Dental unit waterlines: biofilms, disinfection and recurrence

Antimicrobial effects of automobile screenwashes against Legionella pneumophila

AIMS

Legionella pneumophila (Lp), a human pathogen, has been detected in windscreen wiper fluid reservoirs (WWFRs) where commercial screenwashes (CSWs) are commonly added. Limited information is available on CSWs against planktonic Lp; however, responses of sessile Lp and planktonic Lp pre-acclimated in nutrient-limited water to CSWs remain unknown. This study thus investigates the antibacterial effects of CSWs on sessile and starved planktonic Lp, in comparison with unstarved Lp.

METHODS AND RESULTS

Lp biofilms were produced on glass and WWFR materials of high-density polyethylene (HDPE) and polypropylene (PP). Planktonic Lp with and without acclimation in tap water were prepared. Log reductions in cell counts averaged 0.4-5.0 for ten brands of CSWs against sessile Lp and 1.0-3.9 and 0.9-4.9, respectively, against starved and unstarved planktonic Lp for five CSWs. Both biofilm formation and acclimation in tap water enhanced Lp resistance to CSWs. Significantly different log-reduction values among CSW brands were observed for sessile Lp on HDPE and planktonic Lp regardless of acclimation (p<0.05).

CONCLUSIONS

Biofilm formation, starvation acclimation, and CSW brand are crucial factors influencing Lp response to CSWs.

SIGNIFICANCE AND IMPACT OF STUDY

This study advances the knowledge of Lp reaction in anthropogenic water systems with CSWs.

World Small Animal Veterinary Association Global Dental Guidelines

Dental, oral, and maxillofacial diseases are some of the most common problems in small animal veterinary practice. These conditions create significant pain as well as localized and potentially systemic infection. As such, the World Small Animal Veterinary Association (WSAVA) believes that un- and under treated oral and dental diseases pose a significant animal welfare concern. Dentistry is an area of veterinary medicine which is still widely ignored and is subject to many myths and misconceptions. Effective teaching of veterinary dentistry in the veterinary school is the key to progression in this field of veterinary medicine, and to the improvement of welfare for all our patients globally. These guidelines were developed to provide veterinarians with the information required to understand best practices for dental therapy and create realistic minimum standards of care. Using the three-tiered continuing education system of WSAVA, the guidelines make global equipment and therapeutic recommendations and highlight the anaesthetic and welfare requirements for small animal patients. This document contains information on common oral and dental pathologies, diagnostic procedures (an easily implementable and repeatable scoring system for dental health, dental radiography and radiology) and treatments (periodontal therapy, extractions). Further, there are sections on anaesthesia and pain management for dental procedures, home dental care, nutritional information, and recommendations on the role of the universities in improving veterinary dentistry. A discussion of the deleterious effects of anaesthesia free dentistry (AFD) is included, as this procedure is ineffective at best and damaging at worst. Throughout the document the negative effects of undiagnosed and/or treated dental disease on the health and well-being of our patients, and how this equates to an animal welfare issue, is discussed.

Three key factors influencing the bacterial contamination of dental unit waterlines: a 6-year survey from 2012 to 2017

BACKGROUND

The contaminated output water from dental unit waterlines (DUWLs) is a potential risk to both patients and dental personnel who are frequently exposed to this water or aerosols.

AIM

The purpose was to evaluate the contamination level and prevalence of bacteria in the output water of DUWLs, and to identify key factors to provide technical support for formulating relevant policies.

METHODS

We developed a special sampling connector designed for collecting dental handpiece output water and a measurement device to assess retraction of a dental chair unit (DCU). Output water from dental handpieces and air/water syringes were collected as representative of DUWLs. Water samples were tested with reference to China's national standard.

FINDINGS

From 2012 to 2017, 318 DCUs were randomly selected from 64 hospitals in Tianjin, China. Of these DCUs, 78.93% had no disinfection to prevent DUWL contamination. Three-hundred and forty-three (56.14%) samples complied with the guidelines on DUWL output water. The highest concentration of bacteria was 1.8 × 10⁶  colony-forming units (CFUs)/mL. The three key factors of influence were as follows: daily or weekly disinfection of DUWLs; water supply source being hospital self-made purified water or purchased purified bottled water; and DCU with a valid anti-retraction valve. Potential infectious agents, including Bacillus cereus, Burkholderia cepacia and Pseudomonas aeruginosa, were isolated.

