The role of chelators in preventing biofilm formation and catheter-related bloodstream infections
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The role of chelators in preventing biofilm formation and catheter-related bloodstream infectionsIssam I.Raad a,Xiang Fang a,Xavier M.Keutgen a,Ying Jiang a,Robert Sherertz b and Ray Hachem aIntroductionCentral venous catheters(CVCs)are an integral part of medical management infields such as oncology,nephrol-ogy and in the intensive care settings.Infections and thrombotic occlusion are the complications most com-monly associated with CVCs[1].One of every20CVCs inserted results in at least one bloodstream infection[2], which is associated in the critically ill patients with an estimated25%attributable mortality rate and an esti-mated cost in excess of$28000for each episode of catheter-related sepsis[3].The number of catheter-related bloodstream infection(CRBSI)is estimated to be more than400000cases annually[4].Following their attachment to the catheter surface, microorganisms,such as Staphylococcus aureus,Coagulase-negative Staphylococci and Candida species,undergo phenotypic and enzymatic changes resulting in the pro-duction of biofilm,an architecturally complex structure that is rich in exopolysaccharides and DNA[5–7,8 ,9–15]. Catheters within a short time after insertion become uniformly colonized with the microbial biofilm.The microorganisms then embed themselves in the biofilm layer and eventually become the sources of CRBSI and resistant to various antimicrobials[6,16–22]. Considering that intraluminal colonization is the major source of CRBSI in long-term CVC,the recent guidelines for prevention and treatment of CRBSI have proposed the use of intraluminal antimicrobial lock solutions,also known as antibiotic lock therapy(ALT),which is devel-oped to reduce the need of catheter removal,especially when long-term catheters are infected[23–25].ALT consists of instilling antimicrobial solutions at milligrama Department of Infectious Diseases,Infection Control and Employee Health,The University of Texas M.D. Anderson Cancer Center,Houston,Texas andb Section of Infectious Disease,Department of Internal Medicine,Bowman Gray School of Medicine,Wake Forest University,Winston-Salem,North Carolina,USA Correspondence to Issam I.Raad,MD,Department of Infectious Diseases,Infection Control and Employee Health,The University of Texas M.D.Anderson Cancer Center,1515Holcombe Boulevard,Unit402,Houston, TX77030,USATel:+17137927943;fax:+17137928233;e-mail:iraad@Current Opinion in Infectious Diseases2008, 21:385–392Purpose of reviewAs metallic cations are essential to microbial adherence,biofilm formation,and bacterial growth,efforts have been directed toward utilizing metal-binding chelators that have the capability of inhibiting bacterial growth by disrupting surface adherence and preventing biofilm production.This review focuses on recent advances in the role of chelators in biofilm disruption and prevention of catheter-related bloodstream infections.RecentfindingsThe most important factor in the pathogenesis of catheter-related bloodstream infections is the intraluminal colonization of the central venous catheters through the formation of bacterial biofilm matrix in which microbial organisms embed themselves and eventually become a source of catheter-related bloodstream infections.It has been demonstrated that high-affinity metal-binding chelators including ethylenediamine-tetraacetic acid and citrate have the capacity of inhibiting microbial growth by disrupting surface adherence and preventing biofilm production.Furthermore,ethylenediamine-tetraacetic acid and citrate have been clinically shown to be highly effective and outperform heparin in the prevention and treatment of catheter-related bloodstream infections when used as a component of antimicrobial catheter lock solutions. SummaryIt is suggested that the addition of chelators such as ethylenediamine-tetraacetic acid and citrate to antimicrobial lock solutions provides an innovative and superior alternative to heparin lock solution in the prevention and treatment of catheter-related bloodstream infections.Keywordsantimicrobial lock