Controlling bacterial fouling with polyurethane/N-halamine semi-interpenetrating polymer networks.

N -halamine-based interpenetrating polymer networks were developed as a simple and effective strategy in the preparation of antimicrobial polymers. An N-halamine monomer, N-chloro-2, 2, 6, 6-tetramethyl-4-piperidyl methacrylate, was incorporated into polyurethane in the presence of a cross-linker and an initiator. Post-polymerization of the monomers led to the formation of polyurethane/N-halamine semi-interpenetrating polymer networks. The presence of N-halamines in the semi-interpenetrating polymer networks was confirmed by attenuated total reflectance infrared, water contact angle, and energy-dispersive X-ray spectroscopy analysis. The N-halamine contents in the semi-interpenetrating polymer networks could be readily controlled by changing reaction conditions. The distribution of active chlorines within the semi-interpenetrating polymer networks was characterized with energy-dispersive X-ray spectroscopy. Contact mode antimicrobial tests, zone of inhibition studies, and scanning electron microscopy observations showed that the semi-interpenetrating polymer networks had potent antimicrobial and antifouling effects against both Gram-positive and Gram-negative bacteria. Release tests demonstrated the outstanding stability of the N-halamine structures in the new semi-interpenetrating polymer networks.

Fluorinated and Un-fluorinated N-halamines as Antimicrobial and Biofilm-controlling Additives for Polymers.

The objective of this study was to evaluate the effects of fluorination on the antimicrobial and biofilm-controlling activities of N-halamine-based additives for polymers. A fluorinated N-halamine, 1-chloro-3-1H,1H,2H,2H-perflurooctyl-5,5-dimetylhydantoin (Cl-FODMH), and its un-fluorinated counterpart, 1-chloro-3-octyl-5,5-dimethylhydantoin (Cl-ODMH), were synthesized and characterized with FT-IR, 1H-NMR, and DSC studies. Polyurethane (PU) films containing Cl-ODMH and Cl-FODMH as antimicrobial additives were fabricated through solvent casting. With the same additive contents (1wt%-5 wt%), PU films with Cl-FODMH showed higher contact angle values. AFM, SEM and DSC results revealed that while Cl-ODMH distributed evenly within PU, Cl-FODMH aggregated and formed macro-domains in PU. Antimicrobial studies showed that PU films with Cl-ODMH had higher antimicrobial and biofilm-controlling potency against Gram-positive and Gram-negative bacteria than PU samples with Cl-FODMH. These results demonstrated the importance of distribution of additives in polymers on antimicrobial performances, shedding lights on future antimicrobial material design strategies.

Acyclic N-halamine-immobilized polyurethane: Preparation and antimicrobial and biofilm-controlling functions.

Hydroxyl groups were introduced onto polyurethane surfaces through 1,6-hexamethylene diisocyanate activation, followed by diethanolamine hydroxylation. Polymethacrylamide was covalently attached to the hydroxylated polyurethane through surface grafting polymerization of methacrylamide using cerium (IV) ammonium nitrate as an initiator. After bleach treatment, the amide groups of the covalently bound polymethacrylamide chains were transformed into N-halamines. The new N-halamine-immobilized polyurethane provided a total sacrifice of 107-108 colony forming units per milliliter of Staphylococcus aureus (Gram-positive bacteria), Escherichia coli (Gram-negative bacteria), and Candida albicans (fungi) within 10 min and successfully prevented bacterial and fungal biofilm formation. The antimicrobial and biofilm-controlling effects were both durable and rechargeable, pointing to great potentials of the new acyclic N-halamine-immobilized polyurethane for a broad range of related applications.

Evaluation of 3 dental unit waterline contamination testing methods.

Previous studies have found inconsistent results from testing methods used to measure heterotrophic plate count (HPC) bacteria in dental unit waterline (DUWL) samples. This study used 63 samples to compare the results obtained from an in-office chairside method and 2 currently used commercial laboratory HPC methods (Standard Methods 9215C and 9215E). The results suggest that the Standard Method 9215E is not suitable for application to DUWL quality monitoring, due to the detection of limited numbers of heterotrophic organisms at the required 35°C incubation temperature. The results also confirm that while the in-office chairside method is useful for DUWL quality monitoring, the Standard Method 9215C provided the most accurate results.

