Abstract
Legionella pneumophila (L. pneumophila) is the causative agent of Legionnaires’ disease. Transmission to humans is mediated via inhalation of contaminated water droplets. L. pneumophila is widely distributed in man-made water systems, multiple species of protozoa, and nematodes. L. pneumophila persist within multi-species biofilms that cover surfaces within water systems. Virulence, spread, and resistance to biocides are associated with survival of L. pneumophila within multi-organismal biofilm. Outbreaks of Legionellosis are correlated with the existence of L. pneumophila in biofilms, even after the intensive chemical and physical treatments. Several factors negatively or positively modulate the persistence of L. pneumophila within the microbial consortium-containing L. pneumophila. Biofilm-forming L. pneumophila continue to be a public health and economic burden and directly influence the medical and industrial sectors. Diagnosis and hospitalization of patients and prevention protocols cost governments billions of dollars. Dissecting the biological and environmental factors that promote the persistence and physiological adaptation in biofilms can be fundamental to eliminating and preventing the transmission of L. pneumophila. Herein, we review different factors that promote persistence of L. pneumophila within the biofilm consortium, survival strategies used by the bacteria within biofilm community, gene regulation, and finally challenges associated with biofilm resistance to biocides and anti-Legionella treatments.
Keywords
- legionella pneumophila
- biofilm
- Legionellosis
- protozoa
- Caenorhabditis elegans
1. Introduction
Multiple mechanisms of persistence are harbored by
Herein, we review factors that mediate biofilm persistence, strategies utilized by the bacteria to become a member of the biofilm consortium and modes of eradicating
1.1 Constituents of L. pneumophila biofilm
Biofilm formation of
Our knowledge is lacking regarding the factors encoded by
1.2 Formation of biofilms as a survival niche in oligotrophic environment
Biofilm is extremely nutritious environment that harbors a mixture of living, dead organisms as well as protozoa and bacteria. To be a productive member of the microbial consortium,
Obtaining the required carbon, nitrogen, and amino acids for replication of
The second mechanism by which
1.3 Factors influencing biofilm formation by L. pneumophila
1.3.1 Cyclic-di-GMP
Regulation of bacterial pathogenesis and biofilm formation has been associated with the bacterial second messenger Cyclic-dimeric diguanylate (c-di-GMP) [59–62]. Biofilm regulation for several bacteria has been shown to be reliant on c-di-GMP [63–65]. Two main enzymes have been implicated in regulating the synthesis of the c-di-GMP. (I) A diguanylate cyclases (DGCs) containing GGDEF domain mediates the production of c-di-GMP from two GTPs molecules [66]. (II) A phosphodiesterases (PDEs) proteins containing EAL domain that mediate the degradation of c-di-GMP [66].
The
The Haem Nitric oxide/Oxygen (H-NOX) binding domains family of hemoprotein sensors have been demonstrated to play a role in regulating biofilm formation and the c-di-GMP activity [70]. Intriguingly,
1.3.2 Iron
Even though it is essential for
1.3.3 Genetic control
Even though biofilm formation plays a role in the colonization, survival, dissemination and likely the pathogenesis of
Binding to sulfated glycosaminoglycans (CAGs) of the host extracellular matrix is mediated via the
1.3.4 Quorum sensing
In Gram-negative bacteria, gene expression of several bacterial processes, including virulence, sporulation, bioluminescence, competence and biofilm formation is regulated by quorum sensing (QS) [85, 86]. Quorum sensing bacteria are usually identified in man-made water systems and it is well appreciated that QS signaling regulate environmental biofilm production [87]. The LAI-1 (3-hydroxypentadecane-4-one) QS autoinducer is the only (
1.4 Modulation of gene expression in biofilms
Differential gene expression between planktonic and biofilm forming
Further, examining the expression of the macrophage infectivity potentiator (
1.5 Biocides treatments of L. pneumophila biofilm and bacterial resistance
Other methods have been used to limit
2. Conclusions
Several chemical and physical parameters can influence the behavior of
Acknowledgments
Studies in Dr. Amer’s laboratory are supported by The Ohio State University Center for Clinical and Translational Science Longitudinal Pilot Award (CCTS), R21 AI113477, R01 AI24121 and R01 HL127651. Studies in Dr. Abu Khweek’s laboratory are supported by Birzeit University.