solution,biofilm,catheter-related bloodstream infection,chelator, metal ironCurr Opin Infect Dis21:385–392ß2008Wolters Kluwer Health|Lippincott Williams&Wilkins0951-73750951-7375ß2008Wolters Kluwer Health|Lippincott Williams&Wilkinsper milliliter(mg/ml)concentrations into the catheter lumen of an infected catheter and allowing the solutions to dwell for an extended period of time(8–10h per day) for the purpose of sterilizing the lumen[26–34].The antibiotic that is traditionally and commonly used in antimicrobial lock solutions is vancomycin at a concen-tration of100m g/ml–5mg/ml[23].However,vancomycin has limited activity against organisms in a biofilm [35,36,37 ].Several clinical studies have reported the failure of response or salvage using vancomycin contain-ing lock solutions[32,38–41].Metallic cations:enhancing microbial growth and adherenceMetallic cations have long been known to be essential to the cell growth and adherence of microbial pathogens (Table1)[42–50,51 ].Numbers of research have postu-lated a fact that Mg2þand Ca2þare involved in growth and differentiation of numerous bacterial strains[42,45,52–54].It has been shown that these divalent cations can stimulate cell-to-cell adhesion and thus promote aggrega-tion through the shared binding of divalent cations by cell wall teichoic acids thereby increasing the number of organisms adhering to afinite surface area[42,45,52–54].A recentfinding with regard to the role of calcium in regulating cell growth has revealed that the addition of Ca2þcauses at least a three-fold increase in alg gene expression during Pseudomonas aeruginosa growth in planktonic culture and as much as an eight-fold increase in alg expression during biofilm growth[43].In addition, Ca2þis an essential factor in the formation of thrombin and fibrin.Fibrinfilaments attach to the surface of indwelling catheters and serve as protein adhesins that promote the adherence of staphylococci to the surface of catheters that leads to CRBSI[55].Besides calcium and magnesium,iron is another key cation playing an important role in bacterial growth. Brubaker[47]indicated that all organisms require Fe3þfor growth and thus suggested that iron is an essential nutrient for the growth of most bacteria.Further research has demonstrated that the acquisition of iron is possibly the major determinant as to whether a microorganism is able to maintain itself within an animal host[48].Metallic cations and biofilm formationOne of the most important factors in the pathogenesis of CRBSI is the formation of adherent,multilayered bacterial biofilm matrix in which microbial organisms embed them-selves and eventually become a source of bloodstream infections emerging from CVCs[56].Most of the biofilm matrix is formed of an exopolysaccharide substance and DNA,produced by microbial organisms[8 ].Metal cations,such as magnesium,iron and calcium,play an important role in biofilm formation and maintenance (Table1).Two studies demonstrated that the metallic cations helped maintain biofilm structure by participating in the polymerization of bacterial exopolysaccharides [45,46].Another study on biofilm of P.aeruginosa also demonstrated that magnesium,calcium and iron func-tioned in stabilizing biofilm of bacteria[44].Specifically, magnesium was believed to be associated with the exopolysaccharide matrix,the primary part of most biofilm matrix.Furthermore,Sarkisova et al.[43]demonstrated in their research that the increased amount of alginate caused by the addition of Ca2þduring P.aeruginosa growth in planktonic culture resulted in biofilms that are as much as 20-fold thicker than those without added Ca2þthus suggesting that in biofilms,Ca2þmay play an important role in the observed increase in biofilm thickness by ionic cross-linking thereby modifying the biofilm architecture. In addition,the role of iron in biofilm formation has been investigated in several studies.Weinberg[49]indicated that biofilm development,a microbial cell differentiation, required a specific range of concentration of iron.Banin et al.