BACKGROUND
bacterial biofilm, a complex community of surface-associated cells surrounded by a self-produced polymer matrix consisting mostly of polysaccharides and dna can form at infection sites and promote chronic infection .
biofilm increases bacterial resistance to the host immune system, provides a place for development of resistant microorganisms and is associated with increased resistance to exogenous antibiotic treatment .
therefore, once established, biofilm infections are nearly impossible to eradicate  <cit> .
biofilm formation involves the production of an extracellular matrix, but the composition of this matrix is not well defined.
in pseudomonas aeruginosa pa <dig>  decreased production of extracellular polymers reduces static biofilm development  <cit> .
an increasing number of studies support the hypothesis that dna, f-actin, and possibly other filamentous polymers released from host inflammatory cells, as well as products of bacterial autolysis, trigger genetic changes in planktonic bacteria that initiate the formation of biofilm  <cit> .
extracellular dna and f-actin have been shown to function as a structural support for bacterial biofilm architecture  <cit>  and have been proposed as therapeutic targets to prevent biofilm growth  <cit> .
culturing pseudomonas aeruginosa  in settings that include neutrophils enhances formation of biofilms by stimulating the expression of alginate  <cit> .
recently, extracellular dna was found to smooth the progress of efficient traffic flow of pa cells throughout the complex matrix of biofilm by maintaining coherent cell alignment, thereby avoiding traffic jams and ensuring an efficient supply of cells to the migrating front  <cit> .
however, biofilm formation and swarming by clinical isolates of pa were found to be negatively associated  <cit> .
another consequence of negatively-charged polymers such as dna and f-actin present at infection sites results from their ability to bind and inactivate host-derived cationic antibacterial molecules  <cit> .
therefore, poly-anionic filamentous viruses produced by pseudomonas, which are important for the virulence of these pathogens in humans, might inactivate host antibacterial molecules by similar mechanisms.
the pa strain pao <dig> strongly up-regulates genes encoding pf1-like phages at the start of biofilm formation, and pf1-like virions are present at  <dig> to  <dig> fold higher levels in biofilms when compared with planktonic pa cultures  <cit> .
the pf <dig> phage exists largely as bundles of long filamentous phages extending from the bacterial surface  <cit> .
bundle formation was previously found to be mediated by polyvalent counterions, including cationic host defense molecules  <cit> .
a repeatable pattern of cell death and lysis that occurs in biofilms during the normal course of development is also phage-dependent, and phage-mediated cell death is an important mechanism of differentiation inside microcolonies that facilitates dispersal of a subpopulation of surviving cells  <cit> .
this report indicates that addition of diverse natural polyelectrolytes, including purified pf <dig> bacteriophage, to different bacteria or candida albicans cultures results in increased biofilm formation.
the effects of pf <dig> on biofilm formation by bacterial strains that it cannot infect suggests that the physicochemical properties of pf <dig> and similar polyelectrolytes, rather than any specific biological effect of the bacteriophage on the bacteria is required for it to support biofilm formation by different microorganisms.
RESULTS
polyelectrolyte-induced formation of microorganisms’ biofilm
in agreement with previous reports  <cit>  f-actin increased biofilm formation by pa pao <dig> on glass .
increased chemiluminescence of pa xen <dig> bacteria culture after 48 h growth in the presence of f-actin or dna was observed .
dna staining with yoyo- <dig> revealed an increased concentration of dna in s. aureus xen <dig> biofilm formed in the presence of exogenous dna .
this observation suggests that bacteria might use their own and likely other species’ extracellular dna to form a biofilm matrix.
increased attachment of pa pao <dig> to the cytoskeleton fraction of a <dig> cells attached to the coverglass surface after triton x- <dig> treatment indicates that bacteria are able to bind the f-actin network .
compared to dna and pf <dig>  f-actin has a stronger stimulatory effect on biofilm mass of pa xen <dig> and s. aureus xen <dig> .
among all tested bacteria strains, the largest increase in biofilm production was observed after 48 h for b. subtilis growth in the presence of  <dig>  and 1 mg/ml pf <dig>  .
a statistically significant increase in biofilm formation was also observed at 48 h in pa p <dig> culture after addition of  <dig>  and 1 mg/ml pf <dig> , in e coli mg <dig> culture with addition of 1 mg/ml pf <dig>  and e.coli rs <dig> culture with addition of  <dig>  and 1 mg/ml pf <dig>  .
