Cell Communication

For a bacterium to survive in the highly hostile environment it comes across with, it must be able to adapt to various challenges quickly. Most of the bacteria are present in groups and therefore are present in near vicinity to each other. Groups are essential as they provide the bacterium with the necessary information regarding its environment, and help it to anticipate the future needs. The group strategy tries to establish contact with each other and tries to coordinate its objectives and various actions so as to help each other survive better. (Fray, 2002)

Quorum sensing is the mechanism of communication between various bacteria in order to ensure their survival within the host or environment and from other bacterial colonies. Quorum sensing is somewhat a recent discovery of the social patterns of the bacteria. Other social patterns that have been identified include swarming motility, conjugal plasmid transfer, antibiotic resistance, biofilms maturation and virulence (Diggle, Crusz and Camara, 2007). The social survival mechanism requires the bacteria of the same kind to work in harmony and create a collection or community in the local environment. With this collection, the signals produced via the various molecules accumulate in these communities. The signals are beneficial in many ways for the community. They contribute to the production of varying bacterial responses and help in competing and resistance from other bacterial communities that may try to establish themselves in that area. The signal accumulation however, is seen in rather large groups of bacterial accumulations, mostly biofilms. This phenomenon has been termed as the quorum sensing phenomena. (Current Opinion in Biotechnology, 2004) In other words, with the help of the signaling molecules, the bacteria are able to function as a single unit, and coordinate their actions in order to survive in the local environment. (Diggle, Crusz and Camara, 2007)

In concise wordings the functions of the quorum sensing mechanisms are “to regulate competence development, sporulation, antibiotic synthesis, virulence factor induction, cell differentiation, nutrient flux with other physiological events in pathogenic bacterial infections” (March and Bentley, 2004) Quorum species is also thought to relate interspecies formation between symbionts and competitors. A good symbiotic relationship will show complex patterns which are highly organized and where the products of one community may be of benefit to the other. Of such is an example of bacterial plaque that establishes itself on the human teeth.

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This quorum sensing can be seen in prokaryote-prokaryote and prokaryote-eukaryote interactions. While in many cases, these quorum systems may be used synergistically to help the various species grow, on the other hand, the same systems can be used to prevent the growth of the other species. These enzymes that are involved in disarming the opposing species quorum sensing molecules are known as quorum quenching enzymes. These enzymes have been associated with many other phenomena, including anti-pathogenic and signal interference. It is widely known that AHL is the prime quorum sensing product of the bacteria. It has been demonstrated that AHL lysing enzymes, or AHL acyclase is produced by many bacteria.(Dong and Zhang, 2005) Other similar enzymes for lysis of AHL and similar quorum sensing enzymes are also produced by a variety of species. This creates many possibilities for the researchers, who are aiming to prepare such harmless cultures and introduce them as defense mechanisms for the prevention of biofilm formation within the body. The huge variety of quorum quenching enzymes is now being discovered. Among these are included AHL lactonase, AHL Acyclase, lactonase and acyclase I. (Dong and Zhang, 2005)

The eukaryotes have also devised methods to create quorum quenching enzymes. There are two types of enzymes that have been reported to be produced by eukaryotes. First is L-homoserine and acylase I. (Dong and Zhang, 2005) Among the most studied of the eukaryotic species are the fungi, which show some very similar and yet dissimilar patterns of quorum sensing. What they do establish however, is that quorum sensing may not be limited to bacteria alone, and that higher life forms may have evolved some of these systems themselves.

The Nature of Bacteria and Biofilms

Before understanding quorum systems, it is necessary to understand the environment and the nature of the bacteria that show these feature.For bacteria to survive in nature, they need to build close relationships with species of their own kind. If these bacteria are occupying the same habitat, then they are termed as a community. The microorganisms create a biofilms in the community, which comprises of many molecules and substances apart from the bacteria forming it.(Percival and Bowler, 2004). The first bacteria that adhere themselves to the surface of any compatible surface release certain substances to attract the attention of the bacteria of similar species. This method of communication is essentially quorum signaling. (Biosignals, 2007)The biofilms formed are able to increase the potency of any action that they choose to take.

