Published on June 21, 2011
POPULAR SCIENCE SUMMARY ON ‘Slimy business - The Biotechnology of Biofilms’NAME: ISHMAM NAWARID: 081510047FACULTY: SDL
Slimy business - The Biotechnology of BiofilmsBacteria are more anthropoid in nature than we thought they were, at least from a sociologist’spoint of view. Just like we tend to end up clinging in a community rather than settle for ahermetic life, these little microbes are being discovered to do the same thing too. In fact, not onlydo they stick together in what the scientists call a “biofilm”, they have put on a notorious edge totheir communal way of life as well!What are Biofilms?On a more stricter definition, biofilms are the highly structured living arrangements of bacteria (or other microbes) that forms the slime layer we so often see forming on medical implants andother hydrated surfaces. An analogy can be made between the biofilm and a city because withinthe biofilm there is division of labor and mutual living (i.e. bacteria live off each others waste-products and productions.) They attach to each other and to the solid support by excreting asubstance called EPS (extracellular polymeric substance) that forms a sticky matrix. Often, thereare more than one species colonizing one biofilm. For example, the yellowish layer on our teethcalled dental plaque carries over 400 different bacterial species. As gross as it might sound, theselittle folks have developed fantastic ways to make sure we do not harm their existence or brushthem out of our teeth! Microscope view of dental plaque.Microscope view of a biofilm in the nozzle of a The plaque consists of overdentist’s instrument used to clear away drilling 400 different species of bacteria.debris in a patient’s mouth.
The composition of the slimy layer differs depending on the species of organism involved. Gramnegative bacteria makes neutral or polyanionic biofilms whereas Gram positive bacteria producecationic ones. Other adjuvants might effect the stability of the layer, for example metal ions cancause better cross-linking and hence, stickier and stabler matrix of polyanionic EPS. On the otherhand, lactoferrin, an iron binding protein in mammals prevents P.aeruginosa from formingbiofilms.Such convivial conglomerates of microbes do more than just stick to surfaces. In fact, theycommunicate with each other through chemical signaling. When enough of the chemical hasaccumulated, it means that there is enough microbes to commence the formation of biofilm. Themicrobes then start changing their lifestyles to suit living in a community than living separately.The process of chemically sensing the population density is called Quorum sensing. Quorumsensing forms the basis for many anti-biofilm drug designers as disrupting Quorum sensing caninhibit communication and thus, biofilm formation.Fig. 1: The biofilm life cycle. 1: individual cells populate the surface. 2: extracellular polymericsubstance (EPS) is produced and attachment becomes irreversible. 3 & 4: cells become layeredand effects of quorum sensing begins. 5: cluster reaches maximum thickness and single cells arereleased from the biofilmThe biofilm problemThe proverb “Unity is Strength” probably never had such a negative connotation as it does whiledescribing biofilms. United, the microbes in the biofilm defend against their killers (antibiotics):they employ mechanisms to destroy antibiotics, build up impenetrable bastion so that themicrobes’ demons can’t reach them.Once in biofilm, bacteria can be several folds more resistant to antibiotics than when they livefreely. This could be due to one of the following reasons:
1. Most antibiotics kill rapidly dividing cells. This works for normal bacterias because they have a very fast rate of reproduction ( e.g. they double every 20 minutes). However, in biofilms, bacteria replicate much more slowly. So the antibiotic might not be effective here. 2. The thick sticky matrix is difficult for the drug to penetrate. 3. Some bacteria adapts and changes their outward appearance to protect themselves from the action of antibiotics 4. In the biofilm are regions where nutrients and waste products of the community collect. If antibiotic reaches that part, it might be destroyed. 5. The bacteria might change from inside genetically. Certain genes are switched on that makes them insensitive against the antibiotic.Whatever the reason, antibiotic resistance of biofilms are a huge concern for people in themedical and research arena. Biofilms on catheters, pacemakers, artificial joints can lead to deadlyinfections. In fact, The National Institute of Health estimated that biofilms cause over 80% ofinfections. According to the Biomedical Market Newsletter, catheter related bloodstreaminfections solely can cause increased mortality, longer stays in hospitals and increased medicalcost ( around $6000 more per patient). Most of the circulatory and urinary tract infections thatwe see are probably due to devices inserted inside our body that harbors biofilms.Scientists are still to catch up on the varied aspects of biofilms. This is mostly because so far,research was focused more on the free- living microbes rather than on the community.Researchers typically use single-celled (planktonic) microbes as experimental models becausethey are easy to study and manipulate. Too preoccupied with the “lonely” mode of bacteriallifestyle, scientists have either overlooked or ended up with devastating consequences wherethey mistook planktonic bacteria to be similar to biofilmic ones. After heart valve replacementoperations, many patients developed infection and eventually died out of a condition calledendocarditis. St. Jude Medical, a medical device company, developed a silver coating to preventformation of biofilms. However, it was seen that patients with silver coated device had moreinfection than patients with uncoated device. This huge disaster occurred simply because themanufacturers used stuff that would kill free living bacteria rather than those in biofilms.P.aeruginosa is the most thoroughly studied bacteria because it is the most common cause ofhospital acquired infection. S.epidermis is the species that causes long and short term infections