CONCLUSION

There was a high rate of contamination in DUWLs. This highlights the need to develop national standards. There is a need to disinfect the DUWLs periodically and use a cleaner source of water; more attention should be paid to the efficacy of DCU anti-retraction valves.

Substantivity of hypochlorous acid-based disinfectant against biofilm formation in the dental unit waterlines

Objective:

The purpose of the study was to examine the substantivity of a new disinfectant against biofilm formation in the dental unit waterlines.

Materials and Methods:

Twenty dental units were selected for the study and divided into two groups: Group A (dental unit waterlines treated with the disinfectant) and Group B (untreated dental unit waterlines). Biofilm formation was monitored in both groups by removing the one dental unit waterline from each group for the period of 10 days. One inch of the dental unit waterline tube was cut at random site, and the inner lumen of the cut sections was analyzed using the scanning electron microscope (SEM) (TESCAN VEGA3 SBU).

Results:

On examination, SEM images showed that there was no slime layer or bacterial cells seen in cut section for the period of 7 days in the treated dental waterlines, which means that there is no evident of biofilm formation. In the untreated dental unit waterline cut section, slime layer was observed from day 1.

Conclusion:

Disinfectant solution was proved to be effective for 7 days against biofilm formation. This technique could be used as a valid method for disinfection of dental unit waterlines.

Evaluation of bacterial contamination of dental unit waterlines and use of a newly designed measurement device to assess retraction of a dental chair unit

INTRODUCTION

Dental unit waterline (DUWL) output water is delivered through instruments of a dental chair unit (DCU) to irrigate and cool teeth. However, these waterlines can be heavily contaminated with bacteria.

AIM

The purpose of the present study was to assess retraction and investigate the contamination level and prevalence of bacteria in DUWL output water.

METHODS

Fifty-eight DCUs were randomly selected from 30 hospitals in 10 districts of Tianjin, one of the four special municipalities of China. A unique sampling connector was used in place of the dental handpiece to collect water samples. Evaluation of retraction was accomplished using a retraction measurement device designed in accordance with the International Standard ISO 7494-2:2015(E).

RESULTS

A total of 263 water samples were collected, and the highest concentration of bacteria [1.8 × 10(6) colony-forming units (CFU)/mL] was found in the handpiece group. Thirty (51.72%) water samples in the handpiece group and 21 (36.21%) in the air/water syringe groups were cultured, yielding colony counts of > 500 CFU/mL. Potential infectious agents, such as Bacillus cereus, Kocuria kristinae and Pseudomonas fluorescens, were isolated from the water samples. Thirty (51.72%) DCUs failed the retraction evaluation. There was a significant, positive correlation (P < 0.05) between the concentration of bacteria in the water sample and the retracted volume.

CONCLUSION

It is of paramount importance to increase compliance with the standards for controlling DUWL contamination. Routine microbial monitoring and evaluation of retraction are necessary to provide high-quality water for use in dental treatment.

Investigation of the bacterial load and antibiotic susceptibility of dental units

The aim of this study was to evaluate the bacterial contamination level and to determine the antibiotic susceptibility of the isolated bacteria from dental unit waterlines (DUWLs) in Istanbul. Bacterial quality of DUWLs is very important, as patients and dental staff are regularly exposed to water and aerosols generated by the unit. If opportunistic pathogens such as Staphylococcus aureus, Pseudomonas aeruginosa, and Legionella pneumophila are present in DUWLs, patient and dental staff can be infected. One hundred water samples were collected from high-speed drills and input waters from 50 dental units. Aerobic heterotrophic bacteria counts and the presence of Legionella, Pseudomonas, oral streptococci, and Staphylococcus were investigated in dental unit waters and aerosol samples. In addition, the antibiotic susceptibility of the isolated and identified bacteria from DUWLs was examined. This research found that 37 out of 50 dental unit water samples exceeded the American Dental Association's limit of 200 colony-forming units (CFU)/mL(-1). Legionella, oral streptococci, and S. aureus were not detected in any water or aerosol samples, but P. aeruginosa was isolated in three DUWLs. Also, Pseudomonas and Staphylococcus were found in water and aerosol samples. Cefoperazone, ofloxacin, gentamicin, ciprofloxacin, and piperacillin were the most effective antibiotics against the isolated bacteria from DUWLs.