Conflict of interest
The authors of the manuscript declare that the submitted work was carried out in the absence of any personal, professional or financial relationships that could potentially be construed as a conflict of interest.
Author contributions
Arwa Abu Khweek wrote the book chapter, and Amal O. Amer edited the manuscript.
References
- 1.
Fraser DW et al. Legionnaires’ disease: Description of an epidemic of pneumonia. The New England Journal of Medicine. 1977; 297 (22):1189-1197 - 2.
Wagner C et al. Collagen binding protein Mip enables legionella pneumophila to transmigrate through a barrier of NCI-H292 lung epithelial cells and extracellular matrix. Cellular Microbiology. 2007; 9 (2):450-462 - 3.
Steinert M, Hentschel U, Hacker J. Legionella pneumophila: an aquatic microbe goes astray. FEMS Microbiology Reviews. 2002; 26 (2):149-162 - 4.
Fields BS, Benson RF, Besser RE. Legionella and Legionnaires’ disease: 25 years of investigation. Clinical Microbiology Reviews. 2002; 15 (3):506-526 - 5.
Isberg RR, O’Connor TJ, Heidtman M. The legionella pneumophila replication vacuole: Making a cosy niche inside host cells. Nature Reviews. Microbiology. 2009; 7 (1):13-24 - 6.
de Felipe KS et al. Evidence for acquisition of legionella type IV secretion substrates via interdomain horizontal gene transfer. Journal of Bacteriology. 2005; 187 (22):7716-7726 - 7.
Abu Khweek A et al. The Sphingosine-1-phosphate Lyase (LegS2) contributes to the restriction of legionella pneumophila in murine macrophages. PLoS One. 2016; 11 (1):e0146410 - 8.
Khweek AA et al. A bacterial protein promotes the recognition of the legionella pneumophila vacuole by autophagy. European Journal of Immunology. 2013; 43 (5):1333-1344 - 9.
Losick VP, Isberg RR. NF-kappaB translocation prevents host cell death after low-dose challenge by legionella pneumophila. The Journal of Experimental Medicine. 2006; 203 (9):2177-2189 - 10.
de Felipe KS et al. Legionella eukaryotic-like type IV substrates interfere with organelle trafficking. PLoS Pathogens. 2008; 4 (8):e1000117 - 11.
Price CT et al. Host proteasomal degradation generates amino acids essential for intracellular bacterial growth. Science. 2011; 334 (6062):1553-1557 - 12.
Belyi Y et al. Legionella pneumophila glucosyltransferase inhibits host elongation factor 1A. Proceedings of the National Academy of Sciences of the United States of America. 2006; 103 (45):16953-16958 - 13.
Laguna RK et al. A legionella pneumophila-translocated substrate that is required for growth within macrophages and protection from host cell death. Proceedings of the National Academy of Sciences of the United States of America. 2006; 103 (49):18745-18750 - 14.
Newton HJ et al. Molecular pathogenesis of infections caused by legionella pneumophila. Clinical Microbiology Reviews. 2010; 23 (2):274-298 - 15.
O’Toole G, Kaplan HB, Kolter R. Biofilm formation as microbial development. Annual Review of Microbiology. 2000; 54 :49-79 - 16.
Andreozzi E et al. Role of biofilm in protection of the replicative form of legionella pneumophila. Current Microbiology. 2014; 69 (6):769-774 - 17.
Hindre T et al. Transcriptional profiling of legionella pneumophila biofilm cells and the influence of iron on biofilm formation. Microbiology. 2008; 154 (Pt 1):30-41 - 18.
Mampel J et al. Planktonic replication is essential for biofilm formation by legionella pneumophila in a complex medium under static and dynamic flow conditions. Applied and Environmental Microbiology. 2006; 72 (4):2885-2895 - 19.
Stewart CR, Muthye V, Cianciotto NP. Legionella pneumophila persists within biofilms formed by Klebsiella pneumoniae, Flavobacterium sp., and Pseudomonas fluorescens under dynamic flow conditions. PLoS One. 2012; 7 (11):e50560 - 20.
Atlas RM. Legionella: From environmental habitats to disease pathology, detection and control. Environmental Microbiology. 1999; 1 (4):283-293 - 21.
