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PubMed2006

Role of cohesion in the material description of biofilms.

Biofilm structure plays an important role in biofilm function and control. It is thus important to determine the extent to which mechanics may determine structure in biofilms. We consider a generic qualitative constitutive description of biofilm incorporating as assumptions a small number of fundamental physical properties of biofilm viscoelasticity and cohesion. Implications of cohesive energy on biofilm structure are then explored. Steady solutions and energy minima are studied and it is demonstrated that cohesion energy leads naturally to a free surface film state. It is found that in many circumstances, biofilms could be subject to heterogeneity formation via spinodal decomposition. Such material heterogeneity may have important implications for structural stability in biofilms both on short and long time scales.

Bacterial Physiological Phenomena↗

PubMed2003

Pseudomonas aeruginosa-plant root interactions. Pathogenicity, biofilm formation, and root exudation.

Pseudomonas aeruginosa is an opportunistic human pathogen capable of forming a biofilm under physiological conditions that contributes to its persistence despite long-term treatment with antibiotics. Here, we report that pathogenic P. aeruginosa strains PAO1 and PA14 are capable of infecting the roots of Arabidopsis and sweet basil (Ocimum basilicum), in vitro and in the soil, and are capable of causing plant mortality 7 d postinoculation. Before plant mortality, PAO1 and PA14 colonize the roots of Arabidopsis and sweet basil and form a biofilm as observed by scanning electron microscopy, phase contrast microscopy, and confocal scanning laser microscopy. Upon P. aeruginosa infection, sweet basil roots secrete rosmarinic acid (RA), a multifunctional caffeic acid ester that exhibits in vitro antibacterial activity against planktonic cells of both P. aeruginosa strains with a minimum inhibitory concentration of 3 microg mL(-1). However, in our studies RA did not attain minimum inhibitory concentration levels in sweet basil's root exudates before P. aeruginosa formed a biofilm that resisted the microbicidal effects of RA and ultimately caused plant mortality. We further demonstrated that P. aeruginosa biofilms were resistant to RA treatment under in vivo and in vitro conditions. In contrast, induction of RA secretion by sweet basil roots and exogenous supplementation of Arabidopsis root exudates with RA before infection conferred resistance to P. aeruginosa. Under the latter conditions, confocal scanning laser microscopy revealed large clusters of dead P. aeruginosa on the root surface of Arabidopsis and sweet basil, and biofilm formation was not observed. Studies with quorum-sensing mutants PAO210 (DeltarhlI), PAO214 (DeltalasI), and PAO216 (DeltalasI DeltarhlI) demonstrated that all of the strains were pathogenic to Arabidopsis, which does not naturally secrete RA as a root exudate. However, PAO214 was the only pathogenic strain toward sweet basil, and PAO214 biofilm appeared comparable with biofilms formed by wild-type strains of P. aeruginosa. Our results collectively suggest that upon root colonization, P. aeruginosa forms a biofilm that confers resistance against root-secreted antibiotics.

Anti-Bacterial Agents↗

PubMed2004

The effects of substratum on the pH response of Streptococcus mutans biofilms and on the susceptibility to 0.2% chlorhexidine.

Antimicrobial agents are now being studied in bacterial biofilms rather than in suspensions. However, no data are available whether the choice of substratum influences biofilm properties or the assessment of antimicrobial efficacy. This study compared dentin and polyacrylate (PA) grooves as substratum for biofilm formation on pH profiles after sugar challenge, as well as biofilm susceptibility to chlorhexidine. Streptococcus mutans biofilms were formed in a constant depth film fermenter (CDFF) by alternate pulsing with sucrose solutions and bacterial growth medium. Spatial and temporal pH profiles were measured using a pH microelectrode outside the CDFF in a flow reactor. Also, 15-d biofilms were treated with either water or 0.2% chlorhexidine and tested for total viable counts and organic acid content. The results show that in PA grooves, compared with dentin grooves, minimum pH was lower but recovered faster after a sucrose pulse. The pH response to sugar application decreased with the age of the biofilm more in PA than in dentin grooves. Chlorhexidine treatment in PA grooves gave greater reductions in viable counts and acid formation than in dentin. We conclude that the nature of the substratum not only affects metabolic activity of biofilms but also their susceptibility to antimicrobials.