[50]investigated the biofilm formation by a series of iron acquisition mutants of P.aeruginosa and demon-strated that intracellular iron serves as a signal in biofilm development.Recently,it was found that certain iron sources significantly increased the number of aggregates for rough strains thus suggesting that iron may contribute to the colonization and biofilm formation[51 ]. Disruption of biofilm and inhibition of bacterial growth by chelatorsAs metallic cations,such as iron,calcium and magnesium, are essential to microbial adherence,biofilm formation and bacterial growth,efforts have been directed toward386Nosocomial and healthcare related infectionsTable1The role of metals in cell growth,adherence and biofilm formationReferences cited in the text Metallic cation Function Organism[42–44]Calcium Involved in morphogenesis Candida albicans,Pseudomonas aeruginosaIncreases and stabilizesextracellular matrix of biofilm[44–46]Magnesium Increases adhesion Staphylococcus epidermidisIncreases slime production[44,47–50,51 ]Iron Serves as a signal in biofilmdevelopmentÁPseudomonas aeruginosa,Actinobacillus actinomycetemcomitansPromotes biofilm formationutilizing high-affinity metal-binding agents that can chelate these ions thereby inhibiting bacterial growth by disrupting surface adherence and preventing biofilm production(Fig.1,Table2)[57–68,69 ,70–80,81 ,82]. As shown in Fig.1,it has been hypothesized that the antimicrobial activity of cationic chelators stems from several mechanistic activities[83].First,metallic cations are necessary for prokaryotic cell division,and,second, they are important for the integrity of the bacterial cell wall.Ethylenediamine-tetraacetic acid(EDTA)and sodium citrate,on the contrary,are both capable of chelating metallic cations,such as calcium and magnes-ium,leading to inhibition of bacterial growth.Second, calcium chelators such as EDTA and citrate inhibit the fibrin formation of biofilm that is a necessary ingredient for the adherence of microbial organisms to the surface of an indwelling catheter.The third mechanism relates to the influence of chelators such as EDTA and sodium citrate on biofilm formation,and their use in treating biofilm-related infections has been reported by several research groups[44,46,57,58].The studies have shownThe role of chelators Raad et al.387Figure1The role of chelators in disrupting surface adherence,preventing biofilm formation and inhibiting bacterial growth Chalators play an important role in inhibitingbiofilm formation through their capabilities ofchelating metallic cations that are vital inbacterial cell growth and microbial adherencetofibrin and protein adherence.Table2In-vitro studies demonstrating the role of chelators in disruption of biofilm and inhibition of microbial growth References cited in the text Chelator Organism[44,57–68,69 ]EDTA Pseudomonas aeruginosa,Staphylococcus aureusStaphylococcus epidermidis,MRSA,Escherichia coliCandida albicans,Candida parapsilosis,Candida tropicalisCNS,Enterobacter,Enterococcus spp[60,65,67,70–74]Citrate Staphylococcus aureus,CNSStaphylococcus epidermidis,Pseudomonas aeruginosaEntercoccus faecalis,Candida albicans[75]Tf Staphylococcus epidermidis,Staphylococcus aureusPseudomonas aeruginosa[76]Lf Pseudomonas aeruginosa[77]EGTA Escherichia coli[78]Deferoxamine Staphylococcus aureus,Staphylococcus epidermidis,Escherichia coliProteus mirabilis[79]Bismuth dimercaprol Escherichia coli,Klebsiella pneumoniae,Enterobacter[64]DMSA Staphylococcus aureus coagulase[80]DTPA Branhamella catarrhalis,Candida pseudotropicalis[80]EHPG Staphylococcus epidermidis,Staphylococcus aureus,Pseudomonas aeruginosa,StaphylococcusbovisBranhamella catarrhalis,Yersinia,Micrococcus luteus[81 ]Deferasirox Rhizopus oryzae[82]Deferiprone Rhizopus oryzaeCNS,coagulase-negative staphylococci;DMSA,2,3-dimercaptosuccinic acid;DTPA,diethylene-triamine-pentaacetic acid;EDTA,ethylenediamine-tetraacetic acid;EGTA,ethylene glycol bis(beta-aminoethyl ether)-N,N,N0N0-tetraacetic acid;EHPG,N,N0-ethylenebis[2-(2-hydroxyphenyl)-glycine]; Lf,lactoferrin;Tf,transferrin.that these chelators have activity against biofilms of groups of microbial organisms including Staphylococci, P.aeruginosa and Candida.Hence,it has been demon-strated that EDTA and trisodium citrate(TSC)are useful in preventing the