Berk SG et al. Packaging of live legionella pneumophila into pellets expelled by Tetrahymena spp. does not require bacterial replication and depends on a dot/Icm-mediated survival mechanism. Applied and Environmental Microbiology. 2008; 74 (7):2187-2199 - 22.
Faulkner G, Garduno RA. Ultrastructural analysis of differentiation in legionella pneumophila. Journal of Bacteriology. 2002; 184 (24):7025-7041 - 23.
Steinert M et al. Resuscitation of viable but nonculturable legionella pneumophila Philadelphia JR32 by Acanthamoeba castellanii. Applied and Environmental Microbiology. 1997; 63 (5):2047-2053 - 24.
Garcia MT et al. Acanthamoeba polyphaga resuscitates viable non-culturable legionella pneumophila after disinfection. Environmental Microbiology. 2007; 9 (5):1267-1277 - 25.
Valster RM, Wullings BA, van der Kooij D. Detection of protozoan hosts for legionella pneumophila in engineered water systems by using a biofilm batch test. Applied and Environmental Microbiology. 2010; 76 (21):7144-7153 - 26.
Horwitz MA. Formation of a novel phagosome by the Legionnaires’ disease bacterium (legionella pneumophila) in human monocytes. The Journal of Experimental Medicine. 1983; 158 (4):1319-1331 - 27.
Declerck P et al. Replication of legionella pneumophila in biofilms of water distribution pipes. Microbiological Research. 2009; 164 (6):593-603 - 28.
Declerck P. Biofilms: The environmental playground of legionella pneumophila. Environmental Microbiology. 2010; 12 (3):557-566 - 29.
Shirtliff ME, Mader JT, Camper AK. Molecular interactions in biofilms. Chemistry & Biology. 2002; 9 (8):859-871 - 30.
Sutherland IW. The biofilm matrix--an immobilized but dynamic microbial environment. Trends in Microbiology. 2001; 9 (5):222-227 - 31.
Costerton JW. Overview of microbial biofilms. Journal of Industrial Microbiology. 1995; 15 (3):137-140 - 32.
Costerton JW et al. Bacterial biofilms in nature and disease. Annual Review of Microbiology. 1987; 41 :435-464 - 33.
Pecastaings S et al. Sessile legionella pneumophila is able to grow on surfaces and generate structured monospecies biofilms. Biofouling. 2010; 26 (7):809-819 - 34.
Piao Z et al. Temperature-regulated formation of mycelial mat-like biofilms by legionella pneumophila. Applied and Environmental Microbiology. 2006; 72 (2):1613-1622 - 35.
Taylor M, Ross K, Bentham R. Legionella, protozoa, and biofilms: Interactions within complex microbial systems. Microbial Ecology. 2009; 58 (3):538-547 - 36.
Vervaeren H et al. Introduction of a boost of legionella pneumophila into a stagnant-water model by heat treatment. FEMS Microbiology Ecology. 2006; 58 (3):583-592 - 37.
Wu MC et al. Isolation of genes involved in biofilm formation of a Klebsiella pneumoniae strain causing pyogenic liver abscess. PLoS One. 2011; 6 (8):e23500 - 38.
Basson A, Flemming LA, Chenia HY. Evaluation of adherence, hydrophobicity, aggregation, and biofilm development of Flavobacterium johnsoniae-like isolates. Microbial Ecology. 2008; 55 (1):1-14 - 39.
Kives J, Orgaz B, Sanjose C. Polysaccharide differences between planktonic and biofilm-associated EPS from Pseudomonas fluorescens B52. Colloids and Surfaces. B, Biointerfaces. 2006; 52 (2):123-127 - 40.
Guerrieri E et al. Effect of bacterial interference on biofilm development by legionella pneumophila. Current Microbiology. 2008; 57 (6):532-536 - 41.
Mallegol J et al. Essential roles and regulation of the legionella pneumophila collagen-like adhesin during biofilm formation. PLoS One. 2012; 7 (9):e46462 - 42.
Watnick P, Kolter R. Biofilm, city of microbes. Journal of Bacteriology. 2000; 182 (10):2675-2679 - 43.
George JR et al. Amino acid requirements of legionella pneumophila. Journal of Clinical Microbiology. 1980; 11 (3):286-291 - 44.
