Microbial biofilms: biosurfactants as antibiofilm agents

Applied Microbiology and Biotechnology

Volumn 98, Issue 24, 2014, Pages 9915-9929

  Banat, Ibrahim M ^a   De Rienzo, Mayri A Díaz ^b   Quinn, Gerry A ^c  

^a UNIVERSITY OF ULSTER   (United Kingdom)

^b UNIVERSITY OF MANCHESTER   (United Kingdom)

^c SWANSEA UNIVERSITY   (United Kingdom)

Author keywords

Adjuvants; Antibiofilm; Antimicrobial; Biofilm; Biosurfactants; Dispersal agents; Disruption

Indexed keywords

ANTIMICROBIAL AGENTS; BIOMOLECULES; SURFACE ACTIVE AGENTS;

ADJUVANTS; ANTI-BIOFILM; ANTIMICROBIAL; BIO-SURFACTANTS; DISRUPTION;

BIOFILMS;

BIOFILM; EMERGENCE; GROWTH RATE; HOSPITAL SECTOR; MICROBIAL ACTIVITY; SURFACTANT; YEAST;

BACTERIA (MICROORGANISMS);

ANTIINFECTIVE AGENT; SURFACTANT;

BACTERIAL PHENOMENA AND FUNCTIONS; BACTERIUM; BIOFILM; DRUG EFFECTS; FUNGUS; GROWTH, DEVELOPMENT AND AGING; METABOLISM; PHYSIOLOGY;

ANTI-INFECTIVE AGENTS; BACTERIA; BACTERIAL PHYSIOLOGICAL PHENOMENA; BIOFILMS; FUNGI; SURFACE-ACTIVE AGENTS;

EID: 84916608726     PISSN: 01757598     EISSN: 14320614     Source Type: Journal    
DOI: 10.1007/s00253-014-6169-6     Document Type: Review

References (102)