A survey of infection control teaching in U.S. dental schools.

This study was conducted to determine the content of infection control (IC) curricula, the extent of IC monitoring and compliance, and the number of bloodborne pathogen (BBP) exposures/year in U.S. dental schools. A questionnaire was emailed to persons responsible for predoctoral IC programs. The response rate was 60 percent. Most schools did not have an independent course and used classroom lectures and clinic demonstrations to teach IC. Schools with an IC committee were more likely to use online learning (p<0.05), utilize multiple teaching methods (p<0.05), issue written warnings for IC violations (p<0.0001), and use multiple disciplinary actions (p<0.005) than schools without an IC committee. Schools with an IC coordinator were less likely to issue grade reductions for IC violations than schools with no IC coordinator (p<0.05). Thirty-eight percent reported ≥ 16 BBP exposures/year, and 18 percent reported <5. There was significant correlation between BBP exposure incidents and large class size (p<0.005). Respondents were satisfied with their IC curriculum and perceived that dental students had a high level of IC compliance and satisfaction, along with staff IC promotion and compliance. The findings suggest that schools without an IC committee should consider its benefits. Further investigation of schools with high numbers of BBP exposures is recommended.

A comparison of 2 laboratory methods to test dental unit waterline water quality.

The performance of 2 American Public Health Association standard laboratory methods, the R2A spread plate and the SimPlate(TM) for heterotrophic plate count, for quantifying heterotrophic microorganisms in dental waterline samples was evaluated. Microbial counts were underestimated on SimPlate(TM) compared with R2A, and the results indicated a poor correlation between the 2 methods.

An N-halamine-based rechargeable antimicrobial and biofilm controlling polyurethane.

An N-halamine precursor, 5,5-dimethylhydantoin (DMH), was covalently linked to the surface of polyurethane (PU) with 1,6-hexamethylene diisocyanate (HDI) as the coupling agent. The reaction pathways were investigated using propyl isocyanate (PI) as a model compound. The results suggested that the imide and amide groups of DMH have very similar reactivities toward the isocyanate groups on PU surfaces activated with HDI. After bleach treatment the covalently bound DMH moieties were transformed into N-halamines. The new N-halamine-based PU provided potent antimicrobial effects against Staphylococcus aureus (Gram-positive bacterium), Escherichia coli (Gram-negative bacterium), methicillin-resistant Staphylococcus aureus (MRSA, drug-resistant Gram-positive bacterium), vancomycin-resistant Enterococcus faecium (VRE, drug-resistant Gram-positive bacterium), and Candida albicans (fungus), and successfully prevented bacterial and fungal biofilm formation. The antimicrobial and biofilm controlling effects were stable for longer than 6 months under normal storage in open air. Furthermore, if the functions were lost due to prolonged use they could be recharged by another chlorination treatment. The recharging could be repeated as needed to achieve long-term protection against microbial contamination and biofilm formation.

Rechargeable biofilm-controlling tubing materials for use in dental unit water lines.

A simple and practical surface grafting approach was developed to introduce rechargeable N-halamine-based antimicrobial functionality onto the inner surfaces of continuous small-bore polyurethane (PU) dental unit waterline (DUWL) tubing. In this approach, tetrahydrofuran (THF) solution of a free-radical initiator, dicumyl peroxide (DCP), flowed through the PU tubing (inner diameter of 1/16 in., or 1.6 mm) to diffuse DCP into the tubing's inner walls, which was used as initiator in the subsequent grafting polymerization of methacrylamide (MAA) onto the tubing. Upon chlorine bleach treatment, the amide groups of the grafted MAA side chains were transformed into acyclic N-halamines. The reactions were confirmed with attenuated total reflectance infrared (ATR) spectra and iodometric titration. The mechanical properties of the tubing were not significantly affected by the grafting reactions. The biofilm-controlling function of the new N-halamine-based PU tubing was evaluated with Pseudomonas aeruginosa (P. aeruginosa), one of the most isolated water bacteria from DUWLs, in a continuous bacterial flow model. Bacteria culturing and SEM studies showed that the inner surfaces of the new N-halamine-based PU tubing completely prevented bacterial biofilm formation for at least three to four weeks. After that, bacteria began to colonize the tubing surface. However, the lost function was fully regenerated by exposing the tubing inner surfaces to diluted chlorine bleach. The recharging process could be repeated periodically to further extend the biofilm-controlling duration for long-term applications.