This is especially the case in medicine, where the formation of biofilms and communities of bacteria lead to infection and diseases within the human body. It is not necessary that each production that is signaled via the quorum sensing is detrimental to the host; however, the production of toxins does take place through such systems, and therefore the risk of infection remains. In this light, area of major concern in medicine is of surgical wounds and their infection by such bacteria.(Percival and Bowler, 2004) While initially, the species may be limited to only one, with the gradual growth of the biofilms and the synergism of various organisms, a complex community can evolve. Thus the pioneering bacteria will help in the initial colonizing of the infection or wound site, where as the subsequent bacteria will build upon these, help in developing an ecosystem and in the progression of the biofilms. This creates havoc for the host and the healing wound, which are affected negatively. (Percival and Bowler, 2004)

However, there are theories that question the role of biofilms in chronic wound cases. It has been demonstrated that chronic wounds do contain bacterial biofilms. However, the current topic of debate is finding methods to prevent this biofilm formation at such sites. The researches have shown that lactoferrin secreted by the human body is very effective in preventing biofilm formation. It can also destroy and disrupt the already formed biofilms on the wound. This is because lactoferrin encourages the cells to float and establish the planktonic form instead of the biofilm and community form. The use of lactoferrin is therefore now being considered as helpful in reducing biofilm formation. (Mertz, 2003)

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There are many theories regarding the nature and origin of the biofilms. Most of these biofilms are enclosed in a matrix, which is attached to a suitable ecosystem. For the biofilms to survive, this ecosystem must be able to provide a good nutrition source to the bacteria, and must be in an aquatic medium.(Donlan and Costarton, 2002) Most of these biofilms are resistant to conventional method of bacterial removal, and indeed hold a very strong potential for developing resistance against different antimicrobials. (Biosignal, 2007) Not all bacteria go ahead and make biofilms, and this is what separates them from the free floating planktons. Therefore, the formation of the biofilms is a characteristic of particular series of bacteria. These bacterial films are present within all ecosystems, and have the ability to establish themselves wherever a suitable environment is found. So while medicine is one area where biofilm production is a concern, other non medical areas such as water lines and water resources are also apt to suffer significantly from these biofilms. These biofilms cannot survive unless they develop mechanisms to resist themselves from various physical and chemical insults and agents. It is this resistance that gives rise to the questions about how these unicellular organisms communicate between each other. (Donlan and Costarton, 2002)

Therefore, a current biofilm definition would include these features.

  • Microbial sessile community
  • Irreversibly attached to the stratum or interface or to each other
  • Matrix comprising of extra-cellular polymeric substances
  • Production of an altered phenotype with respect to growth rate and gene transcription.
  • The non-biofilm variety is mostly seen on agar plates as widespread bacteria showing none of the above mentioned traits. (Donlan and Costerton, 2002)

While in the past, the biofilms structures of these bacteria were considered random, recent researches have negated this view. A mixed species biofilm shows a heterogeneous structure and micro-colonies of individual bacteria within the biofilms. 15% of the biofilm is composed of cells, while 85% is composed of matrix material. The cells are located within matrix-enclosed towers and mushrooms, which contain open water channels in between them. Such biofilms are designed to allow flow of water within the biofilm. (Donlan and Costerton, 2002)

What is now known is that bacteria behave in a different manner when they start making a biofilm, and change their phenotype and pattern of behavior. With the help of quorum sensing, the bacteria are able to adapt and respond to favorably to the environmental challenge they are put up with. One of the most significant outcome of this quorum sensing is the change in the genetic expression of the cells. If the bacterial colony is faced with chemical or physical threats, the bacteria signal each other to reduce their activity and enter into a slow quessent state. The slow growing state reduces the efficacy of the antimicrobials or other chemical agents. It is now known that while the bacteria in their planktonic form may be susceptible to a certain antibiotic, they may not be significantly affected by the same if are configured in a biofilm. This resistance can be as high as 50 to 1000 times more than in bacterial biofilms than in the free flowing state. (Mertz, 2003)