1. Abdel-Mawgoud AM, Lepine F, Deziel E (2010) Rhamnolipids: diversity of structures, microbial origins and roles. Appl Microbiol Biotechnol 86:1323–1336
2. Alhede M, Qvortrup K, Liebrechts R, Hoiby N, Givskov M, Bjarnsholt T (2012) Combination of microscopic techniques reveals a comprehensive visual impression of biofilm structure and composition. FEMS Immunol Med Microbiol 65:335–342
3. Araujo JC, Téran FC, Oliveira RA, Nour EA, Montenegro MA, Campos JR, Vazoller RF (2003) Comparison of hexamethyldisilazane and critical point drying treatments for SEM analysis of anaerobic biofilms and granular sludge. J Electron Microsc (Tokyo) 52:429–433
4. Arnold TM, Forrest GN, Messmer KJ (2007) Polymyxin antibiotics for gram-negative infections. Am J Health-Syst Pharm 64:819–826
5. Banat IM, Makkar RS, Cameotra SS (2000) Potential commercial applications of microbial surfactants. Appl Microbiol Biotechnol 53:495–508
6. Banat IM, Franzetti A, Gandolfi I, Bestetti G, Martinotti MG, Fracchia L, Smyth TJ, Marchant R (2010) Microbial biosurfactants production, applications and future potential. Appl Microbiol Biotechnol 87:427–444
7. Benincasa M, Abalos A, Oliveira I, Manresa A (2004) Chemical structure, surface properties and biological activities of the biosurfactant produced by Pseudomonas aeruginosa LBI from soapstock. Anton Leeuw 85:1–8
8. Benoit MR, Conant CG, Lonescu-Zanetti C, Schwartz M, Martin A (2010) New device for high-throughput viability screening of flow biofilms. App Environ Microbiol 76:4136–4142
9. Bevins CL, Zasloff M (1990) Peptides from frog skin. Annu Rev Biochem 59:395–414
10. Boles BR, Thoendel M, Singh PK (2005) Rhamnolipids mediate detachment of Pseudomonas aeruginosa from biofilms. Mol Microbiol 57:1210–1223
11. Brasseur R, Braun N, El Kirat K, Deleu M, Mingeot-Leclercq MP, Dufrene YF (2007) The biologically important surfactin lipopeptide induces nanoripples in supported lipid bilayers. Langmuir 23:9769–9772
12. Bueno J (2014) Anti-biofilm drug susceptibility testing methods: looking for new strategies against resistance mechanism. J Microbial Biochem Technol S3:004. doi:10.4172/1948-5948.S3-004
13. Ceri H, Olson ME, Stremick C, Read RR, Morck D, Buret A (1999) The Calgary biofilm device: new technology for rapid determination of antibiotic susceptibilities of bacterial biofilms. J Clin Microbiol 37:1771–1776
14. Chabane NY, Mlouka MB, Alexandre S, Nicol M, Marti S, Pestel-Caron M, Vila J, Dé Jouenne T (2014) Virstatin inhibits biofilm formation and motility of Acinetobacter baumannii. BMC Microbiol 14:62
15. Cochis A, Fracchia L, Martinotti MG, Rimondini L (2012) Biosurfactants prevent in vitro Candida albicans biofilm formation on resins and silicon materials for prosthetic devices. Oral Surg Oral Med Oral Pathol Oral Radiol 113:755–761
16. Costa SG, Deziel E, Lepine F (2011) Characterization of rhamnolipid production by Burkholderia glumae. Lett Appl Microbiol 53:620–627
17. Croda-García G, Grosso-Becerra V, Gonzalez-Valdez A, Servín-González L, Soberón-Chávez G (2011) Transcriptional regulation of Pseudomonas aeruginosa rhlR: role of the CRP orthologue Vfr (virulence factor regulator) and quorum-sensing regulators LasR and RhlR. Microbiology 157:2545–2555
18. D'Auria L, Deleu M, Dufour S, Mingeot-Leclercq MP, Tyteca D (2013) Surfactins modulate the lateral organization of fluorescent membrane polar lipids: a new tool to study drug: membrane interaction and assessment of the role of cholesterol and drug acyl chain length. Biochim Biophys Acta 1828:2064–2073
19. Davey ME, Caiazza NC, O'Toole GA (2003) Rhamnolipid surfactant production affects biofilm architecture in Pseudomonas aeruginosa PAO1. J Bacteriol 185:1027–1036
20. Davies D (2003) Understanding biofilm resistance to antibacterial agents. Nat Rev Drug Discov 2:114–122
21. Decho AW (2013) The EPS matrix as an adaptive bastion for biofilms: introduction to special issue. Int J Mol Sci 14:23297–23300
