The effects of magnesium, calcium, EDTA, and pH on the in vitro adhesion of Staphylococcus epidermidis to plastic

Zinc-dependent Nucleosome Reorganization by PARP2

Poly(ADP-ribose)polymerase 2 (PARP2) is a nuclear protein that acts as a DNA damage sensor; it recruits the repair enzymes to a DNA damage site and facilitates formation of the repair complex. Using single particle Förster resonance energy transfer microscopy and electrophoretic mobility shift assay (EMSA) we demonstrated that PARP2 forms complexes with a nucleosome containing different number of PARP2 molecules without altering conformation of nucleosomal DNA both in the presence and in the absence of Mg 2+ or Ca 2+ ions. In contrast, Zn 2+ ions directly interact with PARP2 inducing a local alteration of the secondary structure of the protein and PARP2-mediated, reversible structural reorganization of nucleosomal DNA. AutoPARylation activity of PARP2 is enhanced by Mg 2+ ions and modulated by Zn 2+ ions: suppressed or enhanced depending on the occupancy of two functionally different Zn 2+ binding sites. The data suggest that Zn 2+ /PARP2-induced nucleosome reorganization and transient changes in the concentration of the cations could modulate PARP2 activity and the DNA damage response.

Significance Statement

PARP2 recognizes and binds DNA damage sites, recruits the repair enzymes to these sites and facilitates formation of the repair complex. Zn 2+ -induced structural reorganization of nucleosomal DNA in the complex with PARP2, which is reported in the paper, could modulate the DNA damage response. The obtained data indicate the existence of specific binding sites of Mg 2+ and Zn 2+ ions in and/or near the catalytic domain of PARP2, which modulate strongly, differently and ion-specifically PARylation activity of PARP2, which is important for maintaining genome stability, adaptation of cells to stress, regulation of gene expression and antioxidant defense.

Differential effects of magnesium, calcium, and sodium on Listeria monocytogenes biofilm formation

Listeria monocytogenes is a gram-positive foodborne pathogen that causes outbreaks of listeriosis associated with a diverse range of foods. L. monocytogenes forms biofilms as a strategy to enhance its survival in the environment. These biofilms then provide a source of contamination in processing plant environments. Cations like magnesium, calcium, and sodium are commonly found in the environment and are important to bacteria to maintain their homeostasis. It is, therefore, valuable to understand the relationship between these cations and biofilm formation. In this study, four isolates of L. monocytogenes from seafood processing environments were used to investigate the influence of magnesium, calcium, and sodium (1, 10, and 50 mM) on biofilms. The isolates selected were defined as being either a low biofilm former, a high biofilm former, an outbreak isolate, and a persistent isolate from the seafood industry. The study showed that the divalent cations magnesium and calcium increased biofilm formation compared with the monovalent cation, sodium. Fifty mM concentrations of the divalent cations significantly enhanced biofilm formation. The cations did not have a significant effect on the initial stages of biofilm formation but appeared to influence the later stages of biofilm development.

Monitoring and imaging pH in biofilms utilizing a fluorescent polymeric nanosensor

Biofilms are ubiquitous in nature and in the man-made environment. Given their harmful effects on human health, an in-depth understanding of biofilms and the monitoring of their formation and growth are important. Particularly relevant for many metabolic processes and survival strategies of biofilms is their extracellular pH. However, most conventional techniques are not suited for minimally invasive pH measurements of living biofilms. Here, a fluorescent nanosensor is presented for ratiometric measurements of pH in biofilms in the range of pH 4.5–9.5 using confocal laser scanning microscopy. The nanosensor consists of biocompatible polystyrene nanoparticles loaded with pH-inert dye Nile Red and is surface functionalized with a pH-responsive fluorescein dye. Its performance was validated by fluorometrically monitoring the time-dependent changes in pH in E. coli biofilms after glucose inoculation at 37 °C and 4 °C. This revealed a temperature-dependent decrease in pH over a 4-h period caused by the acidifying glucose metabolism of E. coli. These studies demonstrate the applicability of this nanosensor to characterize the chemical microenvironment in biofilms with fluorescence methods.

Strontium- and peptide-modified silicate nanostructures for dual osteogenic and antimicrobial activity

Developing multifunctional nanostructures that promote bone repair while fighting infection is highly desirable in bone regenerative therapies. Previous efforts have focused on achieving one property or another by altering the chemical makeup of nanostructures or using growth factors or antibiotics. We present nanostructures with several simultaneous functional attributes including positive effects of strontium on bone formation and prevention of osteoclast differentiation along with incorporation of antimicrobial peptides (AMP) to prevent infection. To form these multifunctional nanostructures, mesoporous calcium silicate (CaMSN) was modified with high levels of strontium. For this, CaMSNs were either partially substituted (20 wt% Ca) or completely replaced with strontium (Sr) to form Sr-CaMSN or SrMSN. The mesoporous nature of these bioactive silicate nanostructures rendered a configuration for substantial AMP loading as well as their effective delivery. The physico-chemical and structural characterization of synthesized MSNs confirmed the mesoporous nature of the synthesized MSNs and their total surface area, pore size, pore volume and SBF-mediated bioactivity remained unaltered with the incorporation of Sr. However, biological evaluation confirmed that synthesized SrMSN upregulated osteogenic differentiation of mesenchymal stromal cells and significantly downregulated osteoclast differentiation. Also, the AMP-loaded MSNs prevented formation and growth of methicillin resistant Staphylococcus aureus (MRSA) biofilms. Thus, high Sr-containing AMP-loaded SrMSNs may combat MRSA-associated infection while promoting bone regeneration. The controlled availability of therapeutic Sr and AMP release as SrMSN degrade enables its potential application in bone tissue regeneration.

