Young Biofilms Research Articles

Real-Time Measurements of the Redox States of c-Type Cytochromes in Electroactive Biofilms: A Confocal Resonance Raman Microscopy Study

Confocal Resonance Raman Microscopy (CRRM) was used to probe variations of redox state of c-type cytochromes embedded in living mixed-culture electroactive biofilms exposed to different electrode polarizations, under potentiostatic and potentiodynamic conditions. In the absence of the metabolic substrate acetate, the redox state of cytochromes followed the application of reducing and oxidizing electrode potentials. Real-time monitoring of the redox state of cytochromes during cyclic voltammetry (CV) in a potential window where cytochromes reduction occurs, evidenced a measurable time delay between the oxidation of redox cofactors probed by CV at the electrode interface, and oxidation of distal cytochromes probed by CRRM. This delay was used to tentatively estimate the diffusivity of electrons through the biofilm. In the presence of acetate, the resonance Raman spectra of young (10 days, j = 208±49 µA cm−2) and mature (57 days, j = 267±73 µA cm−2) biofilms show that cytochromes remained oxidized homogeneously even at layers as far as 70 µm from the electrode, implying the existence of slow metabolic kinetics that do not result in the formation of a redox gradient inside the biofilm during anode respiration. However, old biofilms (80 days, j = 190±37 µA cm−2) with thickness above 100 µm were characterized by reduced catalytic activity compared to the previous developing stages. The cytochromes in these biofilm were mainly in the reduced redox state, showing that only aged mixed-culture biofilms accumulate electrons during anode respiration. These results differ substantially from recent observations in pure Geobacter sulfurreducens electroactive biofilms, in which accumulation of reduced cytochromes is already observed in thinner biofilms, thus suggesting different bottlenecks in current production for mixed-culture and G. sulfurreducens biofilms.

Artificial Klebsiella pneumoniae biofilm model mimicking in vivo system: altered morphological characteristics and antibiotic resistance

The purpose of this study was to develop a biofilm model of Klebsiella pneumoniae B5055, mimicking in vivo biofilm system so as to determine susceptibility of different phases of biofilm to antibiotics by three-dimensional analysis. Artificial mature biofilm of K. pneumoniae was made on black, polycarbonate membranes. Biofilm structure was visualized by scanning electron microscope (SEM) and confocal laser scanning microscopy (CLSM). Viable count method, CLSM and SEM analysis confirmed that mature, uniform and viable biofilms can be formed on the polycarbonate membranes by this method. The three-dimensional heterogeneity of biofilm was confirmed on the basis of results of CLSM, which is an important characteristics of in vivo biofilm system. Staining with the LIVE/DEAD BacLight viability kit and acridine orange suggested that the center of biofilm had more inactive cells compared with actively dividing cells on the periphery. Amikacin at a concentration of 40 μg ml⁻¹ was effective against younger biofilm whereas ineffective against older biofilm that showed sparsely populated dead cells using the BacLight viability staining kit. Role of altered morphological characteristics toward increased antibiotic susceptibility was also studied for different phases of K. pneumoniae biofilm by CLSM and light microscopy. Thickness of biofilm increased from 0.093 to 0.231 mm with time. So, both heterogeneity and thickness of the biofilm are likely to influence the ineffectiveness of amikacin in older biofilm. The present model holds considerable clinical relevance and may be useful for evaluating the efficacy of antimicrobial agent on bacterial biofilms in vitro.

Effect of Long-term Exposure to Endodontic Disinfecting Solutions on Young and Old Enterococcus faecalis Biofilms in Dentin Canals