Edelstein PH. Comparative study of selective media for isolation of legionella pneumophila from potable water. Journal of Clinical Microbiology. 1982; 16 (4):697-699 - 45.
Wadowsky RM, Yee RB. Satellite growth of legionella pneumophila with an environmental isolate of Flavobacterium breve. Applied and Environmental Microbiology. 1983; 46 (6):1447-1449 - 46.
Tison DL et al. Growth of legionella pneumophila in association with blue-green algae (cyanobacteria). Applied and Environmental Microbiology. 1980; 39 (2):456-459 - 47.
Rowbotham TJ. Preliminary report on the pathogenicity of legionella pneumophila for freshwater and soil amoebae. Journal of Clinical Pathology. 1980; 33 (12):1179-1183 - 48.
Newsome AL et al. Isolation of an amoeba naturally harboring a distinctive legionella species. Applied and Environmental Microbiology. 1998; 64 (5):1688-1693 - 49.
Loret JF, Greub G. Free-living amoebae: Biological by-passes in water treatment. International Journal of Hygiene and Environmental Health. 2010; 213 (3):167-175 - 50.
Murga R et al. Role of biofilms in the survival of legionella pneumophila in a model potable-water system. Microbiology. 2001; 147 (Pt 11):3121-3126 - 51.
Rowbotham TJ. Pontiac fever, amoebae, and legionellae. Lancet. 1981; 1 (8210):40-41 - 52.
Hagele S et al. Dictyostelium discoideum: A new host model system for intracellular pathogens of the genus legionella. Cellular Microbiology. 2000; 2 (2):165-171 - 53.
Kikuhara H et al. Intracellular multiplication of legionella pneumophila in Tetrahymena thermophila. Journal of UOEH. 1994; 16 (4):263-275 - 54.
Bigot R et al. Intra-amoeba multiplication induces chemotaxis and biofilm colonization and formation for legionella. PLoS One. 2013; 8 (10):e77875 - 55.
Temmerman R et al. Necrotrophic growth of legionella pneumophila. Applied and Environmental Microbiology. 2006; 72 (6):4323-4328 - 56.
Brassinga AK et al. Caenorhabditis is a metazoan host for legionella. Cellular Microbiology. 2010; 12 (3):343-361 - 57.
Hellinga JR et al. Identification of vacuoles containing extraintestinal differentiated forms of legionella pneumophila in colonized Caenorhabditis elegans soil nematodes. Microbiology. 2015; 4 (4):660-681 - 58.
Rasch J et al. Legionella-protozoa-nematode interactions in aquatic biofilms and influence of Mip on Caenorhabditis elegans colonization. International Journal of Medical Microbiology. 2016; 306 (6):443-451 - 59.
Tamayo R, Pratt JT, Camilli A. Roles of cyclic diguanylate in the regulation of bacterial pathogenesis. Annual Review of Microbiology. 2007; 61 :131-148 - 60.
Romling U, Galperin MY, Gomelsky M. Cyclic di-GMP: The first 25 years of a universal bacterial second messenger. Microbiology and Molecular Biology Reviews. 2013; 77 (1):1-52 - 61.
Martinez-Gil M, Ramos C. Role of cyclic di-GMP in the bacterial virulence and evasion of the plant immunity. Current Issues in Molecular Biology. 2017; 25 :199-222 - 62.
Abu Khweek A, Fetherston JD, Perry RD. Analysis of HmsH and its role in plague biofilm formation. Microbiology. 2010; 156 (Pt 5):1424-1438 - 63.
Conner JG et al. The ins and outs of cyclic di-GMP signaling in vibrio cholerae. Current Opinion in Microbiology. 2017; 36 :20-29 - 64.
Valentini M, Filloux A. Biofilms and cyclic di-GMP (c-di-GMP) Signaling: Lessons from Pseudomonas aeruginosa and other bacteria. The Journal of Biological Chemistry. 2016; 291 (24):12547-12555 - 65.
Bobrov AG et al. Systematic analysis of cyclic di-GMP signalling enzymes and their role in biofilm formation and virulence in Yersinia pestis. Molecular Microbiology. 2011; 79 (2):533-551 - 66.