Evaluation of Biofilm Formation in Candida tropicalis Using a Silicone-Based Platform with Synthetic Urine Medium

Molecular mechanisms of biofilm formation in Candida tropicalis and current methods for biofilm analyses in this fungal pathogen are limited. (2) Methods: Biofilm biomass and crystal violet staining of the wild-type and each gene mutant strain of C. tropicalis were evaluated on silicone under synthetic urine culture conditions. (3) Results: Seven media were tested to compare the effects on biofilm growth with or without silicone. Results showed that biofilm cells of C. tropicalis were unable to form firm biofilms on the bottom of 12-well polystyrene plates. However, on a silicone-based platform, Roswell Park Memorial Institute 1640 (RPMI 1640), yeast nitrogen base (YNB) + 1% glucose, and synthetic urine media were able to induce strong biofilm growth. In particular, replacement of Spider medium with synthetic urine in the adherence step and the developmental stage is necessary to gain remarkably increased biofilms. Interestingly, unlike Candida albicans, the C. tropicalisROB1 deletion strain but not the other five biofilm-associated mutants did not cause a significant reduction in biofilm formation, suggesting that the biofilm regulatory circuits of the two species are divergent. (4) Conclusions: This system for C. tropicalis biofilm analyses will become a useful tool to unveil the biofilm regulatory network in C. tropicalis.

The role of magnesium in biomaterials related infections

Magnesium is currently increasing interest in the field of biomaterials. An extensive bibliography on this material in the last two decades arises from its potential for the development of biodegradable implants. In addition, many researches, motivated by this progress, have analyzed the performance of magnesium in both in vitro and in vivo assays with gram-positive and gram-negative bacteria in a very broad range of conditions. This review explores the extensive literature in recent years on magnesium in biomaterials-related infections, and discusses the mechanisms of the Mg action on bacteria, as well as the competition of Mg²⁺ and/or synergy with other divalent cations in this subject.

A biocompatible bacterial cellulose/tannic acid composite with antibacterial and anti-biofilm activities for biomedical applications

Biofilm-associated infections are in a high rate of recurrence and biofilms show formidable resistance to current antibiotics, making them a growing challenge in biomedical field. In this study, a biocompatible composite was developed by incorporating tannic acid (TA) and MgCl₂ to bacterial cellulose (BC) for antimicrobial and anti-biofilm purposes. The morphology was investigated by scanning electron microscopy (SEM), and chemical structure were characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectra (XPS). In vitro release profiles of tannic acid revealed that the Mg²⁺ cross-links help impede the release of TA from BC matrix, while composite BC-TA lacked Mg²⁺ ionic cross-links, thus more TA was released from the hydrogel. The BC-TA-Mg composites also displayed strong antibacterial activity against S. aureus, E. coli and P. aeruginosa. Moreover, the composites significantly reduced biofilm formation of S. aureus and P. aeruginosa after 24 h incubation by ∼80% and ∼87%, respectively. As a consequence, the BC-TA-Mg composites are a very promising material for combating biofilm-associated infections in biomedical and public health fields.

Antimicrobial Properties of Magnesium Open Opportunities to Develop Healthier Food

Magnesium is a vital mineral that takes part in hundreds of enzymatic reactions in the human body. In the past several years, new information emerged in regard to the antibacterial effect of magnesium. Here we elaborate on the recent knowledge of its antibacterial effect with emphasis on its ability to impair bacterial adherence and formation complex community of bacterial cells called biofilm. We further talk about its ability to impair biofilm formation in milk that provides opportunity for developing safer and qualitative dairy products. Finally, we describe the pronounced advantages of enrichment of food with magnesium ions, which result in healthier and more efficient food products.

Function of pYV Plasmid on Biofilm Formation of Yersinia enterocolitica ERL032123 in the Presence of Ca2

The effect of the virulence plasmid pYV and calcium ions on biofilm of Yersinia enterocolitica biofilm formation was determined using a microtiter plate assay. Loss of the pYV plasmid prevented biofilm formation and the presence of Ca²⁺ enhanced biofilm formation in cultures containing the pYV plasmid. Scanning electron microscopy supported the result from the microtiter plate assay showing that in the presence of Ca²⁺, the wild-type Y. enterocolitica strain formed a strong biofilm on a polycarbonate surface. The results implied that Ca²⁺ promotes Y. enterocolitica biofilm formation through the function of the pYV plasmid.

Calcium ion- and rhamnolipid-mediated deposition of soluble matters on biocarriers

Start-up of biofilm process initiated by the deposition of soluble matters on biocarriers is a very important yet time-consuming procedure. However, rapid start-up methods especially in the enhancement of soluble matters deposition have been rarely addressed. In this study, a quartz crystal microbalance with dissipation monitoring (QCM-D) was applied to investigate the influences of calcium ion and rhamnolipid (RL) on the deposition of soluble matters from real and synthetic industrial wastewaters with different configurations of organics (bovine serum albumin and sodium alginate) and ionic strength on the model biocarriers polystyrene and polyamide. Results showed that deposition was effectively promoted by the addition of Ca²⁺ and along with the increase in Ca²⁺ content. However, RL enhanced the deposition effectively only in hyperhaline wastewater through breaking hydration repulsion and decreased the deposition in low-salinity wastewater, and its influence to the deposited layer property exhibited characteristics of negative feedback. The combined use of Ca²⁺ and RL had a better enhancement effect than that of separate use and the mechanism involved can not be soundly explained only by Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The strategy of mediating the deposition of soluble matters on different biocarriers by adding Ca²⁺ and RL has important implications for regulating biofilm formation to accelerate the start-up process in attached-growth bioreactors.

Current therapies in treatment and prevention of fracture wound biofilms: why a multifaceted approach is essential for resolving persistent infections

Traumatic orthopedic injuries, particularly extremity wounds, are a significant cause of morbidity. Despite prophylactic antibiotic treatment and surgical intervention, persistent infectious complications can and do occur. Persistent bacterial infections are often caused by biofilms, communities of antibiotic tolerant bacteria encased within a matrix. The structural and metabolic differences in this mode of growth make treatment difficult. Herein, we describe both established and novel, experimental treatments targeted at various stages of wound healing that are specifically aimed at reducing and eliminating biofilm bacteria. Importantly, the highly tolerant nature of these bacterial communities suggests that most singular approaches could be circumvented and a multifaceted, combinatorial approach will be the most effective strategy for treating these complicated infections.