the observed differences between the amounts of biofilm formed in the presence of pf <dig> bacteriophage for different bacterial strains might be a result of growth rate differences.
dna, f-actin, neurofilaments and vimentin are all anionic polyelectrolyte filaments present within the cellular and extracellular space, that have large net negative charge densities distributed over their surfaces and all promote biofilm formation .
however, there are some differences between their activity that may result from filament properties or the growth of different bacteria strains.
neurofilaments have little effect on pa xen <dig> biofilm formation compared to their effect on s. aureus xen <dig>  which is more than doubled in the presence of neurofilaments at a concentration of  <dig>  mg/ml.
vimentin slightly increases biofilm formation of both pa xen <dig> and s. aureus xen <dig> .
polyelectrolyte-induced biofilm formation was also observed for the fungus c. albicans  <dig>  which is a frequent cause of fungal infection in humans.
the fungal biofilm matrix is mostly produced by the fungal cells themselves and is composed of different types of biopolymers  <cit> .
as shown in fig.
<dig>  dna, pf <dig>  f-actin and nfs all increase the formation of c. albicans biofilm.
among these polyelectrolytes, the strongest activity was observed for dna, pf <dig>  f-actin, and nfs .
at the tested concentration range  nfs reveal the potential to promote c. albicans biofilm formation only at low concentrations.
at a concentration greater than  <dig>  mg/ml, nfs decrease the amount of biofilm formed, an effect that might be related to their high negative charge density.
at a high concentration nfs might function as neutrophil extracellular traps .fig.
<dig> bacterial biofilm formation in the presence of f-actin and dna.
a arrows indicate f-actin filaments stained with rhodamine-phalloidin and attached to a glass slide coated with poly-lysine .
b biofilm mass of pseudomonas aeruginosa pao <dig> formed in the presence of f-actin.
c chemiluminescence of pseudomonas aeruginosa xen <dig> 48 h after bacteria addition to lb broth  containing f-actin  or dna  at concentrations of  <dig> ,  <dig>  and  <dig>  mg ml − <dig> respectively.
d dna staining  of staphylococcus aureus xen <dig> biofilm after 48 h growth with and without the presence of dna.
e f-actin filaments of lung epithelial a <dig> cytoskeleton stained with rhodamine-phalloidin .
f
pseudomonas aeruginosa pao <dig> cells preferentially attached to the cytoskeleton of a <dig> cell remnants
fig.
<dig> f-actin, dna and pf <dig> bacteriophages increase staphylococcus aureus xen <dig> and pseudomonas aeruginosa xen <dig> biofilm formation.
panels a and b indicate biofilm mass assessed with crystal violet staining at  <dig> and 48 h time points.
*significantly increased compared to control
fig.
<dig> pf1-mediated increase of biofilm formation.
biofilm formation of pseudomonas aeruginosa p <dig> , bacillus subtilis atcc  <dig> , escherichia coli mg <dig>  and escherichia coli rs <dig>  in the presence of pf <dig>  biofilm mass was assessed using crystal violet staining at  <dig> and 48 h time points.
*significantly increased compared to control
fig.
<dig> biofilm formation of c. albicans.
increase of c. albicans  <dig> biofilm formation in the presence of dna , f-actin , pf <dig>  and nfs  .
*significantly different compared to control
increase of p. aeruginosa swarming activity in the presence of polyelectrolytes
bacterial swarming motility and production of exopolysaccharides both contribute to biofilm formation, yet it is unclear how bacteria coordinate these two processes  <cit> .
for some bacteria, the ability to swarm positively correlates with production of exopolysaccharides  <cit> .
in contrast, alginate oligomers  were found to bind to the bacterial surface, modulate surface charge, induce microbial aggregation, and inhibit swarming motility  <cit> .
figure  <dig> shows the morphology of a p. aeruginosa xen <dig> biofilm that develops in the presence of different biopolymers.
at the macroscopic level, a more fragmented pattern of growth was observed in the presence of f-actin, compared to uniform growth in dna- or pf1-containing samples.
as indicated by the arrow in fig.