The biofilm-controlling functions of rechargeable antimicrobial N-halamine dental unit waterline tubing.

OBJECTIVE: A study was conducted to test the biofilm-controlling functions of N-halamine tubing over an eight-month period. METHODS: A laboratory system, simulating a teaching dental clinic, was used to test rechargeable N-halamine tubing (T) compared to an untreated control (C) using the unit manufacturer's tubing. For the long-term study, a recharged tubing (RC) treated with bleach was used to compare with the test (T) and the control (C) tubing. Source tap water was cycled through the lines at 1.4 mL/minute, five minutes on and 25 minutes off, eight hours/day, five days/week. Every three weeks, samples of effluent, recovered adherent bacteria from inside tubing surfaces, and SEM images were examined for bacterial and biofilm growth. After sampling, a recharging solution of chlorine bleach (1 : 10 dilution) was run through T and RC lines, left overnight, and rinsed out the next morning. One-way ANOVAs and Spearman correlations were performed to detect significant differences for T, RC, and C, and determine significance with time period and source water, respectively. RESULTS: Mean log CFU/mL for C effluent > T (p = 0.028), and C tubing > T (p = 0.035). Spearman correlations were significant between effluent and source water level for T (rho = 0.817), and T tubing (0.750); between RC tubing and source water level (rho = 0.836), and time (rho = 0.745); and between C and time (rho = 0.873). SEM imaging confirmed the presence of biofilm inside RC and C, but not inside T. CONCLUSION: N-halamine tubing completely inhibited biofilm formation without negatively affecting the physical properties of the effluent water. Further research on N-halamine tubing using a pure water source is recommended, as T effluent bacterial levels reflected the source tap water quality and proliferation of planktonic bacteria with no biofilm activity.

Growth and identification of bacteria in N-halamine dental unit waterline tubing using an ultrapure water source.

This study examined bacterial growth and type on biofilm-controlling dental unit waterline (DUWL) tubing (T) and control manufacturer's tubing (C) in a laboratory DUWL model using ultrapure source water that was cycled through the lines. Sections of tubing lines were detached and examined for biofilm growth using SEM imaging at six sampling periods. Bacteria from inside surfaces of T and C, source unit, and reservoir were cultured and enumerated. At six months, organisms were molecularly identified from the alignment matches obtained from the top three BLAST searches for the 16S region. There was a 1-3 log increase in organism growth in a clean, nonsterile reservoir within an hour. Biofilm was established on the inside surfaces of C within three weeks, but not on T. Proteobacteria, and Sphingomonas spp. were identified in the source reservoir and C line, and a variation of the genera was found in T line.

Amine, Melamine, and Amide N-Halamines as Antimicrobial Additives for Polymers.

N-chloro-2,2,6,6-tetramethyl-4-piperidinol laurate (Cl-TMPL) was prepared by reacting 2,2,6,6-tetramethyl-4-piperidinol hydrochloride (TMP·HCl) with lauroyl chloride, followed by chlorination with sodium dichloroisocyanurate. The chemical structure of Cl-TMPL was characterized with FT-IR, NMR, DSC, and TGA analyses. The antimicrobial performance of Cl-TMPL against Gram-positive and Gram-negative bacteria was compared with 1-chloro-3-dodecyl-5,5-dimethylhydantoin (Cl-DDMH), a amide N-halamine, and chloro-2,4-diamino-6-dodecyl-1,3,5-triazine (Cl-DADT), a melamine (imino) N-halamine. The three classes of N-halamines were used as additives for polyurethane (PU). Visible light transparency data indicated that up to 6% of Cl-DDMH or Cl-DADT could be compatibly mixed with PU, but Cl-TMPL had low compatibility with PU at higher than 2% of Cl-TMPL. With the same additive content, Cl-DDMH and Cl-DADT provided more powerful antimicrobial and biofilm-controlling effects than Cl-TMPL. In stability studies, however, PU samples with Cl-TMPL released the lowest amount of active chlorine into the immersing solution, suggesting the highest stability of the antimicrobial and biofilm-controlling efficacy.