Substances Used for Quorum Sensing According to the Bacteria Type

Many bacteria retain the ability to produce auto-inducers and thereby retain quorum sensing abilities. But for each type the auto-inducers can be different. So far, the biggest method of classifying the quorum sensing agents is done via the gram negative and the gram positive bacteria. In gram negative bacterial species, the most common quorum sensing agent is the N-acyl homoserine lactones or AHLs. This molecule at high concentration activates the R protein, which in turn activates the target genes. AHL has been found to be the most common signal used by gram negative bacteria, however other signals also exist. Some of these include 3-hydroxypalmitic acid methyl ester, diffusible extracellular factor of DSF, pseudomonas quinolone signal or PQS, and diketopiperazines or DKPs. (Keivet and Iglewski, 2000)

In gram positive bacteria however, the quorum sensors are different. In contrast to the AHLs that are so commonly secreted in the gram negative bacteria, no gram positive bacterium has shown the production of this molecule. Mostly in gram positive bacteria is the production of peptide signal molecules. These mainly consist of RNA II and RNA III operons. Other substances also play a role such as sar gene product or SarA. (Keivet and Iglewski, 2000)

The signals in gram positive bacteria utilize oligopeptides. These are detected via two component phosphorelay proteins. The receptor in these cases is usually a membrane spanning histidine kinase, however, it may be a cytoplasmic phosphatase. Another receptor type is the transcriptional repressor, but other variations can also be found. (Sprague and Winans, 2006)

Gram negative bacteria have shown a larger presence of the AHL quorum signals, as were discovered in the Vibrio fischeri. The acyl chain in the various AHLs produced from various bacteria can be of different lengths, which can be four to 18 carbons in length. However, AHLs are mostly limited to those bacteria that are dependant on the quorum signaling in order to colonize a plant or an animal. But AHLs are not the only quorum produced signals in the gram negative bacteria. Another type of signal used by these bacteria is the AutoInducer-2 or AI-2, which is mostly found in many of the eubacteria. As opposed to the AHLs which are synthesized by LuxI/ LuxR pairs, AI-2 is produced by LuxS. This signal has been found to have a very divergent role in each bacterial species. (Sprague and Winans, 2006)

Requirements of Quorum Sensing Signals

Many molecules are produced by bacteria but not all are considered as quorum sensing signals. Certain requirements must be met before a molecule will be termed as such. Quorum sensing signals are produced at very specific times and due to very specific situations. Therefore, a quorum sensing signal will be produced during a particular phase of the growth cycle or due to some environmental changes. (Diggle, Crusz and Camara, 2007) These signaling molecules must be able to produce a reaction in the bacterial population which is unique from the normal behavior they would produce when independent to the community.(March and Bentley, 2004) The quorum sensing signals are released extracellularly, and the receptors are located outside the cell membrane. Therefore, in order to be called a quorum sensing signal, the cell must produce the quorum sensing signals and must bind to specific receptors. The third requirement is that a certain quantity or threshold level of the quorum signal must be present, and this in turn must cause a coordinated response in the bacteria. And finally, “the cellular response should extend beyond the physiological changes required to metabolize or detoxify the molecule. (Diggle, Crusz and Camara, 2007)

The Details of Quorum Quenching Enzymes

There are certain features of the quorum quenching enzymes that are found in almost all types. The structure is composed of homoserine lactone moiety, which of various lengths and substitutions of the acyl chains. Of such enzymes are included the lactonase and decarboxylase. The AHL acyclases break the amide linkage between the fatty acid chain and homoserine lactone moiety. (Dong and Zhang, 2005) Another family of quorum quenching enzymes is the mammalian paraoxonase family. These comprise of three types of enzymes, PON1, PON2, and PON3. Many other enzymes are being discovered with quorum quenching abilities and these can be used in medicine for the prevention and disruption of biofilms. (Dong and Zhang, 2005)