<dig>  on the edges of the biofilm where the swarming assures spreading of bacteria, more rounded structures less than 10 μm in size are observed in substrates containing biopolymers compared to control substrates.
quantitative analysis of biofilm indicates that all tested biopolymers increase swarming activity of pa xen <dig>  among these biopolymers, there is a higher average increase of swarming area for substrates containing dna than f-actin or pf <dig> at the higher concentrations .
in agreement with our study, recent results indicate that among the tested swarming mutants, a large range of biofilm formation levels was observed  <cit> .fig.
<dig> morphology of pseudomonas aeruginosa xen <dig> biofilm growth on agar with addition of dna, f-actin and pf <dig> bacteriophage.
in the presence of different biopolymers , after 16 h of bacterial growth, the swarming edges show some similar features .
developing area of spreading pa biofilm due to swarming activity was assessed using image gauge software .
*significantly different compared to control
lower mass of biofilm formed in the presence of dnase i
two clinically important biofilm-forming bacterial pathogens, pa and s. aureus were used to assess the effects of dnase i and cationic antibacterial agents on biofilm mass.
addition of pulmozyme  at  <dig>  μg/ml significantly decreases the biofilm mass of both pathogens grown for 48 h with and without dna .
in an earlier study, the addition of poly was found to reduce adhered microflora and decrease dental plaque formation  <cit> .
the combination of dnase i and poly decreased pa biofilm formed in the presence of activated neutrophils by  <dig> % on hydrogel contact lenses  <cit> , and disrupted mature pa biofilm  <cit> .
in our experimental settings, poly decreased biofilm formation but the effect did not reach a statistically significant level .
this difference might potentially be associated with the length of polymer used.
on the other hand, in accordance with previous observations that the polycationic antimicrobial peptide ll- <dig> blocks biofilm formation at concentrations below its mic,  <cit>  decreased biofilm mass of both pathogens in the presence of ll- <dig> peptide  was observed.
a similar decrease was found in the presence of the cationic antibacterial steroid ceragenin csa- <dig> .fig.
<dig> biofilm formation in the presence of dna and dnase i. pseudomonas aeruginosa xen  <dig>  and staphylococcus aureus xen  <dig>  biofilm at 48 h in 50% lb with dna  <dig>  mg/ml in the absence/presence of dnase i  and in the presence of ll- <dig> or csa- <dig> .
inhibitory effect of dnase was compared to the effect of csa- <dig> and ll- <dig> .
*significantly different compared to control
discussion
accumulation and death of neutrophils recruited in response to pathogen invasion and tissue destruction release various negatively-charged biopolymers including dna, vimentin, and f-actin.
destruction of neuronal cells can be expected to release nfs in addition to f-actin and dna, whereas damaged muscle cells might predominantly release actin.
bacteria also support the accumulation of extracellular anionic biopolymers since they can release exopolysaccharides, bacterial dna, as well as different filamentous phage.
a growing body of evidence indicates that these biopolymers can interfere with host immunoresponse to infections.
extracellular dna  is a major structural component in many biofilms of pathogenic bacteria  <cit> .
additionally, the functional dna binding-uptake system that can be inhibited by the presence of dnase l  <cit> , dna-induced changes in gene expression  <cit> , and sphingomyelinase-mediated cross-linking of edna in the biofilm skeletal framework  <cit>  are all involved in biofilm formation by different bacterial pathogens.
results of our study indicate that the ability to stimulate biofilm formation might be a common feature of negatively charged biopolymers, including pf1-like phages expressed by pa strains preferentially infecting cf patients.
however, there are conflicting interpretations as to whether production of the filamentous phage virions encoded within p. aeruginosa as they colonize the airway increase the virulence of p. aeruginosa strains.
the increased production of biofilm in the presence of pf <dig> suggests that phage expression should be considered as a factor that increases the virulence of pseudomonas.
determining the relevant concentration range of phage and other polyelectrolytes is guided by several considerations.
infected, purulent body fluids such as cystic fibrosis sputum can contain as much as 50 mg ml− <dig> dna and 10 mg ml−1 f-actin.
since pf <dig> is not lytic and diffuses very slowly from its site of production, the relevant virus concentration is that adjacent to the bacteria, as seen in  <cit> .
quantitative studies of the rate or extent of pf <dig>  pf <dig>  or pf <dig> production by pseudomonas strains have not yet been reported, but e. coli can produce  <dig> copies of the structurally similar 800 nm long filamentous phage m <dig> per hour  <cit> .