Dental unit waterline contamination--a review.

Manufacturers of dental units have responded positively to the challenge from the American Dental Association (ADA) and the subsequent guidelines issued by the Centers for Disease Control and Prevention (CDC) to deliver patient treatment water that is at least as pure as drinking water. Dental units are now routinely manufactured with anti-retraction devices that are designed to control oral fluids from being aspirated into the lines during treatment and many units have water systems that isolate source water from municipal water supply. The dental industry has also produced an array of devices and cleaning/disinfectant products to further facilitate the use of clean patient treatment water. Products that claim disinfectant efficacy must be registered with the Environmental Protection Agency (EPA). If they are not EPA-registered, they can be labeled as waterline cleaners only. Waterline treatment devices that are sold separately and require connection to dental units must be registered with the Food and Drug Administration (FDA) as medical devices. Patient treatment water quality can be monitored by using in-office chairside kits or through commercial laboratory services.

The effect of frequent clinical use of dental unit waterlines on contamination.

Three dental units with self-contained water systems in an outpatient teaching dental clinic were treated with a proprietary chlorine dioxide waterline cleaner. Three similar units were used as controls. After four weeks, test and control units were crossed over. Water samples were taken from each line on each unit and from the sink faucets at six time periods; and the frequency of use of each line was recorded. Statistical analysis showed that increased frequency of use of waterlines did not affect lines that were chemically treated, but was associated with less contamination of untreated lines.

Tuberculosis: infection control/exposure control issues for oral healthcare workers.

AIM: The aim is to present the essential elements of an infection control/exposure control plan for the oral healthcare setting with emphasis on tuberculosis (TB). METHODS AND MATERIALS: A comprehensive review of the literature was conducted with special emphasis on TB infection-control issues in the oral healthcare setting. RESULTS: Currently available knowledge related to TB infection-control issues is supported by data derived from well-conducted trials or extensive controlled observations. In the absence of supportive data the information is supported with the best-informed, most authoritative opinion available. CONCLUSION: Essential elements of an effective TB infection-control plan include a three-level hierarchy of administrative, environmental, and respiratory-protection controls. CLINICAL SIGNIFICANCE: Standard precautions provide the fabric for strategies to prevent or reduce the risk of exposure to bloodborne pathogens and other potentially infectious material. However, standard precautions are inadequate to prevent the spread of organisms through droplet nuclei 1-5 micron in diameter and additional measures are necessary to prevent the spread of Mycobacterium tuberculosis. Oral healthcare settings have been identified as outpatient settings in which patients with suspected or confirmed infectious TB disease are expected to be encountered. Therefore, oral healthcare settings must have a written TB infection-control program.

Measuring the validity of two in-office water test kits.

BACKGROUND: The authors conducted a study to determine the validity of two commercially available in-office water test kits compared with a spread plate technique using the gold standard dehydrated culture medium R2A agar for monitoring the quality of dental treatment water. METHODS: Over a 12-week period, one author monitored nine dental units in a dental school that each were equipped with an independent water reservoir. The author collected 351 split samples, cultured them using three test methods, counted bacterial colonies manually and assessed validity using two cutoff values: < or = 200 colony-forming units per milliliter (CFU/mL) (an American Dental Association goal) and < or = 500 CFU/mL (a Centers for Disease Control and Prevention [CDC] recommendation and a U.S. Environmental Protection Agency [EPA] mandate). RESULTS: Of the 351 split samples processed, the in-office test kits' accuracy ranged from 25 to 69 percent, according to the ADA and CDC/EPA recommendations, compared with the R2A agar. CONCLUSIONS: Overall, the in-office test kits underestimated bacteria levels, producing inaccurate measurements of bacterial levels compared with the R2A agar. CLINICAL IMPLICATIONS: The data suggest that use of the two in-office test kits could result in a lack of compliance, owing to underestimating bacterial contamination with recognized recommendations for dental unit waterline quality.