Bacterial contamination of dental unit waterlines

Safety of patients and dental personnel requires the appropriate microbiological water quality in dental units. During treatment, patients and dental workers are exposed both to direct contact with bacteria-contaminated water in the form of splatter and with contaminated water aerosol emitted during work by unit handpieces, including rotating and ultrasonic instruments. The aim of the study was to determine the qualitative and quantitative contamination of water in dental unit reservoirs with aerobic and facultative anaerobic bacteria. The study material included water sampled from 107 dental unit reservoirs located in dental surgeries of public health centres. Conventional microbiological methods were used to identify microorganisms. The study shows that the contamination of water in dental unit reservoirs with aerobic and facultative anaerobic bacteria is commonplace. The mean concentration of mesophile bacteria in dental unit reservoir water exceeded 1.1 × 10(5) cfu/ml. The prevailing species were Gram-negative bacteria of the families Burkholderiaceae, Pseudomonadaceae, Ralstoniaceae and Sphingomonadaceae. The most numerous bacteria were Ralstonia pickettii, constituting 49.33 % of all the identified aerobic and facultative anaerobic bacteria. Among Gram-positive rods, the most numerous were bacteria of the genus Brevibacterium (5.83 %), while the highest percentage shares (13.25 %) of all Gram-positive microorganisms were found for Actinomyces spp. The study confirms the necessity of regular monitoring of microbial contamination of dental unit waterlines (DUWL) and use of various water treatment procedures available to disinfect DWUL.

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.

Inhibitory effect of biocides on the viable masses and matrices of Staphylococcus aureus and Pseudomonas aeruginosa biofilms

Bacteria and matrix are essential for the development of biofilms, and assays should therefore target both components. The current European guidelines for biocidal efficacy testing are not adequate for sessile microorganisms; hence, alternative discriminatory test protocols should be used. The activities of a broad range of biocides on Staphylococcus aureus and Pseudomonas aeruginosa biofilms were evaluated using such in vitro assays. Nearly all selected biocides showed a significant decrease in S. aureus biofilm viability, with sodium hypochlorite and peracetic acid as the most active biocides. Only hydrogen peroxide and sodium hypochlorite showed some inhibitory effect on the matrix. Treatment of P. aeruginosa biofilms was roughly comparable to that of S. aureus biofilms. Peracetic acid was the most active on viable mass within 1 min of contact. Isopropanol ensured a greater than 99.999% reduction of P. aeruginosa viability after at least 30 min of contact. Comparable to results with S. aureus, sodium hypochlorite and hydrogen peroxide markedly reduced the P. aeruginosa matrix. This study clearly demonstrated that despite their aspecific mechanisms of action, most biocides were active only against biofilm bacteria, leaving the matrix undisturbed. Only hydrogen peroxide and sodium hypochlorite were active on both the biofilm matrix and the viable mass, making them the better antibiofilm agents. In addition, this study emphasizes the need for updated and standardized guidelines for biofilm susceptibility testing of biocides.

Assessment of inhibitory effects of fluoride-coated tubes on biofilm formation by using the in vitro dental unit waterline biofilm model