22. Deng Y, Lu Z, Bi H, Lu F, Zhang C, Bie X (2011) Isolation and characterization of peptide antibiotics LI-F04 and polymyxin B6 produced by Paenibacillus polymyxa strain JSa-9. Peptides 32:1917–1923
23. Desai JD, Banat IM (1997) Microbial production of surfactants and their commercial potential. Microbiol Mol Biol Rev 61:47–64
24. Ding Y, Wang W, Fan M, Tong Z, Kuang R, Jiang W, Ni L (2014) Antimicrobial and anti-biofilm effect of Bac8c on major bacteria associated with dental caries and Streptococcus mutans biofilms. Peptides 52:61–67
25. Domingues MM, Inacio RG, Raimundo JM, Martins M, Castanho MA, Santos NC (2012) Biophysical characterization of polymyxin B interaction with LPS aggregates and membrane model systems. Biopolymers 98:338–344
26. Doring G, Conway SP, Heijerman HGM, Hodson ME, Hoiby N, Smyth A, Touw DJ (2000) Antibiotic therapy against Pseudomonas aeruginosa in cystic fibrosis: a European consensus. Eur Respir J 16:749–767
27. Dowd SE, Wolcott RD, Sun Y, McKeehan T, Smith E, Rhoads D (2008) Polymicrobial nature of chronic diabetic foot ulcer biofilm infections determined using bacterial Tag encoded FLX amplicon pyrosequencing (bTEFAP). PLoS One 3:e3326
28. Dubern JF, Lugtenberg BJ, Bloemberg GV (2006) The ppuI-rsaL-ppuR quorum-sensing system regulates biofilm formation of Pseudomonas putida PCL1445 by controlling biosynthesis of the cyclic lipopeptides putisolvins I and II. J Bacteriol 188:2898–2906
29. Dusane DH, Nancharaiah YV, Zinjarde SS, Venugopalan VP (2010) Rhamnolipid mediated disruption of marine Bacillus pumilus biofilms. Colloids Surf B Biointerfaces 81:242–248
30. Dusane DH, Pawar VS, Nancharaiah YV, Venugopalan VP, Kumar AR, Zinjarde SS (2011) Anti-biofilm potential of a glycolipid surfactant produced by a tropical marine strain of Serratia marcescens. Biofouling 27:645–654
31. Dusane DH, Dam S, Nancharaiah YV, Kumar AR, Venugopalan VP, Zinjarde SS (2012) Disruption of Yarrowia lipolytica biofilms by rhamnolipid biosurfactant. Aquat Biosyst 8:17
32. Epstein AK, Pokroy B, Seminara A, Aizenberg J (2011) Bacterial biofilm shows persistent resistance to liquid wetting and gas penetration. Proc Natl Acad Sci U S A 108:995–1000
33. Falagas ME, Kasiakou SK (2005) Colistin: the revival of polymyxins for the management of multidrug-resistant gram-negative bacterial infections. Clin Infect Dis 40:1333–1341
34. Falagas ME, Kasiakou SK (2006) Toxicity of polymyxins: a systematic review of the evidence from old and recent studies. Crit Care 10:R27
35. Fracchia L, Cavallo M, Martinotti MG, Banat IM (2012) Biosurfactants and Bioemulsifiers Biomedical and Related Applications – Present Status and Future Potentials. In: Biomedical Science, Engineering and Technology. pp 325-370
36. Gakhar L, Bartlett JA, Penterman J, Mizrachi D, Singh PK, Mallampalli RK, Ramaswamy S, McCray PB (2010) PLUNC is a novel airway surfactant protein with anti-biofilm activity. PLoS One 5:e9098
37. Ganz T, Selsted ME, Szklarek D, Harwig SS, Daher K, Bainton DF, Lehrer RI (1985) Defensins Natural peptide antibiotics of human neutrophils. J Clin Invest 76:1427–1435
38. Girard LP, Ceri H, Gibb AP, Olson M, Sepandj F (2010) MIC versus MBEC to determine the antibiotic sensitivity of Staphylococcus aureus in peritoneal dialysis peritonitis. Perit Dial Int 30:652–656
39. Gudina EJ, Rocha V, Teixeira JA, Rodrigues LR (2010) Antimicrobial and antiadhesive properties of a biosurfactant isolated from Lactobacillus paracasei ssp. paracasei A20. Lett Appl Microbiol 50:419–424
40. Haba E, Pinazo A, Jauregui O, Espuny MJ, Infante MR, Manresa A (2003) Physicochemical characterization and antimicrobial properties of rhamnolipids produced by Pseudomonas aeruginosa 47 T2 NCBIM 40044. Biotechnol Bioeng 81:316–322
41. He J, Ledesma KR, Lam WY, Figueroa DA, Lim TP, Chow DS, Tam VH (2010) Variability of polymyxin B major components in commercial formulations. Int J Antimicrob Agents 35:308–310