IntroductionThe purpose of this study was to evaluate the antimicrobial activity on Enterococcus faecalis biofilms in dentin canals of short-term and long-term exposure to different endodontic disinfecting solutions by using a dentin infection model and confocal laser scanning microscopy. MethodsDentinal tubules in semi-cylindrical dentin blocks were filled with E. faecalis by centrifugation and incubated to form 1-day-old and 3-week-old biofilms. The young and mature biofilms in dentin were subjected to sterile water, 2% chlorhexidine, 2% sodium hypochlorite (NaOCl), and 6% NaOCl for 3, 10, and 30 minutes. After treatments, the proportion of bacteria killed by the disinfectants was analyzed by confocal laser scanning microscopy by using LIVE/DEAD bacterial viability stain. ResultsThe proportion of killed bacteria was lower after 3 minutes than after 10 and 30 minutes of exposure to the disinfecting agents (P < .05). The killing of bacteria in the E. faecalis biofilms was fastest during the first 3 minutes and slowed down greatly after 10 minutes. Six percent NaOCl was the most effective antibacterial solution against both the 1-day-old and 3-week-old biofilms (P < .05). No significant difference in bacterial killing was detected between 2% chlorhexidine and 2% NaOCl (P > .05). Significantly more cells were killed in young biofilms than in old biofilms in all groups (P < .05). ConclusionsThe killing of bacteria in infected dentin by disinfecting solutions is time-dependent. However, little additional killing is obtained after the first 10 minutes of exposure.

Antibiotic Activity against Naive and Induced Streptococcus pneumoniae Biofilms in an In Vitro Pharmacodynamic Model

Biofilms play a role in the pathogenicity of pneumococcal infections. A pharmacodynamic in vitro model of biofilm was developed that allows characterization of the activity of antibiotics against viability and biomass by using in parallel capsulated (ATCC 49619) and noncapsulated (R6) reference strains. Naive biofilms were obtained by incubating fresh planktonic cultures for 2 to 11 days in 96-well polystyrene plates. Induced biofilms were obtained using planktonic bacteria collected from the supernatant of 6-day-old naive biofilms. Biomass production was more rapid and intense in the induced model, but the levels were similar for both strains. Full concentration responses fitting sigmoidal regressions allowed calculation of maximal efficacies and relative potencies of drugs. All antibiotics tested (amoxicillin, clarithromycin, solithromycin, levofloxacin, and moxifloxacin) were more effective against young naive biofilms than against old or induced biofilms, except macrolides/ketolides, which were as effective at reducing viability in 2-day-old naive biofilms and in 11-day-old induced biofilms of R6. Macrolides/ketolides, however, were less potent than fluoroquinolones against R6 (approximately 5- to 20-fold-higher concentrations needed to reduction viability of 20%). However, at concentrations obtainable in epithelial lining fluid, the viabilities of mature or induced biofilms were reduced 15 to 45% (amoxicillin), 17 to 44% (macrolides/ketolides), and 12 to 64% (fluoroquinolones), and biomasses were reduced 5 to 45% (amoxicillin), 5 to 60% (macrolides/ketolides), and 10 to 76% (fluoroquinolones), with solithromycin and moxifloxacin being the most effective and the most potent agents (due to lower MICs) in their respective classes. This study allowed the ranking of antibiotics with respect to their potential effectiveness in biofilm-related infections, underlining the need to search for still more effective options.

Antimicrobial Efficacy of Photodynamic Therapy and Sodium Hypochlorite on Monoculture Biofilms of Enterococcus faecalis at Different Stages of Development

As the Enterococcus faecalis biofilm ages, it is likely that bacteria in mature and old biofilms will become more resistant to commonly used antibacterial irrigants. Photodynamic therapy (PDT) has been used to kill resistant bacteria organized in a biofilm. This study aimed to investigate the antimicrobial effectiveness of 1% sodium hypochlorite (NaOCl), 2.5% NaOCl, and PDT on E. faecalis biofilm at different stages of development. In this study 4-, 6-, and 8-week-old E. faecalis biofilms were subjected to one of the following approaches: phosphate-buffered saline solution (PBS), PDT, or 1% and 2.5% NaOCl. Dentin chip suspensions were used for colony forming units (CFU) counting to estimate remaining E. faecalis counts. PDT and 2.5% NaOCl completely eliminated E. faecalis biofilms in three stages of biofilm development, whereas 1% NaOCl resulted in 81.88%, 85.73%, and 78.62% reductions of bacterial counts in 4-, 6-, and 8-week-old biofilms, respectively, which was significantly more than PBS. The bacteria in mature and old biofilms were more resistant to 1% NaOCl than were the bacteria in young biofilms. Overall survival and residual bacteria increase with biofilm aging. PDT and the 2.5% NaOCl solution were equally efficient in completely eliminating E. faecalis biofilms at all three stages.