associated with transdermal devices ( devices that need to penetrate the skin). Fungal biofilmsare also being studied recently.Investing in BiofilmsAs bacteria enjoy their shelter within biofilms, our scientists are certainly not going to sit aroundwatching them make happy families within pace makers. With increasing knowledge onbacterias’ communal way of life, many biotechnology companies have evolved to research anddevelop biofilm related products. The following are some of the companies that are researchingon biofilms and their main approach in short: ● Quorum Sciences: They screen for chemicals that inhibits quorum sensing or biofilm formation ● Quorex: AI-2 is a chemical that communicates between microbes. If communication can be inhibited, biofilm formation can be disrupted. Quorex is trying to develop inhibitors of AI-2 ● Microbia: In a biofilm, certain genes of microbes are more actively expressed. Therefore, these genes must have some connection in developing resistance. Microbia developes chemicals that works against these genes. Also, they try to sensitize bacteria against antibiotics. ● Antex: They screen compounds for prevention and disruption of biofilmsSome natural products have been seen to inhibit biofilm formation. Delsea pulchra is a red algaefound in Australia’s Botany Bay. These algae synthesizes organic compounds called furanoneswith chlorine or bromine attached that wards off bacterial biofilms. ● Biosignals: They have identified 200 structures similar to the halogenated furanone and are evaluating each as a potent biofilm disrupter. The mechanism of action of these furanone analogs is that they interfere with AHL action ( AHL is a signal in bacteria that causes them to aggregate together and glow. Biofilm formation also requires AHL signaling). Compounds inhibiting AI-2 dependent quorum sensing have also been identified. ● Sequoia: They screen plant materials in search of biofilm inhibitors and disruptors.
Bioremediation – biofilms to the rescueBy now, the word biofilm probably has become synonymous with “ slimy terrors” and it is trulyso. Its resilient nature toward antibiotic and its infective nature is the cause of headaches ofmany. However, biofilm can have its share of usefulness too.Bioremediation is the process of cleaning up wastes with the use of biological entities. The verynature of bacteria “ clinging” together in a biofilm can be of immense help in bioremediation.For example if an area is contaminated with excess fertilizer, biofilms are encouraged to formunderground by adding nutrients. The biofilm forms a “biobarrier” that restricts the flow ofcontaminated water through that region and also destroys excess nitrogen in the water. Similarstrategy can also be used to enhance oil recovery. Oilfields no longer in use can be “plugged” offby encouraging biofilm growth and hence water can be redirected to regions that have untappedoil. Using sulfate-reducing bacteria in a biofilm, the biofilm can be used for mine remediation.The bacteria will “eat” up the metals in the contaminated water and precipitate metal sulfides.Therefore, from a different angle, biofilms can serve as our “community of laborers”. They canbe made to work for cleaning up crude oil, jet fuel, environmental pollutants, etc.Conclusion/ CritiqueIn this era, where we are already facing a crisis of effective antimicrobial agents, comes anothernew dimension to this problem: Biofilms.The slimy layer, that forms on many hydrated surface,pose significant threat to human health due to its resistance to antibiotics. Thus, it is of nowonder that a big share of hospital acquired infections are attributed to these biofilms. Moredeadly are the biofilms that grows on surfaces of pacemakers and other implants. Research ofbiofilm structure has revealed the formation of a matrix whose composition varies from speciesto species. Various chemical signals are used for inter and intra microbial communications. Ofprime importance is the Quorum sensing mechanism that utilizes signals such as AI-2 and AHL.It is only recently that biotechnology firms have started to acknowledge the problems ofbiofilms. They are trying out different strategies to discover novel antibiotics that are effectiveagainst the biofilms. Strategies include prevention of biofilm formation, develope drugs to treatexisting biofilms or try and disrupt the polymeric ties that bind the biofilms together.Many firmsthat deal with biofilms aim mostly at quorum sensing mechanisms to inhibit biofilm growth orformation. Natural inhibitors of biofilms have also been discovered like the halogenatedfuranones of red algae.
From algal metabolite to Pseudomonas drug. (A) Compound 2, a natural furanone compound isolatedfrom (C) D.pulchra. (B) compound C-30, a synthetic furanone with enhanced Quorum Sensing Inhibitionactivity.However, before conclusive research, it is very important to make a good model for testingantibiofilm drugs. Biofilms are certainly more dynamic than scientists so far have discovered.The volume of data that accumulates each day makes it difficult to settle for an appropriatemodel. For example, P.aeruginosa that was always known to be a aerobic microbe turned out tobe anaerobic in biofilms in the lungs of cystic fibrosis patients. According to Roberto Kolter, toassume that surface associated bacteria grown in synthetic medium in a flow cell in vivo arephysiologically similar to surface associated bacteria growing on any specific site within the hostis rather funny and irresponsible. Therefore, proper models and right parameters is the key tovalid results. If a product is formulated, it should be applied to actual biofilms in actualenvironment. Rather than jumping on to formulating drugs, they should converge in discoveringthe biofilm’s nature in more details first. In no way should a species that exist in biofilm bethought to be similar to its planktonic counterpart. Or else, we will again see the repetition of theheart-valve disaster.
Abb. 2: Makromoleküle eines Biofilms. (Modifiziert nach Fuchs) Von oben: Cytoplasma (CP) eines sphaeroplastierten Bakteriums mit Cytoplasmamembran (CPM).
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