making the conservative estimate that a  <dig>  μm x 2 μm cylindrical pseudomonas produces  <dig> viruses extending from the bacterial surface, and using the fact that a polymer of length 2 μm and persistence length 2 μm has an end-to-end distance of  <dig>  μm  <cit> , the local concentration of pf <dig> within the zone  <dig>  μm away from the bacterial surface is approximately 1 mg ml− <dig>  this concentration is within the range at which pf <dig> promotes biofilm growth.
therefore  between  <dig>  and 5 mg ml− <dig> is likely to be relevant to a purulent setting.
these findings also indicate that the physicochemical properties of filamentous bacteriophage, and its concentration, rather than the ability of pf <dig> to infect and propagate in bacteria, are sufficient to promote biofilm growth.
pf <dig> has a very similar size, shape, and charge density as f-actin and aggregates similarly with multivalent cations.
these features might explain the strong ability of both polymers to induce biofilm formation  <cit> , as well as that of neurofilaments and vimentin  <cit> .
in agreement with recent studies showing an increase of c. albicans biofilm formation induced by its own dna as well as dna released from bacteria  <cit> , we observed that dna and other natural polyelectrolytes such as f-actin, pf <dig> and nfs can all stimulate this process.
the dose-dependent effect recorded for nfs  was previously reported for dna  <cit> .
the effect of anionic biopolymers to promote biofilm formation may depend on their effect on swarming mobility.
many bacteria move in groups, in a mode described as swarming to colonize surfaces and form a biofilm to survive external stresses, including exposure to antibiotics  <cit> .
considering the possibility of charge-driven interactions, antibiotic resistance might result from the ability to sequester positively-charged antibiotics by negatively-charged polymeric components  <cit>  of the biofilm network before the antibiotics reach and insert into bacterial cells.
this mode of bactericidal agent inactivation affects natural host defense cationic peptides such as cathelicidin ll- <dig>
CONCLUSIONS
the presence of polyelectrolytes at infection sites such as dna, f-actin, neurofilaments and pf <dig> bacteriophage is likely to promote biofilm formation.
however, the mass of developing biofilm in the presence of the same kind of polyelectrolytes varies among different microorganism strains.

 bacterial biofilm, a complex community of surface-associated cells surrounded by a self-produced polymer matrix consisting mostly of polysaccharides and dna can form at infection sites and promote chronic infection. biofilm increases bacterial resistance to the host immune system, provides a place for development of resistant microorganisms and is associated with increased resistance to exogenous antibiotic treatment. therefore, once established, biofilm infections are nearly impossible to eradicate. biofilm formation involves the production of an extracellular matrix, but the composition of this matrix is not well defined. in pseudomonas aeruginosa pa decreased production of extracellular polymers reduces static biofilm development. an increasing number of studies support the hypothesis that dna, f-actin, and possibly other filamentous polymers released from host inflammatory cells, as well as products of bacterial autolysis, trigger genetic changes in planktonic bacteria that initiate the formation of biofilm. extracellular dna and f-actin have been shown to function as a structural support for bacterial biofilm architecture and have been proposed as therapeutic targets to prevent biofilm growth. culturing pseudomonas aeruginosa in settings that include neutrophils enhances formation of biofilms by stimulating the expression of alginate. recently, extracellular dna was found to smooth the progress of efficient traffic flow of pa cells throughout the complex matrix of biofilm by maintaining coherent cell alignment, thereby avoiding traffic jams and ensuring an efficient supply of cells to the migrating front. however, biofilm formation and swarming by clinical isolates of pa were found to be negatively associated. another consequence of negatively-charged polymers such as dna and f-actin present at infection sites results from their ability to bind and inactivate host-derived cationic antibacterial molecules. therefore, poly-anionic filamentous viruses produced by pseudomonas, which are important for the virulence of these pathogens in humans, might inactivate host antibacterial molecules by similar mechanisms. the pa strain pao strongly up-regulates genes encoding pf1-like phages at the start of biofilm formation, and pf1-like virions are present at to fold higher levels in biofilms when compared with planktonic pa cultures. the pf phage exists largely as bundles of long filamentous phages extending from the bacterial surface. bundle formation was previously found to be mediated by polyvalent counterions, including cationic host