Acrylic Resins↗

PubMed1995

A simple in vitro model for growth control of bacterial biofilms.

The perfused biofilm fermenter was found to be unsuitable for the long-term culture and growth rate control of Staphylococcus aureus and Pseudomonas aeruginosa biofilms. In a simplified approach, biofilms of these organisms were grown within Sorbarod filter plugs which were perfused with culture medium. Pseudo-steady states were established which were stable over several days at which the growth rate of the biofilm was reproducible, measurable and significantly slower than in broth culture. Environmental scanning electron microscopy of dissected Sorbarods demonstrated an association of cells with the surfaces of individual cellulose fibres, and growth characteristic of biofilms. Relatively high cell numbers recovered from the Sorbarod model facilitated biochemical investigations of biofilm populations and cells released spontaneously from them. SDS-PAGE demonstrated significant differences between the protein profiles of biofilm and eluted populations, which include, in Staph. aureus, the repression of a 48 kDa protein and increased expression of a 21 kDa protein relative to planktonic controls cultured at equivalent growth rates. The paper demonstrates the suitability of the approach for the culture of biofilm samples which are suitable for biochemical analysis.

Bacteriological Techniques↗

PubMed2004

Impact of cleaning and disinfection agents on biofilm structure and on microbial transfer to a solid model food.

AIM: To determine how single cells and microcolonies transfer to food from open surfaces in the meat industry. METHODS AND RESULTS: Biofilms of four bacterial strains isolated from food processing surfaces were established on stainless steel substrates conditioned with meat exudate in the presence or absence of CaCl(2). Image analysis of the biofilms showed that the addition of calcium resulted in an increase of the number and size of microcolonies with two strains: Staphylococcus sciuri and Pseudomonas fluorescens. Image analysis of the biofilms of those two strains grown in the presence of calcium was performed before and after contacts with tryptone soya agar as a solid model food. For the biofilms treated or not with a chlorinated alkaline agent, where a decrease in surface coverage occurred, it was accompanied by a decrease in the percentage of the coverage accounted for by microcolonies (P(m)). Attachment strength was greater for P. fluorescens than for S. sciuri. When the P. fluorescens biofilms were treated with a solution containing glutaraldehyde, the contacts did not modify their structure. By contrast, their treatment with chlorinated alkaline resulted, after contacts, in the smallest coverage and P(m). With S. sciuri, a decrease in coverage after contacts always occurred and was the greatest for the untreated biofilms. CONCLUSIONS: After contacts between biofilms and a solid model food, microcolonies were preferentially detached compared with single cells. A chlorinated alkaline product either decreased biofilm attachment strength (P. fluorescens) or unexpectedly increased it (S. sciuri), whereas a glutaraldehyde-based disinfectant increased both attachment strength and microcolony cohesion. SIGNIFICANCE AND IMPACT OF THE STUDY: The contaminating potential of a surface depends not only on the level of contamination but also on the nature, structure and history of the contamination.

Bacterial Adhesion↗

PubMed2006

Mucin-Pseudomonas aeruginosa interactions promote biofilm formation and antibiotic resistance.