History of Quorum Sensing and Its Development

The quorum sensing phenomena was first demonstrated in Vibrio fischeri. This is a symbiotic species which provides light to its marine eukaryotic hosts. (Lerat and Moran, 2004) However, light emission is based on the density of the bacteria and the resultant release of auto-inducers, in this case the AHL. This AHL production is dependant on the Lux1 gene. This species became the basis of comparison for further experiments. It was later proved that the quorum sensing mechanism in this species was very much similar to other quorum sensing and producing bacterial species. The roles in each bacterium started to differ, and the presence of multiple factors apart from the quorum system in the cell to cell signaling mechanism started to come to light. One of the most studied cases was of Pseudomonas aerugenosa. This organism is known for its high virulence and two separate systems for quorum releasing. Research is still underway in identifying the complex mechanism in this organism.

The other bacteria that were then studied included plant pathogens Erwinia carotovora and Agrobacterium tumefaciens.(Lerat and Moran, 2004) Each bacterial species has shown some level of evolutionary history that has taken place during the years. Some bacteria have been devoid of the Lux1/R systems, some have other autoinducers apart from the AHL, and in some, the function is limited to only regulatory pathways. The evolutionary development of the quorum sensing mechanism was also revealed by the presence of mixed locations of the genes, which show the potential for loss or horizontal transfer. These evolutionary mechanisms are very much indicative of the constant evolutionary changes that may be taking place, and which can help identify ways to prevent bacterial resistance. The analysis confirms that quorum sensing is a mechanism that is as old perhaps the bacteria themselves. Horizontal transfer tendencies have also been established, further confirming the role of genetic heredity. (Lerat and Moran, 2004)

Identification of the Molecules Involved in Quorum Sensing

Quorum sensing researches are currently working towards identifying various molecules that work as communication pathways for the bacteria. By blocking them prior to their aggregation and increase in virulence, the researchers hope it will prevent many lethal infectious diseases from occurring. (Segelken, 2002) Many molecules are now being identified. For example, Agrobacterium tumafaciens was among the first of the bacteria to be studied for quorum sensing. The protein identified as the quorum sensing protein for this bacterium is the A. tumefaciens TraR protein, in complex with its pheromone N-3-oxooctanoyl-L-homoserine Lactone (OOHL). Pheromone is a terminology used to describe the nature of the chemical signaling resembling those in insects. While the discovery of quorum sensing bacterium was found in Agrobacterium, there is still more research required for Pseudomonas species, which is raising questions about possibility of other mechanisms involved. (Segelken, 2002)

The AHL is among the most commonly produced quorum sensing substances by bacteria. While all may produce the same substance, the activity and the role played by the same molecule in each bacterium may differ. The enzymes that produce the AHL are mainly categorized into three types. These are the Lux 1, Lux M and HdtS respectively. Lux 1 type is the most common type found as well as produced. The AHLs have been found to be produced in both plant and animal invading bacteria. (Fray, 2002)

The Complex Mechanism of Quorum Sensing as Seen in the Case of Pseudomonas Species

Researches in pseudomonas species has revealed a much more complicated system of quorum sensing and the various mechanisms that dictate it. It is known that there are two quorum systems that operate in the expression of genes in the pseudomonas. These two systems are LasR-LasI and RhlR-RhlI respectively, both of which are acyl homoserine lactone or AHL quorum sensing systems. Since pseudomonas is an opportunistic organisms, many of the genes cannot be studied in vitro, and therefore, the quorum effects studied in the laboratories alone can be limited.