defense molecules. a repeatable pattern of cell death and lysis that occurs in biofilms during the normal course of development is also phage-dependent, and phage-mediated cell death is an important mechanism of differentiation inside microcolonies that facilitates dispersal of a subpopulation of surviving cells. this report indicates that addition of diverse natural polyelectrolytes, including purified pf bacteriophage, to different bacteria or candida albicans cultures results in increased biofilm formation. the effects of pf on biofilm formation by bacterial strains that it cannot infect suggests that the physicochemical properties of pf and similar polyelectrolytes, rather than any specific biological effect of the bacteriophage on the bacteria is required for it to support biofilm formation by different microorganisms.  polyelectrolyte-induced formation of microorganisms’ biofilm in agreement with previous reports f-actin increased biofilm formation by pa pao on glass. increased chemiluminescence of pa xen bacteria culture after 48 h growth in the presence of f-actin or dna was observed. dna staining with yoyo- revealed an increased concentration of dna in s. aureus xen biofilm formed in the presence of exogenous dna. this observation suggests that bacteria might use their own and likely other species’ extracellular dna to form a biofilm matrix. increased attachment of pa pao to the cytoskeleton fraction of a cells attached to the coverglass surface after triton x- treatment indicates that bacteria are able to bind the f-actin network. compared to dna and pf f-actin has a stronger stimulatory effect on biofilm mass of pa xen and s. aureus xen. among all tested bacteria strains, the largest increase in biofilm production was observed after 48 h for b. subtilis growth in the presence of and 1 mg/ml pf. a statistically significant increase in biofilm formation was also observed at 48 h in pa p culture after addition of and 1 mg/ml pf, in e coli mg culture with addition of 1 mg/ml pf and e.coli rs culture with addition of and 1 mg/ml pf. the observed differences between the amounts of biofilm formed in the presence of pf bacteriophage for different bacterial strains might be a result of growth rate differences. dna, f-actin, neurofilaments and vimentin are all anionic polyelectrolyte filaments present within the cellular and extracellular space, that have large net negative charge densities distributed over their surfaces and all promote biofilm formation. however, there are some differences between their activity that may result from filament properties or the growth of different bacteria strains. neurofilaments have little effect on pa xen biofilm formation compared to their effect on s. aureus xen which is more than doubled in the presence of neurofilaments at a concentration of  mg/ml. vimentin slightly increases biofilm formation of both pa xen and s. aureus xen. polyelectrolyte-induced biofilm formation was also observed for the fungus c. albicans which is a frequent cause of fungal infection in humans. the fungal biofilm matrix is mostly produced by the fungal cells themselves and is composed of different types of biopolymers. as shown in fig.  dna, pf f-actin and nfs all increase the formation of c. albicans biofilm. among these polyelectrolytes, the strongest activity was observed for dna, pf f-actin, and nfs. at the tested concentration range nfs reveal the potential to promote c. albicans biofilm formation only at low concentrations. at a concentration greater than  mg/ml, nfs decrease the amount of biofilm formed, an effect that might be related to their high negative charge density. at a high concentration nfs might function as neutrophil extracellular traps.fig. bacterial biofilm formation in the presence of f-actin and dna. a arrows indicate f-actin filaments stained with rhodamine-phalloidin and attached to a glass slide coated with poly-lysine. b biofilm mass of pseudomonas aeruginosa pao formed in the presence of f-actin. c chemiluminescence of pseudomonas aeruginosa xen 48 h after bacteria addition to lb broth containing f-actin or dna at concentrations of, and  mg ml − respectively. d dna staining of staphylococcus aureus xen biofilm after 48 h growth with and without the presence of dna. e f-actin filaments of lung epithelial a cytoskeleton stained with rhodamine-phalloidin. f pseudomonas aeruginosa pao cells preferentially attached to the cytoskeleton of a cell remnants fig. f-actin, dna and pf bacteriophages increase staphylococcus aureus xen and pseudomonas aeruginosa xen biofilm formation. panels a and b indicate biofilm mass assessed with crystal violet staining at and 48 h time points. *significantly increased compared to control fig. pf1-mediated increase of biofilm formation. biofilm formation of pseudomonas aeruginosa p, bacillus subtilis atcc, escherichia coli mg and escherichia coli rs in the presence of pf biofilm mass was assessed using crystal violet staining at and 48 h time points. *significantly increased