Extracellular polymeric substances, a key element in understanding biofilm phenotype

One of the key elements in the establishment and maintenance of the biofilm structure and properties is the extracellular matrix. The extracellular matrix is composed of water and extracellular polymeric substances (EPS): primarily polysaccharides, proteins and DNA. Characterization of the matrix requires component identification, as well as determination of the relative concentration of EPS constituents, including their physicochemical properties and descriptions of their interactions. Several types of experimental approaches with varying degrees of destructiveness can be utilized for this characterization. The analysis of biofilm by infrared spectroscopy gives information about the chemical content of the matrix and the proportions of different EPS. The sensitivity of a biofilm to hydrolytic enzymes targeting different EPS gives insight into the composition of the matrix and the involvement of matrix components in the integrity of the structure. Using both chemical and physical treatments, extraction and purification of EPS from the biofilm also provides a means of determining matrix composition. Purified and/or artificial EPS can be used to obtain artificial matrices and to study their properties. Using examples from the literature, this review will illustrate selected technologies useful in the study of EPS that provide a better understanding of the structure-function relationships in extracellular matrix, and thus the structure-function relationships of the biofilm phenotype.

Magnesium ions mitigate biofilm formation of Bacillus species via downregulation of matrix genes expression

The objective of this study was to investigate the effect of Mg(2+) ions on biofilm formation by Bacillus species, which are considered as problematic microorganisms in the food industry. We found that magnesium ions are capable to inhibit significantly biofilm formation of Bacillus species at 50 mM concentration and higher. We further report that Mg(2+) ions don't inhibit bacterial growth at elevated concentrations; hence, the mode of action of Mg(2+) ions is apparently specific to inhibition of biofilm formation. Biofilm formation depends on the synthesis of extracellular matrix, whose production in Bacillus subtilis is specified by two major operons: the epsA-O and tapA operons. We analyzed the effect of Mg(2+) ions on matrix gene expression using transcriptional fusions of the promoters for eps and tapA to the gene encoding β galactosidase. The expression of the two matrix operons was reduced drastically in response to Mg(2+) ions suggesting about their inhibitory effect on expression of the matrix genes in B. subtilis. Since the matrix gene expression is tightly controlled by Spo0A dependent pathway, we conclude that Mg(2+) ions could affect the signal transduction for biofilm formation through this pathway.

Changes in Sodium, Calcium, and Magnesium Ion Concentrations That Inhibit Geobacillus Biofilms Have No Effect on Anoxybacillus flavithermus Biofilms

This study investigated the effects of varied sodium, calcium, and magnesium concentrations in specialty milk formulations on biofilm formation by Geobacillus spp. and Anoxybacillus flavithermus. The numbers of attached viable cells (log CFU per square centimeter) after 6 to 18 h of biofilm formation by three dairy-derived strains of Geobacillus and three dairy-derived strains of A. flavithermus were compared in two commercial milk formulations. Milk formulation B had relatively high sodium and low calcium and magnesium concentrations compared with those of milk formulation A, but the two formulations had comparable fat, protein, and lactose concentrations. Biofilm formation by the three Geobacillus isolates was up to 4 log CFU cm(-2) lower in milk formulation B than in milk formulation A after 6 to 18 h, and the difference was often significant (P ≤ 0.05). However, no significant differences (P ≤ 0.05) were found when biofilm formations by the three A. flavithermus isolates were compared in milk formulations A and B. Supplementation of milk formulation A with 100 mM NaCl significantly decreased (P ≤ 0.05) Geobacillus biofilm formation after 6 to 10 h. Furthermore, supplementation of milk formulation B with 2 mM CaCl2 or 2 mM MgCl2 significantly increased (P ≤ 0.05) Geobacillus biofilm formation after 10 to 18 h. It was concluded that relatively high free Na(+) and low free Ca(2+) and Mg(2+) concentrations in milk formulations are collectively required to inhibit biofilm formation by Geobacillus spp., whereas biofilm formation by A. flavithermus is not impacted by typical cation concentration differences of milk formulations.

Proteomic profile of dormancy within Staphylococcus epidermidis biofilms using iTRAQ and label-free strategies

Staphylococcus epidermidis is an important nosocomial bacterium among carriers of indwelling medical devices, since it has a strong ability to form biofilms. The presence of dormant bacteria within a biofilm is one of the factors that contribute to biofilm antibiotic tolerance and immune evasion. Here, we provide a detailed characterization of the quantitative proteomic profile of S. epidermidis biofilms with different proportions of dormant bacteria. A total of 427 and 409 proteins were identified by label-free and label-based quantitative methodologies, respectively. From these, 29 proteins were found to be differentially expressed between S. epidermidis biofilms with prevented and induced dormancy. Proteins overexpressed in S. epidermidis with prevented dormancy were associated with ribosome synthesis pathway, which reflects the metabolic state of dormant bacteria. In the opposite, underexpressed proteins were related to catalytic activity and ion binding, with involvement in purine, arginine, and proline metabolism. Additionally, GTPase activity seems to be enhanced in S. epidermidis biofilm with induced dormancy. The role of magnesium in dormancy modulation was further investigated with bioinformatics tool based in predicted interactions. The main molecular function of proteins, which strongly interact with magnesium, was nucleic acid binding. Different proteomic strategies allowed to obtain similar results and evidenced that prevented dormancy led to an expression of a markedly different repertoire of proteins in comparison to the one of dormant biofilms.