Can Quorum Sensing Be Expected in the Fungal Species

Interest is increasing in the possible role of quorum sensing in the fungal species along side bacteria. The quorum sensing in the eukaryotic life form has been theorized, but not been established fully. Still there are certain features that point towards this trend, or at least the evolutionary relevance to the bacterial precursors. (Sprague and Winans, 2006) This mechanism was first to be found in the fungus Histoplasma Capsulatum a soil fungus in the saprophytic form. Although in nature, this fungus is present in the filamentous forms, it is known to turn into the yeast form once it enters the human body. In a density dependant fashion akin to the bacterial, the fungus or the yeast produces various unique cell wall polysaccharides. This factor is considered as an important part of the virulence of the fungus. Such a density dependant phenomena is very much reminiscent of the quorum sensing density dependant production.(Sprague and Winans, 2006) There are many other examples that have come to light in fungi showing the same phenomena. These include Ceratocystis ulmi as well as Candida albicans. However, the density dependant phenomenon is the only one that has been considered similar to those of bacterial quorum sensing mechanism. Other similarities have yet to be identified in this area. Fungal quorum sensing however, does demonstrate a morphogenetic transition. There are many other areas that need to be understood before the true quorum sensing patterns in the fungi can be identified. (Sprague and Winans,2006)

Medical Relevance of Biofilms and Quorum Sensing

It is now believed that around 65% of the infections in the human body arise from the bacterial biofilms that form within the body. This is especially true for infections of lungs, urinary tract, and persistent wounds and periodontitis and caries development. These bacteria can be easily transmitted to other human beings, and the costs of creating antibiotics for this purpose are very high. (Biosignals, 2007)

While quorum signaling and biofilm formation is considered as a negative aspect of bacterium species, it can be used to advantage in many cases. Certain bacteria can in fact provide a protective role by forming a biofilm and thereby preventing the formation of other exogenous and pathogenic bacterial films. The normal flora of the hair follicles and the skin are some of the examples of the bacteria providing protection to the body. (Mertz, 2003)

Quorum Sensing in Clinical Practice: The Case of Staph Aureus Infections

It is now well known that in order for the bacteria to survive in an ecosystem, they must work together and live in communities. Most of the communities made are actually biofilms, and these films in the medical practice are very difficult to get rid of. Apart from that, these films do not respond adequately to the antibiotics. (Serralta et al, 2001) Biofilm formation and resistance is of main concern among clinical settings due to the rapid increase in the number of resistant microorganisms. The result is severe uncontrollable infections, with poor prognosis, which have a very high virulence. Among such is the resistance of staphylococcus aureus species. Methicillin resistant staph aureus cases are continuing to increase rapidly, and are now a major pathogen in nosocomial infections as well as urinary tract infections.(Ando et al, 2004) These bacteria are increasing their resistance via the biofilm formation. The various substances that help in biofilm formation include the polysaccharide intracellular adhesion or PIA, and the alpha toxin. With the ability of the bacterium to adhere to many types of matrix, the initiation of the biofilm is very easy for these bacteria in a variety of body locations. These bacteria have shown a very strong component of quorum sensing in their establishment, their resistance as well in their virulence and propagation. Therefore, it has been suggested that any mechanisms that are able to block quorum sensing can in turn block the activity of the methicillin resistant staph aureus biofilms, and can help prevent infections and disrupting them. (Ando et al, 2004)

It is now known of the role of bacterial accessory genes in the pathogenesis or the virulon of the disease. This expression of virulon in the staph aureus is controlled by the Agr complex, comprising of two transcription units. Since Agr expression is density dependant, therefore, it has been termed as the quorum sensor for staphylococcal aureus. (Wright, Jin and Novick, 2005) This however, is a simple explanation of the complex quorum sensing mechanism that has involved in staphylococcus alone. In staph aureus only, the agr locus has four specific groups, while in non-staph aureus groups, these amounts to almost 20. The divergence is due to the activity of the AIP, which are heterologus in nature and therefore have the ability to block the activity and quorum sensing of bacteria in vivo. This ability has been especially seen in cases of abscesses, which under normal circumstances and under no impedance would mature within 2 to 3 days. The application of the AIP has shown to inhibit the activity of the bacteria and therefore prevents the infection as well as abscess formation. (Wright, Jin and Novick, 2005) By understanding the mechanism of staph aureus activity, it is easier to predict the course of events and therefore interfere at the stages prior to the development of the biofilm and infection.