Removal of nitrogen by Algal Turf Scrubber Technology in recirculating aquaculture system

Ongoing research in recirculation aquaculture focuses on evaluating and improving the purification potential of different types of filters. Algal Turf Scrubber (ATS) are special as they combine sedimentation and biofiltration. An ATS was subjected to high nutrient loads of catfish effluent to examine the effect of total suspended solids (TSS), sludge accumulation and nutrient loading rate on total ammonia nitrogen (TAN), nitrite and nitrate removal. Nutrient removal rates were not affected at TSS concentration of up to 0.08 g L−1 (P > 0.05). TAN removal rate was higher (0.656 ± 0.088 g m−² day−1 TAN) in young biofilm than (0.302 ± 0.098 g m−² day−1 TAN) in mature biofilm at loading rates of 3.81 and 3.76 g m−² day−1 TAN (P < 0.05), respectively, which were considered close to maximum loading. TAN removal increased with TAN loading, which increased with hydraulic loading rate. There was no significant difference in removal rate for both nitrite and nitrate between young and mature biofilms (P > 0.05). The ATS ably removed nitrogen at high rates from catfish effluent at high loading rates. ATS-based nitrogen removal exhibits high potential for use with high feed loads in intensive aquaculture.

Successional development of biofilms in moving bed biofilm reactor (MBBR) systems treating municipal wastewater

Biofilm-based technologies, such as moving bed biofilm reactor (MBBR) systems, are widely used to treat wastewater. Biofilm development is important for MBBR systems as much of the microbial biomass is retained within reactors as biofilm on suspended carriers. Little is known about this process of biofilm development and the microorganisms upon which MBBRs rely. We documented successional changes in microbial communities as biofilms established in two full-scale MBBR systems treating municipal wastewater over two seasons. 16S rRNA gene-targeted pyrosequencing and clone libraries were used to describe microbial communities. These data indicate a successional process that commences with the establishment of an aerobic community dominated by Gammaproteobacteria (up to 52 % of sequences). Over time, this community shifts towards dominance by putatively anaerobic organisms including Deltaproteobacteria and Clostridiales. Significant differences were observed between the two wastewater treatment plants (WWTPs), mostly due to a large number of sequences (up to 55 %) representing Epsilonproteobacteria (mostly Arcobacter) at one site. Archaea in young biofilms included several lineages of Euryarchaeota and Crenarchaeota. In contrast, the mature biofilm consisted entirely of Methanosarcinaceae (Euryarchaeota). This study provides new insights into the community structure of developing biofilms at full-scale WWTPs and provides the basis for optimizing MBBR start-up and operational parameters.

A Combined Pharmacodynamic Quantitative and Qualitative Model Reveals the Potent Activity of Daptomycin and Delafloxacin against Staphylococcus aureus Biofilms

Biofilms are associated with persistence of Staphylococcus aureus infections and therapeutic failures. Our aim was to set up a pharmacodynamic model comparing antibiotic activities against biofilms and examining in parallel their effects on viability and biofilm mass. Biofilms of S. aureus ATCC 25923 (methicillin-sensitive S. aureus [MSSA]) or ATCC 33591 (methicillin-resistant S. aureus [MRSA]) were obtained by culture in 96-well plates for 6 h/24 h. Antibiotic activities were assessed after 24/48 h of exposure to concentrations ranging from 0.5 to 512 times the MIC. Biofilm mass and bacterial viability were quantified using crystal violet and the redox indicator resazurin. Biofilms stained with Live/Dead probes were observed by using confocal microscopy. Concentration-effect curves fitted sigmoidal regressions, with a 50% reduction toward both matrix and viability obtained at sub-MIC or low multiples of MICs against young biofilms for all antibiotics tested. Against mature biofilms, maximal efficacies and potencies were reduced, with none of the antibiotics being able to completely destroy the matrix. Delafloxacin and daptomycin were the most potent, reducing viability by more than 50% at clinically achievable concentrations against both strains, as well as reducing biofilm depth, as observed in confocal microscopy. Rifampin, tigecycline, and moxifloxacin were effective against mature MRSA biofilms, while oxacillin demonstrated activity against MSSA. Fusidic acid, vancomycin, and linezolid were less potent overall. Antibiotic activity depends on biofilm maturity and bacterial strain. The pharmacodynamic model developed allows ranking of antibiotics with respect to efficacy and potency at clinically achievable concentrations and highlights the potential utility of daptomycin and delafloxacin for the treatment of biofilm-related infections.