adherence of microbial organisms to catheter surfaces and are complementary or synergetic with various antibiotics in antimicrobial lock solutions used to prevent and treat CRBSI and thus increase the efficacy of such antibiotic lock solutions[59,60,70–73,84].Ethylenediamine-tetraacetic acidEDTA is a metal chelator with established anticoagulant activity and inhibitory activity against methicillin-resist-ant Staphylococci,Gram-negative bacilli and Candida species as well as other organisms[59,61–64].The activity of EDTA against biofilm cells is mediated by chelation of several divalent cations,such as calcium, magnesium and iron,that are required to stabilize the extracellular biofilm matrix[43,59,65–67].The EDTA chelation of these cations can enhance detachment of cells from the biofilm and in turn inhibit the biofilm formation[44].This dispersal process and the increased cell permeability facilitated by EDTA may also explain the enhanced killing observed in combining EDTA with antibiotics such as minocycline or gentamicin[44,59].It was reported that40mg/ml tetrasodium EDTA used in a lock solution for21h significantly reduced or potentially eradicated CVC-associated biofilm growth of clinically relevant microorganisms[58].Recently,EDTA,when used in combination with anti-biotics such as minocycline(M–EDTA)in a lock solution,has been shown both in vitro and in vivo to significantly reduce the density of colonization by S.epidermidis,S.aureus and C.albicans embedded in a biofilm[57,59].It was demonstrated in rabbits that the M–EDTA catheter lock solution was highly efficacious in preventing catheter-related colonization,bacteremia, septic phlebitis and endocarditis[59].In an in-vitro model,M–EDTA was significantly effective in reducing colonization of S.epidermidis,S.aureus and C.albicans [57].Given the fact that once organisms become embedded in the biofilm layer their resistance to anti-biotics increases,the combination of minocycline and EDTA is uniquely useful in disrupting the biofilm and in turn synergistically eradicating the organisms embedded in it[57,68].Trisodium citrateSeveral studies have demonstrated that TSC is synergis-tically effective in antimicrobial lock solutions[72,73]. Depending on the concentration used,15and30%TSC significantly reduced the number of colony-forming units (CFUs/ml)of S.aureus,S.epidermidis and Escherichia coli over a period of24h.Moreover,30%TSC also reduced the number of CFU/ml of C.albicans and P.aeruginosa.In addition to inhibiting bacterial growth,the researches also suggested that TSC,through its chelating activity on calcium and magnesium,could potentially disrupt the biofilm formation[65,72,73].To further investigate the minimum effective concen-tration of citrate against bacteria,Shanks et al.[67] have recently demonstrated that sodium citrate at con-centrations greater than0.5%efficiently inhibits biofilm formation and cell growth of S.aureus and S.epidermidis. They further showed that sodium citrate at2%concen-tration or greater powerfully inhibits in-vitro biofilm production by S.aureus and coagulase-negative staphy-lococci(CNS).Furthermore,a lower concentration of citrate(4%)was reported to be highly effective,when used in combination with taurolidine,in killing a diverse group of bacteria,including S.aureus,S.epidermidis, P.aeruginosa and Enterococcus faeclis,within biofilm [60].These results suggested that citrate-based catheter lock solution is promising for reducing the risk of biofilm-associated infections in indwelling catheter.In addition,citrate,like EDTA,was found to increase the permeability of the outer membrane of microorganisms thereby increasing their susceptibility to antimicrobial agents[74].Other chelatorsTransferrin(Tf)belongs to a family of iron-binding mono-meric glycoproteins and has been reported to possess a broad spectrum of antimicrobial properties attributed to its ability of chelating environmental iron thus making this essential nutrient inaccessible to an invading micro-organism[75].Lactoferrin(Lf),another iron-binding protein,has been shown by Singh et al.