A refined technique for extraction of extracellular matrices from bacterial biofilms and its applicability

Biofilm-forming bacteria embedded in polymeric extracellular matrices (ECMs) that consist of polysaccharides, proteins and/or extracellular DNAs (eDNAs) acquire high resistance to antimicrobial agents and host immune systems. To understand molecular mechanisms of biofilm formation and maintenance and to develop therapeutic countermeasures against chronic biofilm-associated infections, reliable methods to isolate ECMs are inevitable. In this study, we refined the ECM extraction method recently reported and evaluated its applicability. Using three Staphylococcus aureus biofilms in which proteins, polysaccharides or eDNAs are major contributors to their integrity, ECMs were extracted using salts and detergents. We found that extraction with 1.5 M sodium chloride (NaCl) could be optimum for not only ECM proteins but also polysaccharides and eDNAs. In addition, long-time incubation was not necessary for efficient ECM isolation. Lithium chloride (LiCl) was comparative to NaCl but is more expensive. In contrast to SDS, NaCl hardly caused leakage of intracellular proteins and did not affect viability of bacterial cells within biofilms. Furthermore, this method is applicable to other bacteria such as Gram-positive Staphylococcus epidermidis and Gram-negative Escherichia coli and Pseudomonas aeruginosa. Thus, this refined method is very simple, rapid, low cost and non-invasive and could be used for a broad range of applications.

Staphylococcal biofilm formation as affected by type acidulant

Staphylococcal growth and biofilm formation in culture medium where pH was lowered with weak organic (acetic and lactic) or strong inorganic (hydrochloric) acids were studied. The effects were evaluated by biomass measurements, cell-surface hydrophobicity, scanning electron microscopy (SEM), and confocal laser scanning microscopy (CLSM). The results demonstrated that the inhibition was related to type of acidulant and pH value. At pH 5.0, the antibacterial effect was more pronounced in the presence of acetic acid (58-60% growth reduction) compared with that in the presence of lactic (7-16% growth reduction) and hydrochloric acids (23-24% reduction). The biofilm biomass of Staphylococcus aureus and Staphylococcus epidermidis was reduced by 92, 85, 63, and 93, 87, 81% after exposition to acetic, lactic, and hydrochloric acids, respectively. Increasing the pH from 5.0 to 6.0 resulted in a noticeable reduction in the effectiveness of acids. A minor cells hydrophobic character was also documented. The SEM and CLSM revealed a poorly structured and thinner biofilm compared with the dense and multilayered control. Acidic environment could have important implications for food-processing system to prevent bacterial colonization and control biofilm formation. The findings of this study lead to consider the rational use of the type of acid to achieve acidic environments.

Inhibition by EGTA of the formation of a biofilm by clinical strains of Staphylococcus aureus

The effect of EGTA on the adhesion and on the formation of a biofilm by two reference and eight clinical strains of Staphylococcus aureus was studied. All the clinical strains were isolated from patients from Kinshasa. Spa typing confirmed that these clinical strains were distinct. The Biofilm Ring Test (BFRT®) showed that EGTA (100 µM-10 mM) inhibited the adhesion of the four clinical methicillin-resistant (MRSA) strains and the crystal violet staining method that it inhibited the formation of a biofilm by all the strains. Divalent cations abolished the effect of EGTA on the formation of a biofilm, specially in the clinical MRSA strains. EGTA had no effect on established biofilms. Only concentrations of EGTA higher than 10 mM were toxic to eukaryotic cells. Our results establish the effectiveness and the safety of lock solutions with EGTA to prevent the formation in vitro of biofilms by S. aureus.

Impact of food-related environmental factors on the adherence and biofilm formation of natural Staphylococcus aureus isolates

Staphylococcus aureus is a pathogenic bacterium capable of developing biofilms on food-processing surfaces, a pathway leading to cross contamination of foods. The purpose of this study was to investigate the influence of environmental stress factors found during seafood production on the adhesion and biofilm-forming properties of S. aureus. Adhesion and biofilm assays were performed on 26 S. aureus isolated from seafood and two S. aureus reference strains (ATCC 6538 and ATCC 43300). Cell surface properties were evaluated by affinity measurements to solvents in a partitioning test, while adhesion and biofilm assays were performed in polystyrene microplates under different stress conditions of temperature, osmolarity, and nutrient content. The expression of genes implicated in the regulation of biofilm formation (icaA, rbf and σ( B )) was analyzed by reverse transcription and quantitative real time PCR. In general, S. aureus isolates showed moderate hydrophobic properties and a marked Lewis-base character. Initial adhesion to polystyrene was positively correlated with the ionic strength of the growth medium. Most of the strains had a higher biofilm production at 37 °C than at 25 °C, promoted by the addition of glucose, whereas NaCl and MgCl(2) had a lower impact markedly affected by incubation temperatures. Principal Component Analysis revealed a considerable variability in adhesion and biofilm-forming properties between S. aureus isolates. Transcriptional analysis also indicated variations in gene expression between three characteristic isolates under different environmental conditions. These results suggested that the prevalence of S. aureus strains on food-processing surfaces is above all conditioned by the ability to adapt to the environmental stress conditions present during food production. These findings are relevant for food safety and may be of importance when choosing the safest environmental conditions and material during processing, packaging, and storage of seafood products.

Potential of calcium to scaffold an endodontic biofilm, thus protecting the micro-organisms from disinfection

Biofilms in the root canal of a tooth (endodontic biofilm) can induce and sustain apical periodontitis which is an oral inflammatory disease. Still, little is known about the composition of the endodontic biofilm. Studies on biofilms in root canals focus on the identification of the microbial species, but the majority of the biofilm consists of matrix material. Environmental aspects determine the structure of the biofilm and extracellular matrix. Calcium is involved in biofilm formation and activity at three levels. Firstly in cell-environment; calcium may 'condition' the surfaces of support and bacterial cells. Secondly, in cell-cell interaction; calcium plays a role in build up of biofilm structures. Typically, calcium ions act as 'cation bridges' between polysaccharides originating from different cells. Thirdly, within cells, calcium is required for certain biochemical reactions in bacteria and some bacterial physiological activities. Because calcium is present in the root canal, it could play a significant role in the organization of the biofilm. Chelators, already used in endodontics to remove the smear layer by disintegration of the structural cohesion calcium bonds, could weaken the biofilm matrix by removing calcium from the extracellular matrix thus disturbing its coherence. Subsequently, this disruption could increase the efficacy of disinfecting agents.