42. Irie Y, O'Toole GA, Yuk MH (2005) Pseudomonas aeruginosa rhamnolipids disperse Bordetella bronchiseptica biofilms. FEMS Microbiol Lett 250:237–243
43. Janek T, Lukaszewicz M, Rezanka T, Krasowska A (2010) Isolation and characterization of two new lipopeptide biosurfactants produced by Pseudomonas fluorescens BD5 isolated from water from the Arctic Archipelago of Svalbard. Bioresour Technol 101:6118–6123
44. Janek T, Lukaszewicz M, Krasowska A (2012) Antiadhesive activity of the biosurfactant pseudofactin II secreted by the Arctic bacterium Pseudomonas fluorescens BD5. BMC Microbiol 12:24
45. Jass J, Lappin-Scott HM (1996) The efficacy of antibiotics enhanced by electrical currents against Pseudomonas aeruginosa biofilms. J Antimicrob Chemother 38:987–1000
46. Joshi-Navare K, Prabhune A (2013) A biosurfactant sophorolipid acts in synergy with antibiotics to enhance their efficiency BioMed Res Int; 1-8
47. Kim KM, Lee JY, Kim CK, Kang JS (2009) Isolation and characterization of surfactin produced by Bacillus polyfermenticus KJS-2. Arch Pharm Res 32:711–715
48. Kiran GS, Sabarathnam B, Selvin J (2010) Biofilm disruption potential of a glycolipid biosurfactant from marine Brevibacterium casei. FEMS Immunol Med Microbiol 59:432–438
49. Kotulova D, Slobodnikova L (2010) Susceptibility of staphylococcus aureus biofilms to vancomycin, gentamicin and rifampin. Epidemiol Mikrobiol Imunol 59:80–87
50. Krasowska A (2010) Biomedical activity of biosurfactants. Postepy Hig Med Dosw 64:310-313
51. Krupovic M, Daugelavicius R, Bamford DH (2007) Polymyxin B induces lysis of marine Pseudoalteromonads Antimicrob Agents. Chemotherapy 51:3908–3914
52. Kuiper I, Lagendijk EL, Pickford R, Derrick JP, Lamers GEM, Thomas-Oates JE, Lugtenberg BJJ, Bloemberg GV (2004) Characterization of two Pseudomonas putida lipopeptide biosurfactants, putisolvin I and II, which inhibit biofilm formation and break down existing biofilms. Mol Microbiol 51:97–113
53. Lehtinen J, Nuutila J, Lilius EM (2004) Green fluorescent protein-propidium iodide (GFP-PI) based assay for flow cytometric measurement of bacterial viability. Cytometry 60A:165–172
54. Leis AP, Schlicher S, Franke H, Strathmann M (2005) Optically transparent porous medium for nondestructive studies of microbial biofilm architecture and transport dynamics. Appl Environ Microbiol 71:4801–4808
55. Liu L, Tan X, Jia A (2012) Relationship between bacterial quorum sensing and biofilm formation–a review. Acta Microbiol Sin 52:271–278
56. Lourenco A, Machado H, Brito L (2011) Biofilms of Listeria monocytogenes produced at 12 degrees C either in pure culture or in co-culture with Pseudomonas aeruginosa showed reduced susceptibility to sanitizers. J Food Sci 76:M143–M148
57. Lourenco A, Coenye T, Goeres DM, Donelli G, Azevedo AS, Ceri H, Coelho FL, Flemming HC, Juhna T, Lopes SP, Oliveira R, Oliver A, Shirtliff ME, Sousa AM, Stoodley P, Pereira MO, Azevedo NF (2014) Minimum information about a biofilm experiment (MIABiE): standards for reporting experiments and data on sessile microbial communities living at interfaces. Pathogens Dis 70:250–256
58. Luna JM, Rufino RD, Sarubbo LA, Rodrigues LR, Teixeira JA, de Campos-Takaki GM (2011) Evaluation antimicrobial and antiadhesive properties of the biosurfactant Lunasan produced by Candida sphaerica UCP 0995. Curr Microbiol 62:1527–1534
59. Mandal SM (2012) A novel hydroxyproline rich glycopeptide from pericarp of Datura stramonium: proficiently eradicate the biofilm of antifungals resistant Candida albicans. Biopolymers 98:332–337
60. Marchant R, Banat IM (2012a) Biosurfactants: a sustainable replacement for chemical surfactants? Biotechnol Lett 34:1597–1605
61. Marchant R, Banat IM (2012b) Microbial biosurfactants: challenges and opportunities for future exploitation. Trends Biotechnol 30:558–565
62. McLaughlin RA, Hoogewerf AJ (2006) Interleukin-1beta-induced growth enhancement of Staphylococcus aureus occurs in biofilm but not planktonic cultures. Microb Pathog 41:67–79