[76]to have the capacity of blocking biofilm development by P.aeruginosa. Several other chelators,including ethylene glycol bis(beta-aminoethyl ether)-N,N,N0N0-tetraacetic acid(EGTA), deferoxamine,bismuth dimercaprol,2,3-dimercaptosucci-nic acid(DMSA),diethylene-triamine-pentaacetic acid (DTPA),and N,N0-ethylenebis[2-(2-hydroxyphenyl)-glycine](EHPG),have also been demonstrated in vitro for their ability to disrupt biofilm formation and inhibit bacterial growth(Table2)[64,77–80].More recently, Ibrahim et al.[81 ,82]showed that iron chelators defer-iprone and deferasirox synergistically improved survival and decreased fungal burden when combined with lipo-somal amphotericin B.Chelators lock solutions and clinical studies There have been four clinical studies conducted to deter-mine the results of using M–EDTA as a lock solution in patients(Table3)[85–88].M–EDTA was utilized as a lock solution in indwelling ports inserted in14children388Nosocomial and healthcare related infectionswith cancer[86].The authors found that no port infections, thrombotic events or other adverse events were observed in the M–EDTA group,which was significant when compared with10port infections in heparin-flush group that consists of48control patients.While Raad et al.[88] discovered that M–EDTA was significantly efficacious at preventing recurrent CRBSI in three patients,Bleyer’s [85]team compared heparin with M–EDTA as aflush solution and suggested that M–EDTA had a better90-day catheter survival and significantly decreased the rate of catheter colonization.In addition,M–EDTA lock solution was shown to be effective in preventing catheter-related infections in patients receiving long-term parenteral nutrition[87].The group concluded that compared to standard heparinflush,M–EDTA lock solution signifi-cantly decreases the incidence of CRBSI in the high-risk long-term parenteral nutrition population.A randomized clinical trial comparing30%TSC to high-dose heparin used in lock solutions demonstrated that TSC significantly reduced catheter-related infections and the number of major bleeding episodes associated with these lock solutions(Table3)[73].Moreover, taurolidine and4%citrate as a catheter lock solution has been demonstrated to dramatically reduce the frequency of catheter-related bacteremia(Table3) [70,71].Recently,a randomized controlled study compar-ing gentamicin and3.13%citrate to heparin alone as a lock solution in the prevention of catheter-related infec-tions discovered that the infection-free duration of catheter use was significantly higher in the gentamicin and citrate group than in the heparin group(Table3)[89]. Thus,it has been concluded that gentamicin–citrate lock solution appears to be a highly effective strategy for the reduction of morbidity,and potential mortality and costs, associated with catheter-related infections.Ethanol in antibiotics–chelator lock solution Although the combination of antibiotics with chelators is synergistically active in eradicating organisms embedded in biofilm on catheter surfaces,they(like all other anti-biotic catheter locks)require a prolonged dwell time of at least16–24h in order to demonstrate significant activity against a high inoculum of organisms embedded in biofilm[59,69 ].This prolonged dwell time might not be feasible or achievable in most clinical situations. Ethanol,on the contrary,has been shown to have broad-spectrum antimicrobial activity against microbial organisms embedded in biofilm after a dwell time of only 1–2h.While the use of high concentrations of ethanol may be associated with side effects[90],lower and safer concentration of50%ethanol alone has limited activity against staphylococcal organisms embedded in biofilm as tested in an animal model[91].However,ethanol activity can be significantly enhanced when combined with anti-biotics and chelators in lock solutions.It was recently demonstrated that a triple combination of3mg/ml of minocycline and30mg/ml of EDTA(M–EDTA)in 25%ethanol used as a catheter lock solution is rapidly and synergistically active in eradicating staphylococcal and Candida organisms embedded in biofilm,within a dwell time ranging from15to60min[69 ].Further studies by Chandra et al.