This study aimed to establish an in vitro model to simulate biofilms formed in dental unit waterlines (DUWLs) and to investigate the ability of polyvinylidene fluoride (PVDF)-coated tubes to inhibit biofilm formation using this model. The water and biofilm samples were obtained from DUWLs which had been clinically used for 2.5 years, and the predominant bacteria were identified. A conventional polyurethane tube was incubated for 24 to 96 h in the mixed flora of isolated bacteria, and the optimal incubation conditions to simulate a clinically formed biofilm were determined by observation with a scanning electron microscope. Biofilm formation on a PVDF-coated tube was observed using this in vitro model, and the adherence of different bacterial species to conventional and PVDF-coated tubes was assessed. Sphingomonas paucimobilis, Acinetobacter haemolytics, and Methylobacterium mesophilicum were predominantly isolated from contaminated DUWLs. Incubation of the polyurethane tube with the mixed flora containing these three species for 96 h resulted in the formation of a mature biofilm similar to the one clinically observed. The PVDF-coated tube was significantly less adhesive to all three bacterial species than the polyurethane tube (P < 0.05 by the Mann-Whitney U test), and the attachment of small amounts of rods was observed even after incubation with the mixed flora for 96 h. In conclusion, an in vitro biofilm model was obtained by using a mixed flora of bacteria isolated from DUWLs, and the PVDF-coated tube was found to be effective in preventing biofilm formation using this model.

Effect of biocides on biofilm bacteria from dental unit water lines

Microbial biofilm formation in dental unit water lines (DUWL) is a phenomenon that has been recognized for nearly four decades. Water delivered by DUWL can harbor high numbers of bacteria, including opportunistic pathogens. Biofilms on tubing within DUWL may serve as a reservoir for these microorganisms and should therefore be controlled. In this study, the effects of eight biocides were monitored on DUWL biofilms individually and in combination by epifluorescence microscopy and total viable counts (TVC). The effects of sodium dodecyl sulphate (SDS), hydrogen peroxide (H2O2), sodium hypochlorite (NaOCl), phenol (Phe), Tween 20 (Tw 20), ethylenediaminetetraacetic acid (EDTA), chlorohexidine gluconate (CHX), and povidine iodine (PI) were tested on DUWL biofilms alone and in combination. PI was found to have negligible effects on biofilm removal either applied alone or in combined form with CHX. Applying all biocides simultaneously did not completely eliminate viable bacteria nor did they remove biofilm. Overall, when combined, the biocides performed better than singly applied products. The most effective biocides were NaOCl and Phe (both alone and in combination).

Comparison of the efficacies of disinfectants to control microbial contamination in dental unit water systems in general dental practices across the European Union

Water delivered by dental unit water systems (DUWS) in general dental practices can harbor high numbers of bacteria, including opportunistic pathogens. Biofilms on tubing within DUWS provide a reservoir for microorganisms and should be controlled. This study compared disinfection products for their ability to meet the American Dental Association's guideline of <200 CFU x ml(-1) for DUWS water. Alpron, BioBlue, Dentosept, Oxygenal, Sanosil, Sterilex Ultra, and Ster4Spray were tested in DUWS (n = 134) in Denmark, Germany, Greece, Ireland, The Netherlands, Spain, and the United Kingdom. Weekly water samples were tested for total viable counts (TVCs) on yeast extract agar, and, where possible, the effects of products on established biofilm (TVCs) were measured. A 4- to 5-week baseline measurement period was followed by 6 to 8 weeks of disinfection (intermittent or continuous product application). DUWS water TVCs before disinfection ranged from 0 to 5.41 log CFU x ml(-1). Disinfectants achieved reductions in the median water TVC ranging from 0.69 (Ster4Spray) to 3.11 (Dentosept) log CFU x ml(-1), although occasional high values (up to 4.88 log CFU x ml(-1)) occurred with all products. Before treatment, 64% of all baseline samples exceeded American Dental Association guidelines, compared to only 17% following commencement of treatment; where tested, biofilm TVCs were reduced to below detectable levels. The antimicrobial efficacies of products varied (e.g., 91% of water samples from DUWS treated with Dentosept or Oxygenal met American Dental Association guidelines, compared to 60% of those treated with Ster4Spray). Overall, the continuously applied products performed better than those applied intermittently. The most effective products were Dentosept and Oxygenal, although Dentosept gave the most consistent and sustained antimicrobial effect over time.

Inhibitory effect of PVDF tubes on biofilm formation in dental unit waterlines

OBJECTIVES

It has been reported that dental unit waterlines (DUWLs) are contaminated with bacterial biofilm, and that water discharged from a DUWL contains bacteria that might be opportunistic pathogens. This study aimed to investigate the ability of polyvinylidene fluoride (PVDF) tubing to inhibit bacterial contamination in DUWLs.