Chelating agents exert distinct effects on biofilm formation in Staphylococcus aureus depending on strain background: role for clumping factor B

Staphylococcus aureus is a leading cause of catheter infections, and biofilm formation plays a key role in the pathogenesis. Metal ion chelators inhibit bacterial biofilm formation and viability, making them attractive candidates as components in catheter lock solutions. The goal of this study was to characterize further the effect of chelators on biofilm formation. The effect of the calcium chelators ethylene glycol tetraacetic acid (EGTA) and trisodium citrate (TSC) on biofilm formation by 30 S. aureus strains was tested. The response to subinhibitory doses of EGTA and TSC varied dramatically depending on strain variation. In some strains, the chelators prevented biofilm formation, in others they had no effect, and they actually enhanced biofilm formation in others. The molecular basis for this phenotypic variability was investigated using two related strains: Newman, in which biofilm formation was inhibited by chelators, and 10833, which formed strong biofilms in the presence of chelators. It was found that deletion of the gene encoding the surface adhesin clumping factor B (clfB) completely eliminated chelator-induced biofilm formation in strain 10833. The role of ClfB in biofilm formation activity in chelators was confirmed in additional strains. It was concluded that biofilm-forming ability varies strikingly depending on strain background, and that ClfB is involved in biofilm formation in the presence EGTA and citrate. These results suggest that subinhibitory doses of chelating agents in catheter lock solutions may actually augment biofilm formation in certain strains of S. aureus, and emphasize the importance of using these agents appropriately so that inhibitory doses are achieved consistently.

Effect of alkaline pH on staphylococcal biofilm formation

Biofilms are a serious problem, cause of severe inconvenience in the biomedical, food and industrial environment. Staphylococcus aureus and S. epidermidis are important pathogenic bacteria able to form thick and resistant biofilms on various surfaces. Therefore, strategies aimed at preventing or at least interfering with the initial adhesion and subsequent biofilm formation are a considerable achievement. The aim of this study was to evaluate the effect of alkaline pH on bacterial adhesion and further biofilm formation of S. aureus and S. epidermidis strains by biofilm biomass, cell-surface hydrophobicity, scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) analysis. The results demonstrated that the amount of biofilm biomass formed and the surface hydrophobicity were significantly less than what were observed at higher levels of pH. SEM and CLSM images revealed a poorly structured and very thin biofilm (2.5-3 times thinner than that of the controls). The inhibiting effect of the alkaline pH on the bacterial attachment impaired the normal development of biofilm that arrested at the microcolony stage. Alkaline formulations could be promising towards the control of bacterial colonization and therefore the reduction of the biofilm-related hazard. In the clinical setting, alkaline solutions or cleaners could be promising to prevent the bacterial colonization, by treating surfaces such as catheters or indwelling medical devices, reducing the risk of biofilm related infections.

Nutrients determine the spatial architecture of Paracoccus sp. biofilm

Bacterial biofilms adapt and shape their structure in response to varied environmental conditions. A statistical methodology was adopted in this study to empirically investigate the influence of nutrients on biofilm structural parameters deduced from confocal scanning laser microscope images of Paracoccus sp.W1b, a denitrifying bacterium. High concentrations of succinate, Mg(++), Ca(++), and Mn(++) were shown to enhance biofilm formation whereas higher concentration of iron decreased biofilm formation. Biofilm formed at high succinate was uneven with high surface to biovolume ratio. Higher Mg(++) or Ca(++) concentrations induced cohesion of biofilm cells, but contrasting biofilm architectures were detected. Biofilm with subpopulation of pillar-like protruding cells was distributed on a mosaic form of monolayer cells in medium with 10 mM Mg(++). 10 mM Ca(++) induced a dense confluent biofilm. Denitrification activity was significantly increased in the Mg(++)- and Ca(++)-induced biofilms. Chelator treatment of various biofilm ages indicated that divalent cations are important in the initial stages of biofilm formation.

Control of microbial contamination in dental unit water systems using tetra-sodium EDTA

AIM

To examine the efficacy of tetra-sodium EDTA in controlling microbial contamination of dental unit water systems (DUWS).

METHODS AND RESULTS

Ten dental units were treated once a week with either 4% or 8% tetra-sodium EDTA for four or two consecutive weeks, respectively. Before treatment, 43% and 60% of the water samples from the air/water triple syringe and high-speed hand-pieces, respectively, exceeded the American Dental Association (ADA) guidelines of 200 CFU ml(-1) water during a 6-week baseline period. After each weekend treatment, the levels of microbial contamination in all DUWS fell significantly (P < 0.001) to below the ADA guideline. By the end of the week, microbial counts in the outflowing water had returned to baseline levels indicating a transient effect of single doses of tetra-sodium EDTA, and the need for multiple applications. The biofilms were virtually eliminated after a single weekend treatment.

CONCLUSIONS

Tetra-sodium EDTA is effective in controlling microbial contamination in DUWS.

SIGNIFICANCE AND IMPACT OF THE STUDY

Inexpensive, effective and safe products for reducing the microbial load of water from DUWS are needed to meet ADA and other national guidelines. Tetra-sodium EDTA can significantly reduce microbial biofilms and bacterial counts in outflowing water, and is compatible for use in DUWS.

Activity of novel antibiotic lock solutions in a model against isolates of catheter-related bloodstream infections

BACKGROUND

Catheter-related bloodstream infections (CRBSIs) are a primary concern in patients with indwelling central venous catheters (CVCs). Instillation of an antibiotic lock solution may serve as an adjunctive therapy.

OBJECTIVE

To evaluate the efficacy of novel antibiotic-anticoagulant lock solutions using an in vitro model of CVC infection.