[92,93]have shown that a triple combination of trimethoprim(TMP),EDTA and ethanol is superior to any of these components alone in prevention and treatment of bacterial and fungal biofilms. The authors tested the combination against C.albicans, methicillin-resistant S.aureus(MRSA)and P.aeruginosa biofilms and demonstrated that it was able to prevent biofilm formation even after short-term exposure (15min)and eradicated mature phase biofilm afterThe role of chelators Raad et al.389Table3Clinical studies evaluating lock solutions containing chelators against catheter-related infections Referencescited in the text Catheterlock solution Type of catheter/populationNo.of CRBSI or no.ofcolonization/no.of ptsor cathetersCRBSI rate(no.ofCRBSI per1000catheter-days)P-valueCatheter locksolution groupControlgroupCatheter locksolution groupControlgroup[85]M–EDTA Hemodialysis catheter1/119/14NA NA0.01a[86]M–EDTA Infusion ports in pediatric cancer patients0/1410/480 2.20.05[87]M–EDTA Long-term parental nutrition population1/747/70.79.50.0001b[88]M–EDTA Groshong catheter/nontunneled silicone CVC0/340/3c017.3<0.01b [71]Taurolidine–citrate Hemodialysis catheter(tunneled and untunneled)0/374/390 2.10.047 [70]Taurolidine–citrate Hemodialysis catheter(long-term,tunneled)1/2016/300.6 5.6<0.001 [89]Gentamicin–citrate Hemodialysis catheter(tunneled)0/537/550.3 4.20.002 [73]TSC Hemodialysis catheter(tunneled and untunneled)9/14833/143 1.1 4.1<0.001 CNS,coagulase-negative staphylococci;CRBSI,catheter-related bloodstream infection;CVCs,central venous catheters;EDTA,ethylenediamine-tetraacetic acid;M–EDTA,minocycline–EDTA;NA,no such information in the study;TSC,trisodium citrate.a P-value was from a test comparing colonization rate between the two groups.b P-value was from a test comparing CRBSI rate per1000catheter-days between the two groups.All other P-values were from CRBSI-free survival analysis(log-rank test)in each study.c In this study,each patient used himself as his control.Control group are the patients when without using catheter lock solution,and solution group are patients when using catheter lock solution.long-term exposure(2–4h).On the basis of these studies, the triple combination of an antibiotic,a chelator and a low concentration of ethanol(25%)provides an optimal antimicrobial catheter lock solution that is rapidly active within a short time(within2h)[89,92,93].Chelators as alternative to heparinToday’s standard of care for maintaining catheter patency is heparin or isotonic saline lock solutions.Although the use of heparin in an antibiotic lock solution is compatible and well tolerated,it has not been proven to enhance or complement antimicrobials in preventing or treating CVC-related infections[94].Thisfinding might be related in part to the fact that heparin alone does not have any antimicrobial activity[95].Furthermore,the use of heparin in lock solutions is associated with some risk factors,such as heparin-induced thrombocytopenia and thrombosis[96].Moreover,several investigators recently reported that heparin enhances the formation of S.aureus biofilm on catheter surfaces[67,91]possibly mediated by S.aureus’ability of producing a heparin-binding protein[59,91,97,98].Therefore,as heparin alternatives, chelators such as EDTA and citrate have significant advantages including providing three necessary and important functions:an anticoagulant effect,an anti-biofilm effect,and a synergistic antimicrobial effect, enhancing the antimicrobial activity of the antibiotic or antiseptic used.ConclusionInfection is a significant limitation to the use of implan-table intravascular devices,such as indwelling catheters, especially over extended period of time.The initial event in the development of biomaterial-centered infection is the adhesion of bacteria to the implant surface,leading to colonization of the substratum and subsequent biofilm production[75].Therefore,disruption of the initial step of bacterial adhesion to the biomaterial surface, which may lead otherwise to intravascular catheter-related infections,such as CRBSI,may provide enormous benefits for patients with implanted vascular devices.On the contrary,metallic cations,such as Ca2þ,Fe3þand Mg2þ,play a regulatory role in bacterial growth and