63. Milletli Sezgin F, Coban AY, Gunaydin M (2012) Investigation of biofilm formation in Acinetobacter baumannii isolates and their colistin susceptibilities in biofilm. Int J Antimicrob Agents 41:199
64. Mireles JR 2nd, Toguchi A, Harshey RM (2001) Salmonella enterica serovar typhimurium swarming mutants with altered biofilm-forming abilities: surfactin inhibits biofilm formation. J Bacteriol 183:5848–5854
65. Mukherji R, Prabhune A (2014) Novel glycolipids synthesized using plant essential oils and their application in quorum sensing inhibition and as antibiofilm agents. Sci World J 2014:890709
66. Muthusamy K, Gopalakrishnan S, Ravi TK, Sivachidambaram P (2008) Biosurfactants: Properties, commercial production and application. Curr Sci 94:736–747
67. Neu TR (1996) Significance of bacterial surface-active compounds in interaction of bacteria with interfaces. Microbiol Rev 60:151–166
68. Olson ME, Ceri H, Morck DW, Buret AG, Read RR (2002) Biofilm bacteria: formation and comparative susceptibility to antibiotics. Can J Vet Res 66:86–92
69. O'Toole GA (2011) Microtiter dish biofilm formation assay. J Vis Exp Jan 30(47):2437. doi:10.3791/2437
70. Pamp SJ, Tolker-Nielsen T (2007) Multiple roles of biosurfactants in structural biofilm development by Pseudomonas aeruginosa. J Bacteriol 189:2531–2539
71. Pecci Y, Rivardo F, Martinotti MG, Allegrone G (2010) LC/ESI-MS/MS characterisation of lipopeptide biosurfactants produced by the Bacillus licheniformis V9T14 strain. J Mass Spectrom 45:772–778
72. Pereira MO, Machado I, Simões M, Vieira MJ (2007) Preventing biofilm formation using surfactants. BiofilmClub©. 167-74. http://hdl.handle.net/1822/7534 accessed May 2014
73. Pradhan AK, Pradhan N, Mall G, Panda HT, Sukla LB, Panda PK, Mishra BK (2013) Application of lipopeptide biosurfactant isolated from a halophile: Bacillus tequilensis CH for inhibition of biofilm. Appl Biochem Biotechnol 171:1362–1375
74. Price NP, Rooney AP, Swezey JL, Perry E, Cohan FM (2007) Mass spectrometric analysis of lipopeptides from Bacillus strains isolated from diverse geographical locations. FEMS Microbiol Lett 271:83–89
75. Quinn GA, Maloy AP, McClean S, Carney B, Slater JW (2012) Lipopeptide biosurfactants from Paenibacillus polymyxa inhibit single and mixed species biofilms. Biofouling 28:1151–1166
76. Raza W, Yang X, Wu H, Wang Y, Xu Y, Shen Q (2009) Isolation and characterisation of fusaricidin-type compound-producing strain of Paenibacillus polymyxa SQR-21 active against Fusarium oxysporum f.sp.nevium. Eur J Plant Pathol 125:471–483
77. Read RC, Roberts P, Munro N, Rutman A, Hastie A, Shryock T, Hall R, McDonald-Gibson W, Lund V, Taylor G (1992) Effect of Pseudomonas aeruginosa rhamnolipids on mucociliary transport and ciliary beating. J Appl Physiol 72:2271–2277
78. Rivardo F, Turner RJ, Allegrone G, Ceri H, Martinotti MG (2009) Anti-adhesion activity of two biosurfactants produced by Bacillus spp. prevents biofilm formation of human bacterial pathogens. Appl Microbiol Biotechnol 83:541–553
79. Rivardo F, Martinotti MG, Turner RJ, Ceri H (2011) Synergistic effect of lipopeptide biosurfactant with antibiotics against Escherichia coli CFT073 biofilm. Int J Antimicrob Agents 37:324–331
80. Rodrigues L, van der Mei HC, Teixeira J, Oliveira R (2004) Influence of biosurfactants from probiotic bacteria on formation of biofilms on voice prostheses. Appl Environ Microbiol 70:4408–4410
81. Rodrigues L, Banat IM, Teixeira J, Oliveira R (2006a) Biosurfactants: potential applications in medicine. J Antimicrob Chemother 57:609–618
82. Rodrigues L, Banat IM, van der Mei HC, Teixeira JA, Oliveira R (2006b) Interference in adhesion of bacteria and yeasts isolated from explanted voice prostheses to silicone rubber by rhamnolipid biosurfactants. J Appl Microbiol 100:470–480
83. Rodrigues L, van der Mei HC, Banat IM, Teixeira J, Oliveira R (2006c) Inhibition of microbial adhesion to silicone rubber treated with biosurfactant from Streptococcus thermophilus A. FEMS Immunol Med Microbiol 46:107–112