METHODS

The following lock solutions were evaluated: daptomycin 1 mg/mL (reconstituted with lactated Ringer's [LR]) plus heparin 5000 units/mL, tigecycline 0.5 mg/mL plus ethylenediaminetetraacetate (EDTA) 30 mg/mL, gentamicin 5 mg/mL plus EDTA 30 mg/mL, cefazolin 5 mg/mL plus heparin 5000 units/mL, and phosphate-buffered NaCl 0.9% as the control solution. Analysis was performed on Hickman catheter segments inoculated with the following organisms: methicillin-sensitive Staphylococcus aureus, methicillin-resistant S. aureus (MRSA), Staphylococcus epidermidis, and Pseudomonas aeruginosa. The catheters were incubated in the candidate lock solutions for 0, 2, 4, and 24 hours. Student's t-tests were conducted to evaluate reduction in log(10) colony-forming units/milliliter (cfu/mL) of individual lock solutions compared with the control solution. For each organism, analysis of variance and Student's t-tests were performed to determine whether differences existed among the lock solutions.

RESULTS

Gentamicin plus EDTA (G+EDTA) and tigecycline plus EDTA (Ti+EDTA) resulted in significant reductions (p < 0.05) of log(10) cfu/mL at 24 hours for all organisms tested. Daptomycin, reconstituted in LR, plus heparin (D+LR+H) demonstrated potent activity against all staphylococcal species (p < 0.05). With respect to MRSA, G+EDTA displayed significantly better activity than Ti+EDTA and cefazolin plus heparin (p < 0.05), but there was no significant difference compared with D+LR+H. No antagonism was noted with the addition of anticoagulants to the solutions.

CONCLUSIONS

Gentamicin, tigecycline, and daptomycin in combination with anticoagulants as lock solutions displayed potent activity against common pathogens responsible for CRBSIs. Each of these lock solutions deserves strong consideration for study in a clinical trial. Further data on compatibility and stability of these solutions are needed before routine clinical use can be recommended.

The role of chelators in preventing biofilm formation and catheter-related bloodstream infections

PURPOSE OF REVIEW

As metallic cations are essential to microbial adherence, biofilm formation, and bacterial growth, efforts have been directed toward utilizing metal-binding chelators that have the capability of inhibiting bacterial growth by disrupting surface adherence and preventing biofilm production. This review focuses on recent advances in the role of chelators in biofilm disruption and prevention of catheter-related bloodstream infections.

RECENT FINDINGS

The most important factor in the pathogenesis of catheter-related bloodstream infections is the intraluminal colonization of the central venous catheters through the formation of bacterial biofilm matrix in which microbial organisms embed themselves and eventually become a source of catheter-related bloodstream infections. It has been demonstrated that high-affinity metal-binding chelators including ethylenediamine-tetraacetic acid and citrate have the capacity of inhibiting microbial growth by disrupting surface adherence and preventing biofilm production. Furthermore, ethylenediamine-tetraacetic acid and citrate have been clinically shown to be highly effective and outperform heparin in the prevention and treatment of catheter-related bloodstream infections when used as a component of antimicrobial catheter lock solutions.

SUMMARY

It is suggested that the addition of chelators such as ethylenediamine-tetraacetic acid and citrate to antimicrobial lock solutions provides an innovative and superior alternative to heparin lock solution in the prevention and treatment of catheter-related bloodstream infections.

Influence of magnesium ions on biofilm formation by Pseudomonas fluorescens

Mg(2+) can potentially influence bacterial adhesion directly through effects on electrostatic interactions and indirectly by affecting physiology-dependent attachment processes. However, the effects of Mg(2+) on biofilm structure are largely unknown. In this study, Pseudomonas fluorescens was used to investigate the influence of Mg(2+) concentration (0, 0.1 and 1.0mM MgCl(2)) on biofilm growth. Planktonic and attached cells were enumerated (based on DAPI staining) while biofilm structures were examined via confocal laser scanning microscopy and three-dimensional structures were reconstructed. Mg(2+) concentration had no influence on growth of planktonic cells but, during biofilm formation, Mg(2+) increased the abundance of attached cells. For attached cells, the influence of Mg(2+) concentration changed over time, suggesting that the role of Mg(2+) in bacterial attachment is complex and dynamic. Biofilm structures were heterogeneous and surface colonization and depth increased with increasing Mg(2+) concentrations. Overall, for P. fluorescens, Mg(2+) increased initial attachment and altered subsequent biofilm formation and structure.

Catheter lock solutions influence staphylococcal biofilm formation on abiotic surfaces

BACKGROUND

Microbial biofilms form on central venous catheters and may be associated with systemic infections as well as decreased dialysis efficiency due to catheter thrombosis. The most widely used anticoagulant catheter lock solution in the US is sodium heparin. We have previously shown that sodium heparin in clinically relevant concentrations enhances Staphylococcus aureus biofilm formation. In the present study, we examine the effect of several alternative catheter lock solutions on in vitro biofilm formation by laboratory and clinical isolates of S. aureus and coagulase-negative staphylococci (CNS).

METHODS

Lepirudin, low molecular weight heparin, tissue plasminogen activator, sodium citrate, sodium citrate with gentamicin and sodium ethylene diamine tetra-acetic acid (EDTA) were assessed for their effect on biofilm formation on polystyrene, polyurethane and silicon elastomer.

RESULTS

Sodium citrate at concentrations above 0.5% efficiently inhibits biofilm formation and cell growth of S. aureus and Staphylococcus epidermidis. Subinhibitory concentrations of sodium citrate significantly stimulate biofilm formation in most tested S. aureus strains, but not in CNS strains. Sodium EDTA was effective in prevention of biofilm formation as was a combination of sodium citrate and gentamicin. Low molecular weight heparin stimulated biofilm formation of S. aureus, while lepirudin and tissue plasminogen activator had little effect on S. aureus biofilm formation.

CONCLUSIONS

This in vitro study demonstrates that heparin alternatives, sodium citrate and sodium EDTA, can prevent the formation of S. aureus biofilms, suggesting that they may reduce the risk of biofilm-associated complications in indwelling catheters. This finding suggests a biological mechanism for the observed improvement in catheter-related outcomes in recent clinical comparisons of heparin and trisodium citrate as catheter locking solutions. A novel and potential clinically relevant finding of the present study is the observation that citrate at low levels strongly stimulates biofilm formation by S. aureus.