Simm R et al. GGDEF and EAL domains inversely regulate cyclic di-GMP levels and transition from sessility to motility. Molecular Microbiology. 2004; 53 (4):1123-1134 - 67.
Pecastaings S et al. New insights into legionella pneumophila biofilm regulation by c-di-GMP signaling. Biofouling. 2016; 32 (8):935-948 - 68.
Levi A et al. Cyclic diguanylate signaling proteins control intracellular growth of legionella pneumophila. MBio. 2011; 2 (1):e00316-e00310 - 69.
Allombert J et al. Three antagonistic cyclic di-GMP-catabolizing enzymes promote differential dot/Icm effector delivery and intracellular survival at the early steps of legionella pneumophila infection. Infection and Immunity. 2014; 82 (3):1222-1233 - 70.
Carlson HK, Vance RE, Marletta MA. H-NOX regulation of c-di-GMP metabolism and biofilm formation in legionella pneumophila. Molecular Microbiology. 2010; 77 (4):930-942 - 71.
Radtke AL, O’Riordan MX. Intracellular innate resistance to bacterial pathogens. Cellular Microbiology. 2006; 8 (11):1720-1729 - 72.
Reeves MW et al. Metal requirements of legionella pneumophila. Journal of Clinical Microbiology. 1981; 13 (4):688-695 - 73.
Schaible UE, Kaufmann SH. Iron and microbial infection. Nature Reviews. Microbiology. 2004; 2 (12):946-953 - 74.
Andrews SC, Robinson AK, Rodriguez-Quinones F. Bacterial iron homeostasis. FEMS Microbiology Reviews. 2003; 27 (2-3):215-237 - 75.
Lemire JA, Harrison JJ, Turner RJ. Antimicrobial activity of metals: Mechanisms, molecular targets and applications. Nature Reviews. Microbiology. 2013; 11 (6):371-384 - 76.
Musk DJ, Banko DA, Hergenrother PJ. Iron salts perturb biofilm formation and disrupt existing biofilms of pseudomonas aeruginosa. Chemistry & Biology. 2005; 12 (7):789-796 - 77.
Portier E et al. Iron availability modulates the persistence of legionella pneumophila in complex biofilms. Microbes and Environments. 2016; 31 (4):387-394 - 78.
Lau HY, Ashbolt NJ. The role of biofilms and protozoa in legionella pathogenesis: Implications for drinking water. Journal of Applied Microbiology. 2009; 107 (2):368-378 - 79.
De Buck E et al. Legionella pneumophila Philadelphia-1 tatB and tatC affect intracellular replication and biofilm formation. Biochemical and Biophysical Research Communications. 2005; 331 (4):1413-1420 - 80.
Heuner K et al. Influence of the alternative sigma(28) factor on virulence and flagellum expression of legionella pneumophila. Infection and Immunity. 2002; 70 (3):1604-1608 - 81.
Molofsky AB, Shetron-Rama LM, Swanson MS. Components of the legionella pneumophila flagellar regulon contribute to multiple virulence traits, including lysosome avoidance and macrophage death. Infection and Immunity. 2005; 73 (9):5720-5734 - 82.
Abu Khweek A et al. Biofilm-derived legionella pneumophila evades the innate immune response in macrophages. Frontiers in Cellular and Infection Microbiology. 2013; 3 :18 - 83.
Schell U, Simon S, Hilbi H. Inflammasome recognition and regulation of the legionella flagellum. Current Topics in Microbiology and Immunology. 2016; 397 :161-181 - 84.
Duncan C et al. Lcl of legionella pneumophila is an immunogenic GAG binding adhesin that promotes interactions with lung epithelial cells and plays a crucial role in biofilm formation. Infection and Immunity. 2011; 79 (6):2168-2181 - 85.
Zhu J et al. Quorum-sensing regulators control virulence gene expression in vibrio cholerae. Proceedings of the National Academy of Sciences of the United States of America. 2002; 99 (5):3129-3134 - 86.
Ng WL, Bassler BL. Bacterial quorum-sensing network architectures. Annual Review of Genetics. 2009; 43 :197-222 - 87.
Shrout JD, Nerenberg R. Monitoring bacterial twitter: Does quorum sensing determine the behavior of water and wastewater treatment biofilms? Environmental Science & Technology. 2012; 46 (4):1995-2005 - 88.