수도관 재질에 형성된 초기 생물막 형성 미생물의 군집 특성

Annular Biofilm Reactor (ABR) equipped with coupons of three different pipe materials (STS 304, PVC, PE) was used to generate drinking water biofilm samples. The level of assimilable organic carbon (AOC) during the sample generation period was <TEX>$37.3{\mu}g/L$</TEX>, and this level did not seem to be low enough to limit the formation of biofilm in this study. Terminal-restriction fragment length polymorphism (T-RFLP) analyses determined T-RF profile as early as 3 h of exposure on PVC coupons. Average surface roughness (<TEX>$R_a$</TEX>) measured by atomic force microscopic analyses was 125.7 nm for PVC, and this value was higher than for STS (71.6 nm) and PE (74.0 nm). However, biofilm formation was faster on STS (6 h) than on PE (12 h), which indicated that surface roughness might not be the only factor that controlled the initiation of biofilm development. Upon detection of the T-RF peaks, richness (S) and diversity indices such as Shannon (H) and Simpson (1/D) demonstrated a rather slow increase until 48 h followed by rapid increase regardless of the pipe materials. Differences of microbial community structures among the biofilm samples were determined based on the cluster analysis using Jaccard coefficients (Sj). Biofilm communities could be divided into two distinct groups according to the exposure time regardless of the pipe materials. First group contained a young (< 48 h) biofilm samples (10 out of 11) but second group contained a mature (<TEX>${\geq}$</TEX> 48 h) samples (11 out of 14). Results suggested that, due to the complexity of biofilm, the targeting of the first group of cluster was crucial for optimizing the management of drinking water distribution systems and controlling microbial growth.

Susceptibility of different phases of biofilm of Klebsiella pneumoniae to three different antibiotics

The existence of majority of bacteria in biofilm mode makes it difficult to eradicate them as antibiotics at much higher concentrations than the MICs are required to destroy these bacteria. This study investigated the effect of different classes of antibiotics on different phases of biofilm formed by Klebsiella pneumoniae. The organism was grown in different phases relevant to biofilm formation: planktonic cells at mid-log phase, planktonic cells at stationary phase, adherent monolayers and mature biofilms and their susceptibility to different classes of antibiotics was assessed. The results showed that planktonic organisms were susceptible to ciprofloxacin, amikacin and piperacillin, and their MBC values were same or eight times higher than their corresponding MICs. MBC of ciprofloxacin and amikacin was found to be four and eight times higher for monolayer than planktonic cells. On the other hand, MBC of piperacillin was >1024 μg ml(-1). K. pneumoniae in a biofilm growth mode was more resistant to antibiotics than all other modes. The effect of amikacin and ciprofloxacin on young and older biofilms, at the highest achievable serum concentrations, was also examined. It was observed that amikacin at a concentration of 40 μg ml(-1) was able to eradicate the young biofilms; however, with increase in the age of the biofilm, it became completely ineffective. Calcofluor staining suggested increased production of exopolysaccharide in older biofilm compared with younger biofim that might be responsible for the increased resistance of older biofilm of K. pneumoniae to antibiotics.

High in vitro antimicrobial activity of β-peptoid–peptide hybrid oligomers against planktonic and biofilm cultures of Staphylococcus epidermidis

An array of β-peptoid–peptide hybrid oligomers displaying different amino acid/peptoid compositions and chain lengths was studied with respect to antimicrobial activity against Staphylococcus epidermidis both in planktonic and biofilm cultures, comparing the effects with those of the common antibiotic vancomycin. Susceptibility and time–kill assays were performed to investigate activity against planktonic cells, whilst confocal laser scanning microscopy was used to investigate the dynamics of the activity against cells within biofilms. All tested peptidomimetics were bactericidal against both exponentially growing and stationary-phase S. epidermidis cells with similar killing kinetics. At the minimum inhibitory concentration (MIC), all peptidomimetics inhibited biofilm formation, whilst peptidomimetics at concentrations above the MIC (80–160μg/mL) eradicated young (6-h-old) biofilms, whilst even higher concentrations were needed to eradicate mature (24-h-old) biofilms completely. Chiral and guanidinylated hybrids exhibited the fastest killing effects against slow-growing cells and had more favourable antibiofilm properties than analogues only containing lysine or lacking chirality in the β-peptoid residues. However, the results of the mature biofilm killing assay indicated more complex structure–activity relationships. Cytotoxicity assays showed a clear correlation between oligomer length and cell toxicity within each subclass of peptides, but all possessed a high differential toxicity favouring killing of bacterial cells. This class of peptidomimetics may constitute promising antimicrobial alternatives for the prevention and treatment of multidrug-resistant S. epidermidis infections.