BisEDT and RIP act in synergy to prevent graft infections by resistant staphylococci

Staphylococci are a major cause of infections associated with indwelling medical devices. Biofilm formation on these devices adds to the antibiotic resistance seen among clinical isolates. RNAIII-inhibiting peptide (RIP) is a heptapeptide that inhibits staphylococcal pathogenesis, including biofilm formation, by obstructing quorum sensing mechanisms. Bismuth ethanedithiol (BisEDT) also prevents biofilm formation at subinhibitory concentrations. RIP and BisEDT were combined to prevent infections in a rat graft model, using antibiotic sensitive and resistant strains of Staphylococcus aureus and Staphylococcus epidermidis. BisEDT, RIP, or rifampin, or their combinations reduced the graft associated bacterial load over seven days. BisEDT-RIP was the best combination, reducing bacterial load to undetectable levels. BisEDT-RIP may prove useful for coating medical devices to prevent staphylococcal infections.

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 biofilms: from the natural environment to infectious diseases

Biofilms--matrix-enclosed microbial accretions that adhere to biological or non-biological surfaces--represent a significant and incompletely understood mode of growth for bacteria. Biofilm formation appears early in the fossil record (approximately 3.25 billion years ago) and is common throughout a diverse range of organisms in both the Archaea and Bacteria lineages, including the 'living fossils' in the most deeply dividing branches of the phylogenetic tree. It is evident that biofilm formation is an ancient and integral component of the prokaryotic life cycle, and is a key factor for survival in diverse environments. Recent advances show that biofilms are structurally complex, dynamic systems with attributes of both primordial multicellular organisms and multifaceted ecosystems. Biofilm formation represents a protected mode of growth that allows cells to survive in hostile environments and also disperse to colonize new niches. The implications of these survival and propagative mechanisms in the context of both the natural environment and infectious diseases are discussed in this review.

The effects of magnesium, calcium and EDTA on slime production by Staphylococcus epidermidis strains

Effect of magnesium, calcium and EDTA on slime production by 15 slime-positive and 13 slime-negative Staphylococcus epidermidis strains isolated from various clinical specimens was determined. The slime production on tryptic soy broth was significantly enhanced after addition of 128 mumol/L Mg2+. Similarly, the addition of Ca2+ caused a significant increase in slime production of all tested strains when concentration of Ca2+ exceeded 64 mumol/L. In contrast, in the presence of EDTA the slime production by all strains was significantly reduced. Hence Ca2+ and Mg2+ increase slime production of S. epidermidis. This finding is important in the context of the pathogenesis of biomedical implant infections caused by S. epidermidis.

Bacterial adhesion: seen any good biofilms lately?

The process of surface adhesion and biofilm development is a survival strategy employed by virtually all bacteria and refined over millions of years. This process is designed to anchor microorganisms in a nutritionally advantageous environment and to permit their escape to greener pastures when essential growth factors have been exhausted. Bacterial attachment to a surface can be divided into several distinct phases, including primary and reversible adhesion, secondary and irreversible adhesion, and biofilm formation. Each of these phases is ultimately controlled by the expression of one or more gene products. Ultrastructurally, the mature bacterial biofilm resembles an underwater coral reef containing pyramidal or mushroom-shaped microcolonies of organisms embedded within an extracellular glycocalyx, with channels and cavities to allow the exchange of nutrients and waste. The biofilm protects its inhabitants from predators, dehydration, biocides, and other environmental extremes while regulating population growth and diversity through primitive cell signals. From a physiological standpoint, surface-bound bacteria behave quite differently from their planktonic counterparts. Recognizing that bacteria naturally occur as surface-bound and often polymicrobic communities, the practice of performing antimicrobial susceptibility tests using pure cultures and in a planktonic growth mode should be questioned. That this model does not reflect conditions found in nature might help explain the difficulties encountered in the management and treatment of biomedical implant infections.

Staphylococcus and biofilms

The genetic and molecular basis of biofilm formation in staphylococci is multifaceted. The ability to form a biofilm affords at least two properties: the adherence of cells to a surface and accumulation to form multilayered cell clusters. A trademark is the production of the slime substance PIA, a polysaccharide composed of beta-1,6-linked N-acetylglucosamines with partly deacetylated residues, in which the cells are embedded and protected against the host's immune defence and antibiotic treatment. Mutations in the corresponding biosynthesis genes (ica operon) lead to a pleiotropic phenotype; the cells are biofilm and haemagglutination negative, less virulent and less adhesive on hydrophilic surfaces. ica expression is modulated by various environmental conditions, appears to be controlled by SigB and can be turned on and off by insertion sequence (IS) elements. A number of biofilm-negative mutants have been isolated in which polysaccharide intercellular adhesin (PIA) production appears to be unaffected. Two of the characterized mutants are affected in the major autolysin (atlE) and in D-alanine esterification of teichoic acids (dltA). Proteins have been identified that are also involved in biofilm formation, such as the accumulation-associated protein (AAP), the clumping factor A (ClfA), the staphylococcal surface protein (SSP1) and the biofilm-associated protein (Bap). Concepts for the prevention of obstinate polymer-associated infections include the search for new anti-infectives active in biofilms and new biocompatible materials that complicate biofilm formation and the development of vaccines.

Study of the microbial aggregation in Mycobacterium using image analysis and electron microscopy

Cellular aggregation, which occurs in both prokaryotes and eukaryotes, is controlled by the hydrophobicity as well as the electrokinetic potential of the cell surface and substratum. It is known that the Mycobacterium genus form aggregates, but the influence of sugar on the cellular aggregation has not been reported for this genus. The mutant strain Mycobacterium sp. MB-3683 that transforms sterol to androstenedione (AD), a steroidal precursor used by the pharmaceutical industries, was employed in this study. This strain was cultivated in a synthetic medium on three sugars (glycerol, glucose and fructose) at different concentrations, and at 144 h microbial growth, cellular aggregation, hydrophobicity, lipid content, fatty acid composition, and width of cellular walls were measured. It was observed that at different sugar concentrations, similar growth and pH were obtained. However, in fructose, the aggregation level was significantly high, followed by glycerol and glucose (fructose < glycerol < glucose). These results were confirmed using electron microscopy and the aggregate area quantified by image analysis. Hydrophobicity was the highest in fructose and the lowest in glucose. The total lipids, in contrast to cellular hydrophobicity, were higher in glucose than glycerol. Although, the hydrophilic-lipophilic balance (HLB) of principal fatty acids isolated was similar regardless of sugar used. In glycerol and fructose, the paraffins were observed, which are responsible for the high cellular hydrophobicity detected above. The width of cell wall of the organisms grown on glucose and fructose was similar, but in glycerol the walls were very thin. There is a correspondence between cell wall width and lipid content.