Pseudomonas aeruginosa is an opportunistic pathogen that causes chronic lung infections in people suffering from cystic fibrosis (CF). In CF airways, P. aeruginosa forms surface-associated communities called biofilms. Compared with free-swimming cultures, biofilms resist clearance by the host immune system and display increased resistance to antimicrobial agents. In this study we developed a technique to coat surfaces with molecules that are abundant in CF airways in order to investigate their impact on P. aeruginosa biofilm development. We found that P. aeruginosa biofilm development proceeds differently on surfaces coated with the glycoprotein mucin compared with biofilm development on glass and surfaces coated with actin or DNA. Biofilms formed on mucin-coated surfaces developed large cellular aggregates and had increased tolerance to the antibiotic tobramycin compared with biofilms grown on glass. Analysis of selected mutant backgrounds in conjunction with time-lapse microscopy revealed that surface-associated motility was blocked on the mucin surface. Furthermore, our data suggest that a specific adhesin-mucin interaction immobilizes the bacterium on the surface. Together, these experiments suggest that mucin, which may serve as an attachment surface in CF airways, impacts P. aeruginosa biofilm development and function.

Anti-Bacterial Agents↗

PubMed2006

The impact of quorum sensing and swarming motility on Pseudomonas aeruginosa biofilm formation is nutritionally conditional.

The role of quorum sensing in Pseudomonas aeruginosa biofilm formation is unclear. Some researchers have shown that quorum sensing is important for biofilm development, while others have indicated it has little or no role. In this study, the contribution of quorum sensing to biofilm development was found to depend upon the nutritional environment. Depending upon the carbon source, quorum-sensing mutant strains (lasIrhlI and lasRrhlR) either exhibited a pronounced defect early in biofilm formation or formed biofilms identical to the wild-type strain. Quorum sensing was then shown to exert its nutritionally conditional control of biofilm development through regulation of swarming motility. Examination of pilA and fliM mutant strains further supported the role of swarming motility in biofilm formation. These data led to a model proposing that the prevailing nutritional conditions dictate the contributions of quorum sensing and swarming motility at a key juncture early in biofilm development.

Biofilms↗

PubMed2004

Biofilm growth of Lactobacillus species is promoted by Actinomyces species and Streptococcus mutans.

The ability of oral bacteria to integrate within a biofilm is pivotal to their survival. A dependence on the amount of biofilm growth by noncoaggregating Lactobacillus rhamnosus and Lactobacillus plantarum on coculture with Actinomyces naeslundii, Actinomyces gerencseriae, Streptococcus mutans and Veillonella parvula was investigated using an artificial-mouth culture system. Biofilm formation by the lactobacilli in mono-culture was poor. In coculture with Actinomyces species the amount of L. rhamnosus increased 7-20 times and L. plantarum 4-7 times compared to its mono-culture biofilm. S. mutans also promoted substantial biofilm growth of lactobacilli but V. parvula had no effect. We conclude that these Actinomyces species promoted growth of key Lactobacillus species in a biofilm, as did S. mutans to a smaller extent, and that the ability of individual bacteria to form mono-culture biofilms is not necessarily an indicator of their survival and pathogenic potential in a complex multispecies biofilm community.

Actinomyces↗

PubMed2004

Role of a Streptococcus gordonii copper-transport operon, copYAZ, in biofilm detachment.

Streptococcus gordonii is a pioneer oral bacterium that is associated with the initiation of dental plaque development. Located downstream of the S. gordonii adc operon, which is involved in competence and biofilm formation, were three open reading frames, designated copY, copA and copZ. These open reading frames were homologous to the copYAZ genes in Streptococcus mutans that are involved in copper homeostasis and biofilm detachment. This study examined whether copYAZ genes play any role in the biofilm formation and detachment of S. gordonii. The copY gene encodes a 143-amino acid protein homologous to the negative transcriptional regulator of a copper-transport operon, copA encodes a 748-amino acid copper-transporting P-type ATPase, and copZ encodes a 69-amino acid putative metallochaperone protein in S. mutans. Each open reading frame in the copYAZ operon in S. gordonii was inactivated by insertional mutation and the growth, biofilm formation and detachment of each mutant were examined. S. gordonii copY::specR, copA::specR, and copZ::specR mutants were able to form biofilms on both polystyrene and glass surfaces. However, inactivation of copZ and to a lesser extent copY resulted in phenotypes that were defective in biofilm detachment, which is consistent with previous observations in S. mutans and suggests that the trace element copper might influence biofilm detachment of bacterial biofilms.