Investigation of double bond conversion, mechanical properties, and antibacterial activity of dental resins with different alkyl chain length quaternary ammonium methacrylate monomers (QAM)

In order to endow dental resin with antibacterial activity, a series of antibacterial quaternary ammonium methacrylate monomers (QAM) with different substituted alkyl chain length (from 10 to 18) were incorporated into commonly used 2,2-bis[4-(2′-hydroxy-3′-methacryloyloxy-propoxy)-phenyl]propane (Bis-GMA)/triethyleneglycol dimethacrylate (TEGDMA) (50 wt/50 wt) dental resin as immobilized antibacterial agents. Double bond conversion (DC), flexural strength (FS) and modulus (FM), and young and mature biofilms inhibition effectiveness of prepared dental resins were studied and Bis-GMA/TEGDMA without QAM was used as reference. Results showed that there was no significant difference on DC, FS, and FM between copolymer with and without 5 wt% QAM. Substituted alkyl chain length of QAM had no influence on DC, FS, and FM of copolymer, but had influence on antibacterial activity of copolymer. Antibacterial activity of copolymer increased with increasing of substituted alkyl chain length of QAM, and the sequence followed as 5%C10 < 5%C11≈5%C12 < 5%C16≈5%C18. Copolymers containing C18 and C16 had the best inhibition effectiveness on both young biofilm and mature biofilm, copolymers containing C12 and C11 only had inhibition effectiveness on young biofilm and copolymer containing C10 had none inhibition effectiveness on neither young biofilm nor mature biofilm.

Effectiveness of Endodontic Disinfecting Solutions against Young and Old Enterococcus faecalis Biofilms in Dentin Canals

IntroductionEnterococcus faecalis is a species commonly isolated from persistent root canal infections. The purpose of this study was to compare the antibacterial effects of different disinfecting solutions on young and old E. faecalis biofilms in dentin canals using a novel dentin infection model and confocal laser scanning microscopy (CLSM). MethodsThe bacteria were introduced into the dentinal tubules by centrifugation. After 1 day and 3 weeks of incubation, 40 infected dentin specimens were subjected to 1 and 3 minutes of exposure to disinfecting solutions, which included 2% sodium hypochlorite (NaOCl) (EMD Chemicals Inc, Darmstadt, Germany), 6% NaOCl, 2% chlorhexidine (CHX) (Sigma Chemical Co, St Louis, MO), and QMiX (Dentsply Tulsa Dental, Tulsa, OK). The proportions of dead and live bacteria inside the dentinal tubules after exposure to these disinfectants were assessed by CLSM using a LIVE/DEAD bacterial viability stain. ResultsSignificantly fewer bacteria were killed in the 3-week-old dentin biofilm than in the 1-day-old biofilm. Three minutes of exposure resulted in more dead bacteria than 1 minute of exposure for both biofilms in all experimental groups (P < .05). Six percent NaOCl and QMiX were the most effective disinfecting solutions against the young biofilm, whereas against the 3-week-old biofilm, 6% NaOCl was the most effective followed by QMiX. Two percent NaOCl was equally effective as 2% CHX. All the disinfecting agents killed significantly more bacteria than the sterile water used as a negative control (P < .05). ConclusionsWithin dentin canals, bacteria in established biofilms are less easily killed by endodontic medicaments than bacteria in young biofilms.