Influence of calcium and other cations on surface adhesion of bacteria and diatoms: A review

Association with a surface is an important aspect of survival for microorganisms in natural and manmade environments/Both bacteria and diatoms are involved in such associations. In many cases, this leads to surface fouling, which often results in surface deterioration and mechanical failure in industrial systems. We now know that microorganisms exploit many strategies to establish associations with surfaces. As in the case of other cellular processes, calcium ions seem to play an important role in adhesion of cells to surfaces. Calcium is involved in non-specific interactions such as neutralization of the electrical double layer between cell and substratum surface as well as specific adhesive interactions that cannot be replaced by other cations. The unique properties of calcium ions promote both specific and non-specific interactions with protein and polysaccha-ride adhesin molecules at the cell surface. As important, but less well understood, calcium ions also influence the way microbial cells interact with different substrata.

Use of a modified Robbins device to directly compare the adhesion of Staphylococcus epidermidis RP62A to surfaces

Staphylococcus epidermidis is a frequent cause of infection associated with the use of biomedical devices. Flow cell studies of the interaction between bacteria and surfaces do not generally allow direct comparison of different materials using the same bacterial suspension. The use of a modified Robbins Device (MRD) to compare the adhesion to different surfaces of Staph. epidermidis RP62A grown in continuous culture was investigated. Adhesion to glass was compared with siliconized glass, plasma-conditioned glass, titanium, stainless steel and Teflon. Attachment to siliconized glass was also compared with glass under differing ionic strength, and divalent cation concentrations. Both the differences in numbers adhering and changes in adhesion (slope) through the MRD were compared. There was a trend towards higher numbers adhering to the discs at the in-flow end of the MRD than at the outflow end, probably reflecting depletion of adherent bacteria in the interacting stream. Adhesion of Staph. epidermidis RP62A to siliconized glass and Teflon was reduced when compared to glass with increasing flow rates. Adhesion to stainless steel was not affected by flow rate and titanium gave a different slope of adhesion through the MRD when compared with glass, suggesting an interaction with different sub-populations within the interacting stream. Differences between siliconized glass and glass at flow rates of 300 ml h-1 were abolished by the addition of calcium or EDTA and reduced by the addition of magnesium. Increasing ionic strength reduced the statistical significance of the differences between glass and siliconized glass. Pre-conditioning of glass with pooled human plasma reduced adhesion compared with untreated glass and again gave a different slope to glass. The MRD linked to a chemostat can be used to compare directly bacterial adhesion to potential biomaterials. Variable depletion of the interacting stream should be taken into account in the interpretation of results. Divalent cation concentration, substrate properties and flow rate were important determinants of the comparative adhesion of Staph. epidermidis RP62A to surfaces.

Quantitation of bacterial adhesion to polymer surfaces by bioluminescence

Quantitation of microbes adhering to a surface is commonly used in studies of microbial adhesion to different surfaces. We have quantified different staphylococcal strains adhering to polymer surfaces by measuring bacterial ATP (adenosine triphosphate) by bioluminescence. The method is sensitive, having a detection limit of 10(4) bacterial cells. Viable counting of bacterial cells may yield falsely low results due to the presence of "dormant" and adherent bacteria. By using bioluminescence, this can be avoided. Cells of different bacterial species and cells of strains of the same species were shown to differ significantly in their basal ATP content (8.7 x 10(-13) - 5.2 x 10(-22) MATP). The size of adherent and planktonic bacteria decreased with time (0.7 micron-->0.3 micron, 20 days). During incubation in nutrient-poor buffer ("starvation"), the ATP content of adherent bacteria decreased after 24-96 h whereas that of planktonic bacteria was stable over 20 days. The presence of human serum or plasma did not interfere significantly with the test results. Since the ATP concentration of bacterial strains of different species varies and is also influenced by the growth conditions of bacteria (solid or liquid culture medium), a species-specific standard curve has to be established for bacteria grown under the same culture conditions. We conclude that the method is a sensitive tool to quantify adherent bacteria during experiments lasting for less than 6 h and constitutes a valuable method to be used in conjunction with different microscopical techniques.

Investigation of calcium-binding sites on the surfaces of selected gram-positive oral organisms

Dental plaque is rich in anionic groups with a high calcium-binding capacity which may affect mineral dynamics at the tooth surface. The two major calcium-binding sites on Gram-positive cell surfaces are carboxylate groups (in proteins and peptidoglycan cross-links) and phosphate groups (in lipoteichoic and teichoic acid). Equilibrium dialysis was used to measure calcium-binding capacities of whole cells and purified cell-wall material (CWM) from Streptococcus mutans R9, Strep. oralis EF186, Strep. gordonii NCTC 7865, Strep. downei NCTC 11391, Actinomyces naeslundii WVU627 and Lactobacillus casei AC413. This material was stripped of phosphate (PS-CWM) and treated to mask carboxylate groups (CM-CWM). Whole-cell calcium-binding capacities ranged from 240 (Strep. downei) to 50 (L. casei) mu mol/g (dry wt). Differences in CWM, PS-CWM and CM-CWM calcium-binding capacities demonstrated the greater importance of phosphate in comparison with carboxylate groups in cell calcium binding. These data indicate that, in streptococci, calcium binding is predominantly phosphate group-based, especially in the teichoic acid-containing Strep. oralis. In the other species tested, calcium binding is predominantly carboxylate group-based.