METHODS

Newly installed dental units were equipped with either a conventional polyurethane tube (unit A) or a PVDF tube (unit B), and the numbers of bacteria discharged from high- and low-speed handpiece lines were counted using R2A agar plates. Bacterial attachment on surfaces was observed with a scanning electron microscope (SEM) up to 185 days. Bacterial outflow during 1-day clinical service from a DUWL after 1-year usage was also examined. The surface free energy of each tube was determined based on the measurement of contact angles.

RESULTS

The number of bacteria discharged from unit B was lower than from unit A at 80 days and thereafter. SEM examination demonstrated that the unit A tube was covered by biofilm constituting rods and filaments after 94 days, while no biofilm was observed in the unit B tube even after 185 days. After 1-year of usage, the unit B released significantly less bacteria than the unit A at every sampling period of 1-day clinic work. Surface free energies, calculated from contact angles measured, of PVDF and polyurethane tubes were 37.7 and 77.8, respectively.

SIGNIFICANCE

The present results indicate that PVDF tubes, which have lower surface free energy than the conventional tubes, were effective in inhibiting biofilm formation and reducing bacterial outflow from DUWLs.

Recolonization of laser-ablated bacterial biofilm

The recolonization of laser-ablated bacterial monoculture biofilm was studied in the laboratory by using a flow-cytometer system. The marine biofilm-forming bacterium Pseudoalteromonas carrageenovora was used to develop biofilms on titanium coupons. Upon exposure to a low-power pulsed irradiation from an Nd:YAG laser, the coupons with biofilm were significantly reduced both in terms of total viable count (TVC) and area cover. The energy density used for a pulse of 5 ns was 0.1 J/cm(2) and the durations of irradiation exposure were 5 and 10 min. When placed in a flow of dilute ZoBell marine broth medium (10%) the laser-destructed bacterial film in a flow-cytometer showed significant recovery over a period of time. The flow of medium was regulated at 3.2 ml/min. The increase in area cover and TVC, however, was significantly less than that observed for nonirradiated control (t-test, P< 0.05). The coupons were observed for biofilm area cover and TVC at different intervals (3, 6, and 9 h) after irradiation. While the biofilm in the control coupon at the end of 9 h of exposure showed 95.6 +/- 4.1% cover, the 5- and 10-min irradiated samples after 9 h showed 60.3 +/- 6.5 and 37.4 +/- 12.1% area cover, respectively. The reduced rate of recolonization compared to control was thought be due to the lethal and sublethal impacts of laser irradiation on bacteria. This observation thus provided data on the online recolonization speed of biofilm, which is important when considering pulsed laser irradiation as an ablating technique of biofilm formation and removal in natural systems.

A between-patient disinfection method to control water line contamination and biofilm inside dental units

The aim of the present study was to evaluate the efficacy of a between-patient disinfection procedures to maintain low bacterial counts in dental unit water line (DUWL) effluents, and control dental water line biofilms. Six dental units already in use, that had never been cleaned, were monitored for three weeks. During the first week only baseline contamination levels were assessed with no treatment of the system. In the second week lines were flushed with water for 30 s before treating each patient. During the third week, a disinfection procedure with 0.26% peracetic acid, followed by a water flush, was implemented before treating each patient. DUWL samples were collected both at the beginning and at the end of 216 dental procedures (72 during each period), plated on R2A agar and incubated at room temperature for seven days to obtain total bacterial counts in colony forming units per millilitre. To assess biofilm control, nine dental units (five never used and four old dental units with established biofilm) were used for 30 days in routine dental practice undergoing five between-patient DUWL disinfecting cycles every day. Water line samples were removed at baseline and at the end of the study and examined by scanning electron microscopy to determine the presence or absence of biofilms. A significant difference (P < 0.01) in mean DUWL bacterial counts was found between the three sets of observations. Biofilms were not present in any of the new dental units and a demonstrable reduction in the biofilms from the four dental units with previous presence of established biofilms was observed at the end of the study. In this study, a between-patient disinfection procedure consisting of flushing DUWL with peracetic acid with use of water was efficacious in the control of both microbial contamination of dental treatment water and dental water line biofilms.