Pyrosequencing analysis of eukaryotic and bacterial communities in faucet biofilms

In order to understand the microbial communities in drinking water biofilms, both eukaryotic and bacterial communities in three faucet biofilms were characterized by 454 pyrosequencing and quantitative PCR approaches. Microbial assemblages of the biofilms were dominated by bacteria, with Sphingomonadales, Rhizobiales, and Burkholderiales comprising the major bacterial populations. Although about 2years of biofilm development occurred, the microbial community at site WSW still demonstrates the characteristics of a young biofilm community, e.g. low biomass, abundant aggregating bacteria (Blastomonas spp. and Acidovorax spp.) etc. Hartmannella of amoebae was the dominant eukaryotic predator in the biofilms, and correlated closely with biofilm bacterial biomass. Nonetheless, there was no obvious association of pathogens with amoebae in the faucet biofilms. In contrast, residual chlorine seems to be a dominant factor impacting the abundance of Legionella and Mycobacterium, two primary potential opportunistic pathogens detected in all faucet biofilms.

Mature Pseudomonas aeruginosa Biofilms Prevail Compared to Young Biofilms in the Presence of Ceftazidime

Phenotypic tolerances to antibiotics of mature and young Pseudomonas aeruginosa PAO1 biofilms and released planktonic bacteria were compared for four antibiotics. Resistance levels were similar for gentamicin and ciprofloxacin but differed for ceftazidime and meropenem. β-Lactamase mapping showed that, after 5 h of ceftazidime exposure, mature biofilms produced more β-lactamase than young biofilms, facilitating the growth of released planktonic bacteria. This shows the importance of early treatment and choice of antibiotics for P. aeruginosa biofilm infections.

Effects of Xylitol on Xylitol-Sensitive Versus Xylitol-Resistant Streptococcus mutans Strains in a Three-Species in Vitro Biofilm

We studied the effects of xylitol on biofilms containing xylitol-resistant (Xr) and xylitol-sensitive (Xs) Streptococcus mutans, Actinomyces naeslundii and S. sanguinis. The biofilms were grown for 8 and 24 h on hydroxyapatite discs. The viable microorganisms were determined by plate culturing techniques and fluorescence in situ hybridization (FISH) was performed using a S. mutans-specific probe. Extracellular cell-bound polysaccharides (EPS) were determined by spectrofluorometry from single-species S. mutans biofilms. In the presence of 5 % xylitol, the counts of the Xs S. mutans decreased tenfold in the young (8 h) biofilm (p < 0.05) but no effect was seen in the mature (24 h) biofilm. No decrease was observed for the Xr strains, and FISH confirmed these results. No differences were detected in the EPS production of the Xs S. mutans grown with or without xylitol, nor between Xr and Xs S. mutans strains. Thus, it seems that xylitol did not affect the EPS synthesis of the S. mutans strains. Since the Xr S. mutans strains, not inhibited by xylitol, showed no xylitol-induced decrease in the biofilms, we conclude that growth inhibition could be responsible for the decrease of the counts of the Xs S. mutans strains in the clinically relevant young biofilms.

Aquatic protists modulate the microbial activity associated with mineral surfaces and leaf litter

Aquatic heterotrophic protists structure biofilm morphology and stimulate organic matter processing, but knowledge about their effects on the activity of surface-associated commu- nities is still missing. Microcosm experiments revealed that the community respiration of young biofilms (7 d old) at mineral surfaces was not affected by co-cultivation with the raptorial feeder Chilodonella uncinata or the suspension feeder Tetrahymena pyriformis. However, grazing by both ciliates reduced the bacterial abundance and probably enhanced nutrient availability by recycling. Our data indicated an increased individual bacterial activity under grazing pressure, resulting in no net effect on the community respiration. In a second experiment, the respiration of leaf-associated microbial communities composed of the fungus Heliscus lugdunensis and a multi- species bacterial assemblage was significantly enhanced in the presence of T. pyriformis after 7 d of incubation. The stimulation was observed under both normoxic (turbulent) and hypoxic (turbu- lent and stagnant) conditions. After longer incubation, presumably matching an advanced phase of leaf degradation, T. pyriformis did not affect community respiration exposed to hypoxic stag- nant conditions. In contrast to former studies, no impact of protists on leaf mass loss was observed. By stimulating leaf-associated community respiration, protists seem to affect processes involved in the initial phase of leaf processing.