Bacterial Adhesion↗

PubMed2005

Mutational analysis of the adcCBA genes in Streptococcus gordonii biofilm formation.

Streptococcus gordonii, a primary colonizer, is part of the pioneer biofilm consortium that initiates dental plaque development on tooth surfaces. An insertion of Tn917-lac transposon into the adcR gene produced a biofilm-defective phenotype. S. gordonii adcR is a regulatory gene and is part of an operon (adc) that includes three other genes, adcCBA. AdcC contains a putative consensus-binding site for adenosine triphosphate, AdcB is a putative hydrophobic membrane protein, and AdcA is a putative lipoprotein permease. Mutants were constructed by insertional inactivation in each of the three adcCBA genes and their effects on biofilm formation examined. The adcC::spec(R) and adcB::spec(R) mutations displayed a biofilm-defective phenotype, whereas the adcA::spec(R) mutant was biofilm-positive in a static polystyrene microtiter plate biofilm assay. All three mutants formed poor biofilms in a flow-cell system and were competence-defective, suggesting the adc operon plays an important role in S. gordonii biofilm formation and competence.

ATP-Binding Cassette Transporters↗

PubMed2006

Vertical distribution of nitrifying populations in bacterial biofilms from a full-scale nitrifying trickling filter.

Cryosectioned biofilm from three depths (0.5, 3.0 and 6.0 m) in a full-scale nitrifying trickling filter (NTF) were studied using fluorescence in situ hybridization (FISH). A large number of sections were used to determine how the biofilm thickness, structure and community composition varied with depth along the ammonium concentration gradient in the NTF, and how the ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) were distributed vertically within the biofilm. Both the biofilm thickness and relative biomass content of the biofilm decreased with depth, along with structural differences such as void size and surface roughness. Four AOB populations were found, with two Nitrosomonas oligotropha populations dominating at all depths. A smaller population of Nitrosomonas europaea was present only at 0.5 m, while a population of Nitrosomonas communis increased with depth. The two N. oligotropha populations showed different vertical distribution patterns within the biofilm, indicating different ecophysiologies even though they belong to the same AOB lineage. All NOB were identified as Nitrospira sp., and were generally more associated with the biofilm base than the surface-associated dominating AOB population. Additionally, a small population of anaerobic ammonia-oxidizers was found at 6.0 m, even though the biofilm was well aerated.

Ammonia↗

PubMed2006

Genetics and genomics of Candida albicans biofilm formation.

Biofilm formation by the opportunistic fungal pathogen Candida albicans is a complex process with significant consequences for human health: it contributes to implanted medical device-associated infections. Recent advances in gene expression profiling and genetic analysis have begun to clarify the mechanisms that govern C. albicans biofilm development and acquisition of unique biofilm phenotypes. Such studies have identified candidate adhesin genes, and have revealed that biofilm drug resistance is multifactorial. Newly defined cell-cell communication pathways also have profound effects on biofilm formation. Future challenges include the elucidation of the structure and function of the extracellular exopolymeric substance that surrounds biofilm cells, and the extension of in vitro biofilm observations to newly developed in vivo biofilm models.

Antifungal Agents↗

PubMed2006

Production of cellulase by Aspergillus niger biofilms developed on polyester cloth.