The effect of washing water on bonding to etched enamel

There is current concern about bacterial contamination of dental unit waterlines. This research hypothesized that the presence of increasing concentrations of bacteria in water used to wash etched enamel would result in a corresponding decrease in both shear bond strength (SBS) and critical surface tension (gammaC) of enamel. A further hypothesis was made that there is a correlation between SBS and gammaC. The effect of 3.5 ppm iodine in the water as a bacteriostatic agent was also assessed. Five groups of 10 samples of bovine enamel were etched, washed, and a resin composite bonded to them. The control group was washed with distilled water. Another group was washed with the dilute iodine solution. The remaining three groups used a different concentration of Escherichia coli DH5alpha as follows (in cfu mL(-1)): group 1: 10(2); group 2: 10(4); group 3: 10(6). Shear bond strength data were measured on an Instron testing machine at a crosshead speed of 1 mm min(-1). Adhesion data were (MPa): control: 24.6 +/- 6.0; with iodine: 20.8 +/- 2.7; group 1: 19.8 +/- 2.7; group 2: 13.5 +/- 3.0; group 3: 13.9 +/- 3.6. The F-test yielded a highly significant difference between control group, iodine group and group 1, compared with groups 2 and 3 (P < 0.0001). Tukey's Studentized Range Test was used for pairwise comparison testing between groups. Using a Cahn dynamic contact angle analyzer and linear regression analysis, the plots of surface tension versus costheta were extrapolated to costheta = 1 to give gammaC data for the control group and groups 1-3. In all cases reasonable linearity was observed (r2 > or = 0.87). Data (mN m(-1)) were: control group: 50.8; group 1: 45.1; group 2: 43.2; group 3: 39.5. The SBS and gammaC were then plotted against each other and linear regression analysis performed. It was concluded that increasing concentrations of bacteria in wash water decreased both SBS and gammaC and that a linear correlation (R2 = 0.84) was found between the values of these two parameters.

Decontamination of dental unit water systems with hydrogen peroxide

AIMS

Transmission of microbial pathogens to patients from water in dental units is a concern. To reduce this risk, the decontaminating efficiency of hydrogen peroxide was evaluated.

METHODS AND RESULTS

Three percent hydrogen peroxide diluted 1 : 4 in distilled water (contact time 15 min) was used daily to disinfect the waterlines of a pilot unit previously contaminated with Pseudomonas aeruginosa or Staphylococcus aureus. The behaviour of the test bacteria was seen to differ over time. Staph. aureus numbers slowly decreased until only low numbers were recovered, after which the levels remained stable. Ps. aeruginosa abatement was more rapid and the density of the bacteria reached a peak when the circuit was empty.

CONCLUSIONS

Staph. aureus and Ps. aeruginosa treated with hydrogen peroxide fell from 6 to 4 log.

SIGNIFICANCE AND IMPACT OF THE STUDY

Treatment of dental unit waterlines with hydrogen peroxide was seen to be able to keep the number of the bacteria under control, as long as the treatment was repeated daily.

Formation and Decontamination of Biofilms in Dental Unit Waterlines

BACKGROUND

Biofilms are a natural occurrence in aquatic environments, including community drinking water systems. The interior of small-diameter tubings in dental unit waterlines (DUWL) are also sites of biofilm formation. In the lumen of the tubings, the flow is minimal, and the water becomes stagnant when the units are not in use. Molecules precipitate from the water onto the interior wall and promote the adherence of planktonic microorganisms from the water. Once they become sessile, the microorganisms change their phenotype. After adherence, there is a so-called surface-associated lag time, and the organisms then enter a growth phase and produce exopolysaccharides that coat the organisms in a slime layer. Within the biofilm, the microorganisms can signal one another, transfer nutrients, and exchange genetic material. The insoluble exopolysaccharides shield the microorganisms from displacement and from penetration by predator organisms, antibiotics, and disinfectants. The external surface layer of microorganisms is faster growing and may detach as "swarmer" cells. Detachment of microorganisms from dental unit biofilm flushed into the oral cavity could theoretically infect the patient. Splatter and aerosols from dental procedures may possibly infect health care personnel.