biofilm formation by mostly promoting and enhancing such processes.Hence,chelators that have the capacity of interfering with bacterial cation metabolism,such as Ca2þ,Fe3þand Mg2þ,did prove to be extremely valuable for the prevention and treatment of CRBSI and other intravascular device-related infections.Chelating agents, such as EDTA,TSC,Tf,and Lf,have been demon-strated to have antibiofilm activity and antibacterial effect,which may improve the quality of antimicrobial lock solutions and in turn help prevent CRBSI and eradicate established infections.Further investigations through in-vitro and clinical studies are either in progress or needed in the future to improve the current applications as well as explore new potential of these chelators in the management of CRBSI,including determining the most effective and safest concentrations of EDTA and TSC and the addition of other components, such as antimicrobials with ethanol,in catheter lock solutions in order to effectively prevent CRBSI. References and recommended readingPapers of particular interest,published within the annual period of review,have been highlighted as:of special interestof outstanding interestAdditional references related to this topic can also be found in the Current World Literature section in this issue(pp.451–452).1Raad I,Luna M,Khalil S,et al.The relationship between the thrombotic and infectious complications of central venous catheters.JAMA1994;271:1014–1016.2Maki D,Cobb L,Garman J,et al.An attachable silver-impregnated cuff for prevention of infection with central venous catheters:a prospective rando-mized multicenter trial.Am J Med1988;85:307–314.3Pittet D,Tarara D,Wenzel R.Nosocomial bloodstream infection in critically ill patients:excess length of stay,extra costs,and attributable mortality.JAMA 1994;271:1598–1601.4Raad I.Intravascular-catheter-related ncet1998;351:893–898.5Tojo M,Yamashita N,Goldmann DA,et al.Isolation and characterization of a capsular polysaccharide adhesion from Staphylococcus epidermidis.J Infect Dis1988;157:713–722.6Sheth N,Franson T,Sohnle P.Influence of bacterial adherence to intravas-cular catheters on in-vitro antibiotic ncet1985;2:1266–1268.7Falcieri E,Vaudaux P,Huggler E,et al.Role of bacterial exopolymers and host factors on adherence and phagocytosis of Staphylococcus aureus in foreign body infection.J Infect Dis1987;155:524–531.8Qin Z,Ou Y,Yang L,et al.Role of autolysin-mediated DNA release in biofilm formation of Staphylococcus epidermidis.Microbiology2007;153:2083–2092.This study suggested that extracellular DNA promotes biofilm formation of S.epidermidis.9Christensen G,Simpson W,Bisno A,et al.Adherence of slime producing strains of Staphylococcus epidermidis to smooth surfaces.Infect Immun 1982;37:318–326.10Christensen G,Simpson W,Younger J,et al.Adherence of coagulase-negative staphylococci to plastic tissue culture plates:a quantitative model for the adherence of staphylococci to medical devices.J Clin Microbiol1985;22:996–1006.11Montanaro L,Arciola C,Borsetti E,et al.A polymerase chain reaction(PCR) method for the identification of collagen adhesion gene(CNA)in Staphy-lococcus-induced prosthesis infections.New Microbiol1998;21:359–363.12McKenney D,Pouliot K,Wang Y,et al.Broadly protective vaccine for Staphylococcus aureus based on an in vitro-expressed antigen.Science 1999;284:1523–1527.13Cramton S,Gerko C,Schnell N,et al.The intercellular adhesion(ica)hocus is present in Staphylococcus aureus and is required for biofilm formation.Infect Immun1999;67:5427–5433.14Arciola C,Montanaro L,Baldassarri L,et al.Slime production by staphylo-cocci isolated from prosthesis-associated infections.New Microbiol1999;22:337–341.15Ammendolia M,Di Rosa R,Montanaro L,et al.Slime production and expres-sion of the slime associated antigen by staphylococcal clinical isolated.J Clin Microbiol1999;37:3235–3238.16Stewart P,Costerton J.Antibiotic resistance of bacteria in biofincet 2001;358:135–138.17Pfaller M,Messer S,Hollis R.Variations in DNA subtype,antifungal suscept-ibility,and slime production among clinical isolates of Candida parapsilosis.Diagn Microbiol Infect Dis1995;21:9–14.390Nosocomial and healthcare related infections。