AIMS: To compare cellulase production by Aspergillus niger ATCC 10864 biofilms on polyester cloth and freely suspended cultures in shaken flasks and microbioreactors of bubble column type. METHODS AND RESULTS: Both shaken flasks and oxygenated microbioreactors containing 40 ml of production medium were used to compare cellulase secretion by free mycelium and biofilm cultures. Free mycelium cultures grew better in flasks than in microbioreactors producing compact and fluffy pellets, respectively, while the opposite was found for biofilm cultures without any visible change in biofilm morphology. Cellulase activities and volumetric productivities attained by biofilms in flask cultures were 70% higher than that produced by free mycelium cultures and threefold higher when biofilms were grown in microbioreactors. CONCLUSIONS: Fungal biofilms developed on polyester cloth in both flasks and microbioreactors produce higher cellulase yields and volumetric productivities than free mycelium cultures at lower biomass levels. SIGNIFICANCE AND IMPACT OF THE STUDY: The results of the present study are of commercial and biological interest. All productivity parameters revealed that fungal biofilms may be used for the production of cellulase and other proteins in various types of bioreactors. Moreover, they may be used as model systems to study differential gene expression related to cell adhesion.

Aspergillus niger↗

PubMed2006

Spent media from cultures of environmental isolates of Escherichia coli can suppress the deficiency of biofilm formation under anoxic conditions of laboratory E. coli strains.

The prevailing lifestyle of bacteria is sessile and they attach to surfaces in structures known as biofilms. In Escherichia coli, as in many other bacteria, biofilms are formed at the air-liquid interface, suggesting that oxygen has a critical role in the biofilm formation process. It has been reported that anaerobically growing E. coli laboratory strains are unable to form biofilms even after 96 h of incubation on Luria Bertani (LB) medium. After analyzing 22,000 transposon-induced and 26,000 chemically-induced mutants we failed to isolate an E. coli laboratory strain with the ability to form biofilm under anaerobic growth conditions. Notably, seven strains from a collection of E. coli isolated from different hosts and the environment had the ability to form biofilm in the absence of oxygen. Interestingly, spent medium from cultures of one strain, Souza298, can promote biofilm formation of E. coli laboratory strains growing under anaerobic conditions. Our results led us to propose that laboratory E. coli strains do not release (or synthesize) a molecule needed for biofilm formation under anoxic conditions but that they bear all the required machinery needed for this process.

Aerobiosis↗

PubMed2006

Carbohydrate-containing components of biofilms produced in vitro by some staphylococcal strains related to orthopaedic prosthesis infections.

The capacity of coagulase-negative staphylococci to colonize implanted medical devices is generally attributed to their ability to produce biofilms. Biofilm of the model strain of Staphylococcus epidermidis RP62A was shown to contain two carbohydrate-containing moieties, a linear poly-beta-(1-->6)-N-acetyl-D-glucosamine (PNAG) and teichoic acid. In the present study, we investigated several biofilm-producing staphylococci isolated from infected orthopaedic implants and characterized the composition of the laboratory-grown biofilms using chemical analysis and 1H nuclear magnetic resonance spectroscopy. Extracellular teichoic acid was produced by all strains studied. Some of the clinical strains were shown to produce biofilms with compositions similar to that of the model strain, containing a varying amount of PNAG. The chemical structure of PNAG of the clinical strains was similar to that previously described for the model strains S. epidermidis RP62A and Staphylococcus aureus MN8m, differing only in the amount of charged groups. Biofilms of the strains producing a substantial amount of PNAG were detached by dispersin B, a PNAG-degrading enzyme, while being unsusceptible to proteinase K treatment. On the other hand, some strains produced biofilms without any detectable amount of PNAG. The biofilms of these strains were dispersed by proteinase K, but not by dispersin B.

Biofilms↗

PubMed1998

Extracellular products as mediators of the formation and detachment of Pseudomonas fluorescens biofilms.