METHODS

This study compared three DUWL cleaners (an alkaline peroxide product, a freshly mixed chlorine dioxide product, and a buffer-stabilized chlorine dioxide product) in 16 dental units with self-contained water systems, 6 months after installation in a periodontal teaching clinic. One unit treated by flushing and drying served as a control. Units were sampled daily for 10 days with heterotrophic plate count (HPC) sampler plates. The plates were incubated for 7 days at room temperature, and colonies were counted at 10.5x magnification. Samples of internal water tubing before and after the use of waterline cleaners were processed and examined by scanning electron microscopy.

RESULTS

The estimated mean HPC was derived from original and replicate independent counts of two investigators of undiluted and diluted samples, reported as colony forming units (CFU)/ml. Shock treatments with the alkaline peroxide product (n = 5) reduced the HPC from baseline, but in the ratio of daily counts to control, there was a large variance and a trend to return of high counts as days passed. The mean daily HPC was significantly better than the control for only 3 of the 9 days of treatment and exceeded the goal of 200 on 3 days. Freshly mixed chlorine dioxide (n = 4) and the buffer-stabilized chlorine dioxide (n = 5) both reduced HPC to near 0 on all days. Their ratios of daily estimated means to that of the control were significantly (P < 0.001) better at all times. In comparing treatments, the freshly mixed chlorine dioxide was better (P < 0.001) than the alkaline peroxide on 8 of 9 days. The buffered chlorine dioxide treatment was better than the alkaline peroxide at all times. The two chlorine dioxide treatments each had so many HPC counts of 0 that a meaningful statistical difference between them was not calculated. Scanning electron microscopy of plastic waterline tubing samples taken before and after treatments showed reductions in biofilm coverage, but the differences were not statistically significant.

CONCLUSIONS

Chlorine dioxide waterline cleaners are effective in decontaminating DUWL biofilm. Chlorine dioxide has advantages over other chlorine products. Controlling DUWL biofilm may have beneficial effects on nosocomial infections.

The effect of disinfectant agents in eliminating the contamination of dental unit water

High concentrations of water-borne organisms cause multiple public health problems. Contamination of water exiting the dental unit water lines could be inhibited with the use of some disinfectants. The purpose of this investigation was to establish the effect of two disinfectants and to test their capacity to eliminate colony forming units (CFU) per mL. Vacuum lines of four chairs were treated for a total of 2 weeks. Two disinfectants (Bio 2000 and Alpron) were used as per manufacturer's instructions. Water samples for hetereothrophic counts from each unit's air/water syringe line were collected before treating the first patient of the day. Baseline, daily, first and second week samples of 10 mL were plated on blood agar plates and eosin ethylene blue agar. For meosifilic bacterial counts, Mueller Hinton agar plates with 1 mL direct and 1/10 were used in sterile serum and CFU were counted. The suspected colonies were further evaluated using API 20E and API 20NE. No Gram(-) opportunistic pathogens were found during the entire observation. Baseline contamination level (>102 CFU mL-1) without use of disinfectants was significantly higher (P < 0.0001) than at both first and second weeks when disinfectants were used. No colony was formed when Bio 2000 was used after both first and second weeks, whereas small number of CFU mL-1 was found at the end of the first week when Alpron (<10) was used. In conclusion, when used daily, both disinfectants prevent the development of bacterial contamination after first and second weeks with no significant differences (P=0.35).

Efficacy of anti-retraction devices in preventing bacterial contamination of dental unit water lines

OBJECTIVE

In this study we examine the efficacy of anti-retraction devices in preventing microbial contamination of dental unit water lines (DUWLs).

METHODS

The study was performed on 54 randomly selected DUs in use at private and public institutions for over six months. The selected DUs were all currently commercially available. To evaluate the efficiency of anti-retraction devices, two different methods were employed, mechanical and microbiological. The ADA/ANSI specification #47 (corresponding to a water retraction of less than 40.3 microl) was used for the evaluation of the retraction determined using the mechanical method; the presence/absence of test microorganisms in DUWLs upstream the turbine after the test was used for evaluating the microbiological assay.