compared to control fig. biofilm formation of c. albicans. increase of c. albicans biofilm formation in the presence of dna, f-actin, pf and nfs. *significantly different compared to control increase of p. aeruginosa swarming activity in the presence of polyelectrolytes bacterial swarming motility and production of exopolysaccharides both contribute to biofilm formation, yet it is unclear how bacteria coordinate these two processes. for some bacteria, the ability to swarm positively correlates with production of exopolysaccharides. in contrast, alginate oligomers were found to bind to the bacterial surface, modulate surface charge, induce microbial aggregation, and inhibit swarming motility. figure  shows the morphology of a p. aeruginosa xen biofilm that develops in the presence of different biopolymers. at the macroscopic level, a more fragmented pattern of growth was observed in the presence of f-actin, compared to uniform growth in dna- or pf1-containing samples. as indicated by the arrow in fig.  on the edges of the biofilm where the swarming assures spreading of bacteria, more rounded structures less than 10 μm in size are observed in substrates containing biopolymers compared to control substrates. quantitative analysis of biofilm indicates that all tested biopolymers increase swarming activity of pa xen among these biopolymers, there is a higher average increase of swarming area for substrates containing dna than f-actin or pf at the higher concentrations. in agreement with our study, recent results indicate that among the tested swarming mutants, a large range of biofilm formation levels was observed.fig. morphology of pseudomonas aeruginosa xen biofilm growth on agar with addition of dna, f-actin and pf bacteriophage. in the presence of different biopolymers, after 16 h of bacterial growth, the swarming edges show some similar features. developing area of spreading pa biofilm due to swarming activity was assessed using image gauge software. *significantly different compared to control lower mass of biofilm formed in the presence of dnase i two clinically important biofilm-forming bacterial pathogens, pa and s. aureus were used to assess the effects of dnase i and cationic antibacterial agents on biofilm mass. addition of pulmozyme at  μg/ml significantly decreases the biofilm mass of both pathogens grown for 48 h with and without dna. in an earlier study, the addition of poly was found to reduce adhered microflora and decrease dental plaque formation. the combination of dnase i and poly decreased pa biofilm formed in the presence of activated neutrophils by % on hydrogel contact lenses, and disrupted mature pa biofilm. in our experimental settings, poly decreased biofilm formation but the effect did not reach a statistically significant level. this difference might potentially be associated with the length of polymer used. on the other hand, in accordance with previous observations that the polycationic antimicrobial peptide ll- blocks biofilm formation at concentrations below its mic, decreased biofilm mass of both pathogens in the presence of ll- peptide was observed. a similar decrease was found in the presence of the cationic antibacterial steroid ceragenin csa-.fig. biofilm formation in the presence of dna and dnase i. pseudomonas aeruginosa xen and staphylococcus aureus xen biofilm at 48 h in 50% lb with dna  mg/ml in the absence/presence of dnase i and in the presence of ll- or csa-. inhibitory effect of dnase was compared to the effect of csa- and ll-. *significantly different compared to control discussion accumulation and death of neutrophils recruited in response to pathogen invasion and tissue destruction release various negatively-charged biopolymers including dna, vimentin, and f-actin. destruction of neuronal cells can be expected to release nfs in addition to f-actin and dna, whereas damaged muscle cells might predominantly release actin. bacteria also support the accumulation of extracellular anionic biopolymers since they can release exopolysaccharides, bacterial dna, as well as different filamentous phage. a growing body of evidence indicates that these biopolymers can interfere with host immunoresponse to infections. extracellular dna is a major structural component in many biofilms of pathogenic bacteria. additionally, the functional dna binding-uptake system that can be inhibited by the presence of dnase l, dna-induced changes in gene expression, and sphingomyelinase-mediated cross-linking of edna in the biofilm skeletal framework are all involved in biofilm formation by different bacterial pathogens. results of our study indicate that the ability to stimulate biofilm formation might be a common feature of negatively charged biopolymers, including pf1-like phages expressed by pa strains preferentially infecting cf patients. however, there are conflicting interpretations as to whether production of the filamentous phage virions encoded within p. aeruginosa as they colonize the airway increase the virulence