The researches have shown the initial rapid activity of the infecting bacteria is within the first three hours, at the time when agr is activated and toxic exoproteins are produced. In the abscess formation, the next phase is of neutrophil infiltration of 1 to 2 days, when the abscess matures itself. (Wright, Jin and Novick, 2005) This is followed by reactivation of the bacterial activity, which had become dormant during the infiltration phase. API administration has been seen to block this progression of abscess formation even with a single dose. The application of the API in the early phases of the wound is essential as it can provide the body with the first line defense against the bacteria. Bacteria are the most active in the initial three hours, at the time when the body is not able to generate a rapid response. (Wright, Jin and Novick, 2005) This means that until the body is able to start defending itself, the bacteria have already established themselves. It is at this stage that the API or other quorum sensing inhibitors can be especially useful to provide protection to the body and prevent the formation of the abscess. These and other researches are helping identify the key players in the staphylococcal infections, which are increasing alarm in the medical field. (Wright, Jin and Novick, 2005)

Biosignal Technology

Of the recent innovations, the use of biosignal technology holds much promise. This technology aims the destruction of the biofilms in a different manner. it aims to disrupt the biofilms, in contrast to the chemical treatment and antibiotic use for bacterial destruction. The technique will prevent the formation and emergence of resistant strains of bacteria, already a severe problem in the medical world. (Biosignal, 2007) With the formation of the anti-biofilm compounds, the bacteria are unable to adhere to various surfaces and are prevented from forming biofilms. There are wide applications for this technology, including medical, such as contact lenses, valves and cathetors etc, to non medical, such as pipelines and water supplies. (Biosignals, 2007)

Introduction of Ribonucleic Acid Iii Inhibiting Peptide

The role of ribonucleic acid III inhibiting peptide is among the new researches in the area of quorum sensing and biofilm development. Research carried out by Stoodley et al, evaluated the role and efficacy of Ribonucleic acid III inhibiting peptide in preventing biofilm formation in implantable medical devices. Mostly two bacteria are involved in the formation of biofilms in such devices. (Stoodley et al, 2005) These are staphylococcus aureus and epidermidis. These bacteria initially form a biofilm and later on produce toxins which lead to systemic infection within the body. Ribonucleic acid III inhibiting peptide is a quorum sensing inhibitor, which has been shown to prevent graft infections from taking place. It has been found to be effective in controlling the formation of biofilms, enhancing the effects of the antibiotics to greater degrees. It has also been seen to increase the efficacy of cationic peptides in the removal of normal recalcitrant biofilm infections.(Stoodley et al, 2005) Stoodley’s research reached the conclusion that ribonucleic acid III inhibiting peptide is among the most useful substances in preventing staphylococcal infections in clinical settings. This along with the safe profile makes it an ideal material to coat medical devices with.

Other Materials for the Reduction of Quorum Sensing in Bacteria

Apart from lactoferrin, biosignal technology and RNA III inhibiting peptide, certain other enzymes are also being implicated for blocking quorum signaling. Enzymatic debridment has been successfully used in various surfaces such as stainless steel, contact lenses, polypropylene etc. The enzymatic debridment has been found to be effective for both gram positive as well as gram negative bacteria. (Mertz, 2003) Exposure to DNAse I enzyme has been seen to prevent matrix formation of a biofilm. Drugs such as erythromycin are showing efficacy against chronic upper respiratory tract infections due to biofilm formation. The combination therapy of roxithromycin and imipenim has been especially successful for treating resistant infections of staphylococcus aureus biofilm infections. These drugs help invasion of the biofilm with the leukocytes. (Mertz, 2003)

Applications of the Quorum Sensing Technologies

One of the most debated applications of the system is in the treatment of methicillin resistant staphylococcal infections. These strains have been found to be susceptible to the RNA III inhibiting peptide. The RNA III inhibits with the gene locus agr, which is responsible for staphylococcal toxicity. This technique has shown enhanced activity of the antibiotic when used in combination. The quorum sensing technique is expected to be a very good method for reducing the infections through resistant bacteria, and improve clinical outcomes. (March and Bentley, 2004) Another research has shown a promising role of RIP in the prevention of biofilm formation, which is specially an issue in grafts and in medical devices that are inserted in the body. Since the biofilms are resistant to antibiotics, the risks of morbidity and mortality are high. RIP however, is needed to be administered in multiple dosing, indicating a dose dependant relationship. RIP has been shown to augment the activity of the antibiotics like teicoplanin in the reduction of antimicrobial activity. RIP therefore is one of the expected therapeutics that can be used to prevent antibiotic resistance. (Balaban et al,2007)