84. Rodrigues L, Banat IM, Teixeira J, Oliveira R (2007) Strategies for the prevention of microbial biofilm formation on silicone rubber voice prostheses. J Biomed Mater Res Part B- Appl Biomater 81B:358–370
85. Rollet C, Gal L, Guzzo J (2009) Biofilm-detached cells, a transition from a sessile to a planktonic phenotype: a comparative study of adhesion and physiological characteristics in Pseudomonas aeruginosa. FEMS Microbiol Lett 290:135–142
86. Rufino RD, Luna JM, Sarubbo LA, Rodrigues LR, Teixeira JA, Campos-Takaki GM (2011) Antimicrobial and anti-adhesive potential of a biosurfactant Rufisan produced by Candida lipolytica UCP 0988. Colloids Surf B Biointerfaces 84:1–5
87. Samadi N, Abadian N, Ahmadkhaniha R, Amini F, Dalili D, Rastkari N, Safaripour E, Mohseni FA (2012) Structural characterization and surface activities of biogenic rhamnolipid surfactants from Pseudomonas aeruginosa isolate MN1 and synergistic effects against methicillin-resistant Staphylococcus aureus. Folia Microbiol 57:501–508
88. Satpute SK, Banpurkar AG, Dhakephalkar PK, Banat IM, Chopade BA (2009) Methods for investigating biosurfactants and bioemulsifiers: A review. Crit Rev Biotechnol 30:127–144
89. Sepandj F, Ceri H, Gibb A, Read R, Olson M (2004) Minimum inhibitory concentration (MIC) versus minimum biofilm eliminating concentration (MBEC) in evaluation of antibiotic sensitivity of gram-negative bacilli causing peritonitis. Perit Dial Int 24:65–67
90. Sriram MI, Kalishwaralal K, Deepak V, Gracerosepat R, Srisakthi K, Gurunathan S (2011) Biofilm inhibition and antimicrobial action of lipopeptide biosurfactant produced by heavy metal tolerant strain Bacillus cereus NK1. Colloids Surf B Biointerfaces 85:174–181
91. Stepanovic S, Cirkovic I, Ranin L, Svabic-Vlahovic M (2004) Biofilm formation by Salmonella spp. and Listeria monocytogenes on plastic surface. Lett Appl Microbiol 38:428–432
92. Stepanovic S, Vukovic D, Hola V, Di Bonaventura G, Djukic S, Cirkovic I, Ruzicka F (2007) Quantification of biofilm in microtiter plates: overview of testing conditions and practical recommendations for assessment of biofilm production by staphylococci. APMIS 115:891–899
93. Stewart CR, Muthye V, Cianciotto NP (2012) Legionella pneumophila Persists within Biofilms Formed by Klebsiella pneumoniae, Flavobacterium sp., and Pseudomonas fluorescens under Dynamic Flow Conditions. PLoS One 7:e50560
94. Stoodley P, Sauer K, Davies DG, Costerton JW (2002) Biofilms as complex differentiated communities. Annu Rev Microbiol 56:187–209
95. Tahmourespour A, Salehi R, Kasra Kermanshahi R (2011) Lactobacillus acidophilus-Derived Biosurfactant Effect on GTFB and GTFC Expression Level in Streptococcus mutans Biofilm Cells. Braz J Microbiol 42:330–339
96. Velraeds MMC, van de Belt-Gritter B, Busscher HJ, Reid G, van der Mei HC (2000) Inhibition of uropathogenic biofilm growth on silicone rubber in human urine by lactobacilli - a teleologic approach. World J Urol 18:422–426
97. Villa F, Cappitelli F (2013) Plant-derived bioactive compounds at sub-lethal concentrations: towards smart biocide-free antibiofilm strategies. Phytochem Rev 12:245–254
98. Wicken AJ, Knox KW (1980) Bacterial cell surface amphiphiles. Biochim Biophys Acta 604:1–26
99. Wu ZY, Ye CS, Guo F, Zhang SH, Yu X (2013) Evidence for Broad-Spectrum Biofilm Inhibition by the Bacterium Bacillus sp Strain SW9. Appl Environ Microbiol 79:1735–1738
100. Xu Z, Shao J, Li B, Yan X, Shen Q, Zhang R (2013) Contribution of Bacillomycin D in Bacillus amyloliquefaciens SQR9 to Antifungal Activity and Biofilm Formation. Appl Environ Microbiol 79:808–815
101. Zakaria Gomaa E (2013) Antimicrobial and anti-adhesive properties of biosurfactant produced by lactobacilli isolates, biofilm formation and aggregation ability. J Gen Appl Microbiol 59:425-–36
102. Zhang Y (2014) Persisters, persistent infections and the Yin-Yang model. Emerg Microbes Infect 3: e3. Published online: doi:10.1038/emi.2014.3