Tiaden A et al. The legionella pneumophila response regulator LqsR promotes host cell interactions as an element of the virulence regulatory network controlled by RpoS and LetA. Cellular Microbiology. 2007; 9 (12):2903-2920 - 89.
Tiaden A et al. Synergistic contribution of the legionella pneumophila lqs genes to pathogen-host interactions. Journal of Bacteriology. 2008; 190 (22):7532-7547 - 90.
Spirig T et al. The legionella autoinducer synthase LqsA produces an alpha-hydroxyketone signaling molecule. The Journal of Biological Chemistry. 2008; 283 (26):18113-18123 - 91.
Tiaden A et al. The autoinducer synthase LqsA and putative sensor kinase LqsS regulate phagocyte interactions, extracellular filaments and a genomic island of legionella pneumophila. Environmental Microbiology. 2010; 12 (5):1243-1259 - 92.
Miller MB et al. Parallel quorum sensing systems converge to regulate virulence in vibrio cholerae. Cell. 2002; 110 (3):303-314 - 93.
Kimura S et al. Pseudomonas aeruginosa las quorum sensing autoinducer suppresses growth and biofilm production in legionella species. Microbiology. 2009; 155 (Pt 6):1934-1939 - 94.
Bruggemann H et al. Virulence strategies for infecting phagocytes deduced from the in vivo transcriptional program of legionella pneumophila. Cellular Microbiology. 2006; 8 (8):1228-1240 - 95.
Rocha ER, Smith CJ. Role of the alkyl hydroperoxide reductase (ahpCF) gene in oxidative stress defense of the obligate anaerobe bacteroides fragilis. Journal of Bacteriology. 1999; 181 (18):5701-5710 - 96.
LeBlanc JJ, Davidson RJ, Hoffman PS. Compensatory functions of two alkyl hydroperoxide reductases in the oxidative defense system of legionella pneumophila. Journal of Bacteriology. 2006; 188 (17):6235-6244 - 97.
Cianciotto NP, Fields BS. Legionella pneumophila mip gene potentiates intracellular infection of protozoa and human macrophages. Proceedings of the National Academy of Sciences of the United States of America. 1992; 89 (11):5188-5191 - 98.
Wieland H et al. Intracellular multiplication of legionella pneumophila depends on host cell amino acid transporter SLC1A5. Molecular Microbiology. 2005; 55 (5):1528-1537 - 99.
Blasco MD, Esteve C, Alcaide E. Multiresistant waterborne pathogens isolated from water reservoirs and cooling systems. Journal of Applied Microbiology. 2008; 105 (2):469-475 - 100.
Buse HY et al. Microbial diversities (16S and 18S rRNA gene pyrosequencing) and environmental pathogens within drinking water biofilms grown on the common premise plumbing materials unplasticized polyvinylchloride and copper. FEMS Microbiology Ecology. 2014; 88 (2):280-295 - 101.
Kim BR et al. Literature review--efficacy of various disinfectants against legionella in water systems. Water Research. 2002; 36 (18):4433-4444 - 102.
Borella P et al. Water ecology of legionella and protozoan: Environmental and public health perspectives. Biotechnology Annual Review. 2005; 11 :355-380 - 103.
Giao MS et al. Incorporation of natural uncultivable legionella pneumophila into potable water biofilms provides a protective niche against chlorination stress. Biofouling. 2009; 25 (4):335-341 - 104.
Cooper IR, Hanlon GW. Resistance of legionella pneumophila serotype 1 biofilms to chlorine-based disinfection. The Journal of Hospital Infection. 2010; 74 (2):152-159 - 105.
Hilbi H, Hoffmann C, Harrison CF. Legionella spp. outdoors: Colonization, communication and persistence. Environmental Microbiology Reports. 2011; 3 (3):286-296 - 106.
Steinert M et al. Regrowth of legionella pneumophila in a heat-disinfected plumbing system. Zentralbl Bakteriol. 1998; 288 (3):331-342 - 107.
Dupuy M et al. Efficiency of water disinfectants against legionella pneumophila and Acanthamoeba. Water Research. 2011; 45 (3):1087-1094 - 108.
Berk SG et al. Production of respirable vesicles containing live legionella pneumophila cells by two Acanthamoeba spp. Applied and Environmental Microbiology. 1998; 64 (1):279-286 - 109.