Quorum sensing is showing exciting promise in recombinant gene products and in metabolic engineering. It is now widely being used to regulate gene expression and control cellular growth. (March and Bentley, 2004) Pharmacological companies are also now looking at various substances and methods that can block quorum sensing mechanisms in the bacterial cells, thereby preventing the production of bacteria biofilms. The introduction of the halogenated furanone compounds have shown good anti fouling and antimicrobial properties. However, it is being currently used on the marine plants. Furanones are essentially compounds that have been produced by the eukaryotes to prevent biofilm formation on their surfaces. Furanones have been found to be made by a marine algae D.pulchra.

These furanones have shown to reduce the formation of biofilms of the surfaces of these algae and thereby protecting the plant. So far the true abilities of this compound have not been completely evaluated. (Hentzer and Giskov, 2003) What is known however is that pure form of this compound has not been active against the quorum sensing systems of P aeruginosa. Experimental research has shown that some derivatives of the compound were able to affect the quorum sensing abilities of the P aerugenosa. Research has also shown that furanone compounds may be equally effective against biofilms. Such researches are pointing to a very strong possibility that bacterial biofilms can be prevented by other means other than the conventional antimicrobial therapies. Since P aeruginosa, and various staphylococcal species are among the most virulent and antibacterial resistant organisms, the researches carried out can help reduce the creation of further resistant species. (Hentzer and Givskov, 2003)

Potential of Vaccines in Preventing Staph Aureus Resistant Infections

New researches are now looking at methods to introduce vaccines that help prevent bacterial resistance. These vaccines are specifically being designed to disrupt the bacterial quorum sensing abilities.(Scripps Research Institute, 2007) This helps keep the bacteria in their harmless states, while at the same time, allows the body time to combat the infection and bacteria at its own pace. The researchers are currently producing various haptens that are made according to the structure of the autoinducers produced by the bacteria. These haptens can be conjugated with specific proteins within the body, and can help initiate the generation of antibodies from the immune systems. As a passive vaccine, these haptens can be introduced within the human system, and give the immune system the needed information to start resisting bacterial attacks. The active form has been implicated in cases which may be undergoing surgery and are under risk of infection. (Scripps Research Institute, 2007)

Conclusion

Quorum sensing is among the most researched fields in microbiology due to the tremendous impact it can have on many fields that come under it. Bacterial biofilm production is a problem that is causing high cost consumptions in medicine as well as research areas. The identification of the mechanisms that lead to the formation of the biofilms and ways to prevent them can help save these costs. In medicine, biofilms have the potential to form almost anywhere. These can include either water or sewerage lines, or in surgical wounds and chronic lung infections. Removing these biofilms and treating infections of biofilms are costly as well as time consuming with no significant results. Biofilms are very resistant to chemical and antibacterial agents, and production of toxins from these films can lead to significant morbidity and mortality in plants and animals alike. With the emergence of methicillin resistant staphylococcal aureus infections, the antibiotics are not effective in controlling these diseases, increasing the risk of morbidity and mortality.

Quorum sensing technologies can be very helpful in identifying the processes of virulence and disease procession. With this method, it is hoped that bacterial control can be taken care of with out the use of heavy antibiotics. Quorum sensing is therefore, an alternative method to control the production of biofilms and to reduce infections. With the identification of the compounds that act as signals and the production of quorum sensing blockers, it is now possible to make vaccines for this purpose.

Quorum sensing requires more research and investigation in order to become the therapy for the future. With the help of this technology, the dilemma of antibiotic resistance can finally be taken care of.

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Bacterial Diseases and Quorum Sensing
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