Pseudomonas fluorescens B52 produces substantial biofilms at the air/liquid/solid interface of glass coverslips clamped vertically and partly submerged in liquid medium at 21 degrees C. Biofilm formation was maximal ca. 20-50 h after inoculation of the liquid medium and as indicated by environmental scanning electron microscopy (ESEM), contained large numbers of bacterial cells that were embedded within an extensive exopolymeric matrix. Incubation beyond 50 h led to reductions in biofilm which ESEM related primarily to losses of exopolymer. Both biofilm formation and the subsequent decline in exopolymer deposition was more rapid, and occurred to greater extents, when supernatants from two-day old cultures of B52 were used as the initial growth media. The addition of N-acyl-hexanoyl homoserine lactone to fresh growth medium had a similar effect upon biofilm formation as using spent culture medium. Homoserine lactones could not be demonstrated in spent culture supernatants by an Agrobacterium tumefaciens bioassay. An exopolysaccharide lyase was detected in spend culture media taken from dense biofilm cultures whose action was specifically directed towards biofilm exopolysaccharide. Results suggest that (i) cell-cell signals such as homoserine lactones are associated with the formation of P. fluorescens biofilms, (ii) the enzymic degradation of exopolymers has a specific role in the detachment of cells under starvation conditions, and (iii) whilst short chain (C6) exogenous homoserines can trigger such response in P. fluorescens, its own signal substance is likely to possess a longer (> C8) fatty acyl chain.

4-Butyrolactone↗

PubMed2000

Heterogeneity in biofilms.

Biofilms, accumulations of microorganisms at interfaces, have been described for every aqueous system supporting life. The structure of these microbial communities ranges from monolayers of scattered single cells to thick, mucous structures of macroscopic dimensions (microbial mats; algal-microbial associations; trickling filter biofilms). During recent years the structure of biofilms from many different environments has been documented and evaluated by use of a broad variety of microscopic, physico-chemical and molecular biological techniques, revealing a generally complex 3D structure. Parallel to these investigations more and more complex mathematical models and simulations were developed to explain the development, structures, and interactions of biofilms. The forces determining the spatial structure of biofilms, including microcolonies, extracellular polymeric substances (EPS), and channels, are still the subject of controversy. To achieve conclusive explanations for the structures observed in biofilms the cooperation of both fields of investigation, modelling and experimental research, is necessary. The expanding field of molecular techniques not only allows more and more detailed documentation of the spatial distribution of species, but also of functional activities of single cells in their biofilm environment. These new methods will certainly reveal new insights in the mechanisms involved in the developmental processes involved in the formation and behavior of biofilms.

Bacteria↗

PubMed2005

Effect of two antimicrobial agents on early in situ biofilm formation.

OBJECTIVES: The aim of this observer-blind, controlled, three-cell cross-over study was to evaluate the influence of an amine fluoride/stannous fluoride (Meridol, 250 ppm; ASF) and a chlorhexidine mouthrinse (CHX; Chlorhexamed forte, 0.2%) compared with water on in situ biofilm growth. MATERIAL AND METHODS: After a professional toothcleaning seven volunteers had to wear a special acrylic appliance, in which six specimens each were inserted to allow the build-up of intra-oral biofilms. The volunteers had to rinse twice daily for 1 min. with 10 ml of the allocated mouthrinse. After 48 h of wearing, the specimens with the adhering biofilms were removed from the splints and stained with two fluorescent dyes, which selectively stain vital bacteria green and dead bacteria red. Under the confocal laser scanning microscope biofilm thickness (BT) was evaluated. To examine bacterial vitality (BV%) the biofilms were scanned (1 microm sections) and digital images were made. An image analysis program was used to calculate the mean BV as well as the BV of the single sections. After a wash-out period of 14 days a new test cycle was started. RESULTS: The use of CHX and ASF resulted in a BT of 8.4+/-4.4 mum and 15.7+/-9.9 compared with 76.7+/-29.4 mum using water. The mean vitality (in %) was reduced from 66.1+/-20.4 to 23.3+/-11.6 and 23.9+/-12.4 using CHX and ASF, respectively. Both active solutions reduced BT and BV significantly compared with water (p<0.001). Differences between the two active solutions were not significant (p>0.05). CONCLUSION: Both mouthrinses showed antibacterial and plaque-reducing properties against the in situ biofilm. The study design enables the examination of an undisturbed oral biofilm and for the first time shows the influence of antibacterial components applied under clinical conditions regarding biofilm formation.

Adult↗