of p. aeruginosa strains. the increased production of biofilm in the presence of pf suggests that phage expression should be considered as a factor that increases the virulence of pseudomonas. determining the relevant concentration range of phage and other polyelectrolytes is guided by several considerations. infected, purulent body fluids such as cystic fibrosis sputum can contain as much as 50 mg ml− dna and 10 mg ml−1 f-actin. since pf is not lytic and diffuses very slowly from its site of production, the relevant virus concentration is that adjacent to the bacteria, as seen in. quantitative studies of the rate or extent of pf pf or pf production by pseudomonas strains have not yet been reported, but e. coli can produce copies of the structurally similar 800 nm long filamentous phage m per hour. making the conservative estimate that a  μm x 2 μm cylindrical pseudomonas produces viruses extending from the bacterial surface, and using the fact that a polymer of length 2 μm and persistence length 2 μm has an end-to-end distance of  μm, the local concentration of pf within the zone  μm away from the bacterial surface is approximately 1 mg ml− this concentration is within the range at which pf promotes biofilm growth. therefore between and 5 mg ml− is likely to be relevant to a purulent setting. these findings also indicate that the physicochemical properties of filamentous bacteriophage, and its concentration, rather than the ability of pf to infect and propagate in bacteria, are sufficient to promote biofilm growth. pf has a very similar size, shape, and charge density as f-actin and aggregates similarly with multivalent cations. these features might explain the strong ability of both polymers to induce biofilm formation, as well as that of neurofilaments and vimentin. in agreement with recent studies showing an increase of c. albicans biofilm formation induced by its own dna as well as dna released from bacteria, we observed that dna and other natural polyelectrolytes such as f-actin, pf and nfs can all stimulate this process. the dose-dependent effect recorded for nfs was previously reported for dna. the effect of anionic biopolymers to promote biofilm formation may depend on their effect on swarming mobility. many bacteria move in groups, in a mode described as swarming to colonize surfaces and form a biofilm to survive external stresses, including exposure to antibiotics. considering the possibility of charge-driven interactions, antibiotic resistance might result from the ability to sequester positively-charged antibiotics by negatively-charged polymeric components of the biofilm network before the antibiotics reach and insert into bacterial cells. this mode of bactericidal agent inactivation affects natural host defense cationic peptides such as cathelicidin ll-  the presence of polyelectrolytes at infection sites such as dna, f-actin, neurofilaments and pf bacteriophage is likely to promote biofilm formation. however, the mass of developing biofilm in the presence of the same kind of polyelectrolytes varies among different microorganism strains. 
the presence of polyelectrolytes at infection sites is likely to promote biofilm growth and bacterial swarming. biofilm formation is associated with various aspects of bacterial and fungal infection. this study was designed to assess the impact of diverse natural polyelectrolytes, such as dna, f-actin, neurofilaments, vimentin and purified pf bacteriophage on biofilm formation and swarming motility of select pathogens including pseudomonas aeruginosa associated with lung infections in cf patients. the bacteriophage pf significantly increased biofilm mass produced by pseudomonas aeruginosa p escherichia coli rs and bacillus subtilis atcc dna, f-actin, nfs and pf also increased biofilm mass of the fungal c. albicans strain. albicansfilamentous bacteriophagesdnaf-actinbiofilm massissue-copyright-statement© the author 2015 addition of f-actin, dna or pf bacteriophage to % agar plates increased swarming motility of pseudomonas aeruginosa xen 
 biofilm formation is associated with various aspects of bacterial and fungal infection. this study was designed to assess the impact of diverse natural polyelectrolytes, such as dna, f-actin, neurofilaments, vimentin and purified pf bacteriophage on biofilm formation and swarming motility of select pathogens including pseudomonas aeruginosa associated with lung infections in cf patients.  the bacteriophage pf significantly increased biofilm mass produced by pseudomonas aeruginosa p escherichia coli rs and bacillus subtilis atcc dna, f-actin, nfs and pf also increased biofilm mass of the fungal c. albicans strain. addition of f-actin, dna or pf bacteriophage to % agar plates increased swarming motility of pseudomonas aeruginosa xen  the presence of polyelectrolytes at infection sites is likely to promote biofilm growth and bacterial swarming. keywords bacteriac. albicansfilamentous bacteriophagesdnaf-actinbiofilm massissue-copyright-statement© the author 2015 