Reduction of bacterial levels in dental unit waterlines.

OBJECTIVES: To test the efficacy of an intermittent use, dental unit waterline cleaner, containing 0.12% chlorhexidine, in a proprietary formulation, to reduce bacterial levels in three functioning dental units with independent water reservoir systems. METHOD AND MATERIALS: Baseline water samples were first taken from six units. Two ounces of the undiluted test product was run through lines, left overnight, and flushed out the next morning. This was repeated for 6 nights initially, and once a week thereafter for 12 weeks. Three control dental units did not have chemicals added. Weekly samples were collected in bottles containing sodium thiosulphate on the afternoon before overnight treatment, plated on R2A agar, and incubated at room temperature for 7 days. RESULTS: Mean colony-forming units per millimeter (CFU/mL) in treatment units declined from 23,389 (+/- 20,085) at baseline, to 6 (+/- 10) in week 4, to 5 (+/- 2) in week 12. Statistical analysis showed a significant difference between treatment and control units. CONCLUSION: Intermittent treatment of dental unit waterlines with 0.12% chlorhexidine gluconate (CHX), in a proprietary formulation, resulted in significantly reduced bacterial counts to levels that were consistently below the American Dental Association's goal of 200 CFU/mL for 8 weeks.

Isolation of an unusual fungus in treated dental unit waterlines.

BACKGROUND: Numerous organisms have been identified in dental unit waterlines, or DUWLs. Decontamination of DUWLs focuses on maintaining heterotrophic, mesophilic bacteria below 200 colony-forming units per milliliter as recommended by the ADA. METHODS: The authors conducted a study to test the efficacy of a continuous-use, stabilized chlorine dioxide proprietary compound to decrease the number of bacteria in DUWLs. The authors used three dental units with self-contained water systems to test the product and three similar units as controls. They aseptically collected water samples weekly according to recommended methods, plated the samples on R2A agar and incubated them for seven days. RESULTS: The authors isolated heterotrophic, mesophilic bacteria from treatment and control units for eight weeks. In the ninth week, the predominant isolates from one of the treatment units changed in appearance to small, dark, shiny colonies that the authors tentatively identified as fungal. The authors then isolated similar colonies from the source tap water and ultrasonic and handpiece lines. They added three additional dental units from the same clinic in the sixth week of the study and isolated similar fungal colonies from them after five weeks of treatment. The authors performed DNA sequencing with an automated sequencer and identified the organism Exophiala mesophila. CONCLUSIONS: The authors did not observe fungal isolates in the control units, which suggests that continuous waterline treatment may cause proliferation of a fungus present in small amounts in source water. CLINICAL IMPLICATIONS. The findings of this study indicate the need to monitor water quality regularly when treating waterlines with continuous-use chemical cleaners.

The efficacy of a continuous-use stabilized chlorine dioxide dental unit waterline cleaner and the evaluation of two water sampling methods.

Many commercial dental unit waterline cleaners are available. Results regarding the efficacy of these products vary and sampling methods and laboratory procedures can affect results. This study was conducted to test the efficacy of a continuous-use stabilized chlorine dioxide product and determine if two different sampling methods produced the same results. There was a statistically significant difference between the treated units and the control units (p < 0.05) but the two sampling methods revealed no statistically significant difference (p > 0.5). Treated units showed a decline in the mean number of colony forming units per milliliter (CFU/mL) over the study period but the level was not consistently low enough to meet the ADA-recommended levels of 200 CFU/mL. The findings of this study indicate that it is not necessary to replace a continuous use product with fresh, untreated water when testing water quality.