Incorporation of an antibacterial and radiopaque monomer in to dental resin system

ObjectivesThe purpose of this study was to prepare antibacterial and radiopaque dental resin through adding one polymerizable quaternary ammonium compound with iodine as counter anion into Bis-GMA/TEGDMA (50/50, wt/wt) dental resin system, and evaluate the degree of monomer conversion, mechanical properties, radiopacity, and antibacterial effectiveness of the polymer. Methods2-Dimethyl-2-dodecyl-1-methacryloxyethyl ammonium iodine (DDMAI) (3wt.% and 5wt.%) was added into a Bis-GMA/TEGDMA (50/50, wt/wt) resin system with CQ (0.7wt.%) and DMAEMA (0.7wt.%) as photoinitiation system. Degree of monomer conversion (DC) was determined by FT-IR analysis. The flexural strength (FS) and flexural modulus (FM) of the polymer were measured using a three-point bending set up. Radiographs were taken to determine the radiopacity of the polymer, and aluminum step-wedge (0.5–4mm) was used as calibration standard. A single-species biofilm model with Streptococcus mutans as the tests organism was used to evaluate the antibacterial property of the polymer. Bis-GMA/TEGDMA without DDMAI was used as control material in all of the tests. ResultsANOVA analysis revealed that there was no significant difference in DC between polymer with and without DDMAI (p>0.05). Polymer with 3wt.% DDMAI had higher FS than the control material (p<0.05), while polymer with 5wt.% DDMAI had comparable FS with the control material (p>0.05). Though average FM of control material was lower than that of 3wt.% DDMAI containing polymer and higher than 5wt.% DDMAI containing polymer, but the differences were statistically insignificant. By increasing the quantity of DDMAI, the radiopacity of the polymer increased. Of the three formulations, the polymer with 5wt.% DDMAI inhibited biofilm the formation of the clinically relevant young biofilm. SignificanceIncorporation of DDMAI into resin system could endow it with radiopacity and antibacterial effectiveness, and these two properties seem to be improved with increasing the quantities of DDMAI.

Effect of Levofloxacin and Vitamin C on Bacterial Adherence and Preformed Biofilm on Urethral Catheter Surfaces

Catheter associated urinary tract infection (CAUTI) is one of the most common types of hospital acquired infection. Several studies have confirmed its significant contribution in increasing the morbidity, mortality, hospital stay and costs. The normal function of the urinary tract is usually altered by the presence of a catheter and this makes it easier for bacteria to become established in the bladder and cause serious infection. A wide range of persistent catheter related infections may be related to the ability of bacteria to form biofilms. In this regards, the treatment of device related infections with conventional antimicrobial agents frequently fails because microorganisms growing in biofilms are more tolerant or phenotypically resistant to antimicrobial agents than planktonic (free) cells. A mature biofilm can even tolerate antibiotics at concentrations of 10-1000 times more than required to kill planktonic bacteria. In this regard, fluoroquinolones (The most common clinically used members of the quinolones antibiotics) have been reported as an effective treatment in case of both young and mature biofilms because of their good penetrative qualities. Norrby et al. have reported that among the recently developed fluoroquinolones, levofloxacin is widely used in clinical practice and it is less likely to select resistant strains compared with other group members. Therefore, levofloxacin represent a promising candidate to treat tedious infections such as those of biofilm forming bacteria.

Cohesiveness and hydrodynamic properties of young drinking water biofilms

Drinking water biofilms are complex microbial systems mainly composed of clusters of different size and age. Atomic force microscopy (AFM) measurements were performed on 4, 8 and 12 weeks old biofilms in order to quantify the mechanical detachment shear stress of the clusters, to estimate the biofilm entanglement rate ξ. This AFM approach showed that the removal of the clusters occurred generally for mechanical shear stress of about 100 kPa only for clusters volumes greater than 200 μm 3. This value appears 1000 times higher than hydrodynamic shear stress technically available meaning that the cleaning of pipe surfaces by water flushing remains always incomplete. To predict hydrodynamic detachment of biofilm clusters, a theoretical model has been developed regarding the averaging of elastic and viscous stresses in the cluster and by including the entanglement rate ξ. The results highlighted a slight increase of the detachment shear stress with age and also the dependence between the posting of clusters and their volume. Indeed, the experimental values of ξ allow predicting biofilm hydrodynamic detachment with same order of magnitude than was what reported in the literature. The apparent discrepancy between the mechanical and the hydrodynamic detachment is mainly due to the fact that AFM mechanical experiments are related to the clusters local properties whereas hydrodynamic measurements reflected the global properties of the whole biofilm.