Bouyer S et al. Long-term survival of legionella pneumophila associated with Acanthamoeba castellanii vesicles. Environmental Microbiology. 2007; 9 (5):1341-1344 - 110.
Storey MV et al. The efficacy of heat and chlorine treatment against thermotolerant Acanthamoebae and legionellae. Scandinavian Journal of Infectious Diseases. 2004; 36 (9):656-662 - 111.
Farhat M et al. Effects of disinfection on legionella spp., eukarya, and biofilms in a hot water system. Applied and Environmental Microbiology. 2012; 78 (19):6850-6858 - 112.
Schwartz T, Hoffmann S, Obst U. Formation of natural biofilms during chlorine dioxide and u.v. disinfection in a public drinking water distribution system. Journal of Applied Microbiology. 2003; 95 (3):591-601 - 113.
Hijnen WA, Beerendonk EF, Medema GJ. Inactivation credit of UV radiation for viruses, bacteria and protozoan (oo)cysts in water: A review. Water Research. 2006; 40 (1):3-22 - 114.
Pang CM, Liu WT. Biological filtration limits carbon availability and affects downstream biofilm formation and community structure. Applied and Environmental Microbiology. 2006; 72 (9):5702-5712 - 115.
Lammertyn E et al. Evidence for the presence of legionella bacteriophages in environmental water samples. Microbial Ecology. 2008; 56 (1):191-197 - 116.
Hughes KA, Sutherland IW, Jones MV. Biofilm susceptibility to bacteriophage attack: The role of phage-borne polysaccharide depolymerase. Microbiology. 1998; 144 (Pt 11):3039-3047 - 117.
Raftery TD et al. Discrete nanoparticles induce loss of legionella pneumophila biofilms from surfaces. Nanotoxicology. 2014; 8 (5):477-484 - 118.
Subbiahdoss G et al. Magnetic targeting of surface-modified superparamagnetic iron oxide nanoparticles yields antibacterial efficacy against biofilms of gentamicin-resistant staphylococci. Acta Biomaterialia. 2012; 8 (6):2047-2055 - 119.
Taylor EN et al. Superparamagnetic iron oxide nanoparticles (SPION) for the treatment of antibiotic-resistant biofilms. Small. 2012; 8 (19):3016-3027 - 120.
Berjeaud JM et al. Legionella pneumophila: The paradox of a highly sensitive opportunistic waterborne pathogen able to persist in the environment. Frontiers in Microbiology. 2016; 7 :486 - 121.
Wright JB, Ruseska I, Costerton JW. Decreased biocide susceptibility of adherent legionella pneumophila. The Journal of Applied Bacteriology. 1991; 71 (6):531-538 - 122.
Bezanson G et al. In situ colonization of polyvinyl chloride, brass, and copper by legionella pneumophila. Canadian Journal of Microbiology. 1992; 38 (4):328-330 - 123.
Turetgen I, Cotuk A. Monitoring of biofilm-associated legionella pneumophila on different substrata in model cooling tower system. Environmental Monitoring and Assessment. 2007; 125 (1-3):271-279 - 124.
Rogers J et al. Influence of plumbing materials on biofilm formation and growth of legionella pneumophila in potable water systems. Applied and Environmental Microbiology. 1994; 60 (6):1842-1851 - 125.
Donlan RM et al. Legionella pneumophila associated with the protozoan Hartmannella vermiformis in a model multi-species biofilm has reduced susceptibility to disinfectants. Biofouling. 2005; 21 (1):1-7 - 126.
Liu Z et al. Effect of flow regimes on the presence of legionella within the biofilm of a model plumbing system. Journal of Applied Microbiology. 2006; 101 (2):437-442 - 127.
Lehtola MJ et al. Survival of Mycobacterium avium, legionella pneumophila, Escherichia coli, and caliciviruses in drinking water-associated biofilms grown under high-shear turbulent flow. Applied and Environmental Microbiology. 2007; 73 (9):2854-2859 - 128.
van der Kooij D, Veenendaal HR, Scheffer WJ. Biofilm formation and multiplication of legionella in a model warm water system with pipes of copper, stainless steel and cross-linked polyethylene. Water Research. 2005; 39 (13):2789-2798