RESULTS

Both evaluation methods indicated correct amounts of retraction and prevention of DUWL contamination occurred in only two cases (3.7%). Correct retraction was noted in six other dental units (DUs), but their DUWLs became contaminated during testing. Six other produced the opposite results-improper retraction, yet no contamination. The remaining 40 DUs (74.0%) failed both evaluations.

CONCLUSION

The results showed that the overwhelming majority of the anti-retraction devices did not prevent retraction when the turbine stopped running, leading to a contamination of the water lines, and to a consequent possible cross-contamination of the patients.

The effect of a disinfectant/coolant irrigant on microbes isolated from dental unit water lines

The purpose of this study was to assess water samples from a hospital dental clinic to determine whether a disinfectant/coolant irrigant containing chlorhexidine (Lines, Micrylium Laboratories) affects the presence of microbial organisms in dental unit waterlines. Water samples from three hospital dental operatories were collected at baseline and after overnight treatment with a disinfectant-containing irrigant followed by sterile water irrigation. Saliva of treated patients and sterile water rinse specimens were collected from the waterlines of these operatories for three consecutive days, then weekly for eight weeks after treatment. Specimens were cultured to identify total heterotrophic plate counts as well as presence of Pseudomonas aeruginosa and Candida species. Baseline organism counts varied from 10(3) to 10(5) colony-forming units per milliliter. After treatment, no organisms were detected in waterline discharge. Decontamination of dental unit waterlines is possible using a disinfectant/irrigant followed by sterile water irrigation. The potential for contamination of the lines from patients' saliva may have been reduced due to use of anti-retraction valves and the disinfectant/sterile water irrigation, as conducted in this study.

The effects of prior growth as a biofilm on the virulence of Salmonella typhimurium for mice

Relatively little is known about how growth as a biofilm affects the virulence of pathogenic bacteria. In this study, the virulence of Salmonella typhimurium grown as a biofilm, or as planktonic cells, was compared in mice. Increased numbers of colony forming units were recovered from the spleens of mice 5 days after i.p. injection with S. typhimurium grown as a biofilm, as compared with planktonic cells (P < 0.05). No significant difference in the CFU of S. typhimurium recovered from the liver was noted at the same time point, and no difference was noted in the CFU recovered from the spleen or liver at 5 days after i.v. or i.g. inoculation with 10(5) S. typhimurium. Nor were any differences noted at 7 days after i.p., i.v. or i.g. inoculation. Thus, any effect of growth as a biofilm has on the virulence of S. typhimurium seems to be limited to the first 5 days after i.p. inoculation.

A new chemical formulation for control of dental unit water line contamination: An 'in vitro' and clinical 'study'

BACKGROUND: Water delivered by dental units during routine dental practice is highly contaminated. The aim of this study is to evaluate the efficacy of a new chemical solution flushed through Dental Unit Water Lines (DUWL) for the control of contamination inside dental units. MATERIALS AND METHODS: Six old dental units equipped with a device designed to automatically flush disinfecting solutions through the water system (Castellini Autosteril) were selected. Water samples from DUWL effluents were collected in each dental unit for 10 randomly selected days, before and after a 5 minute DUWL disinfecting cycle with TetraAcetylEthileneDiamine (TAED) and persalt (Ster4spray produced by Farmec spa, and distributed by Castellini spa). Water samples were plated in R2A Agar and cultured at room temperature for 7 days, and the total number of heterotrophic microorganisms counted and expressed in Log10 CFU/mL A general linear model was fitted and multiple regression ANOVA for repeated measures was used for the statistical analysis. RESULTS: The mean contamination in DUWL effluent at baseline was 5.45 &#PlusMinus; 0.35 CFU/mL (range 4.79 to 5.93 CFU/mL). When water samples were tested "in vitro" against the chemical, no growth of heterotrophic bacteria was detected after a 5 minute contact in any of the water samples tested. After undergoing a 5 minute disinfecting cycle with the chemical, DUWL mean contamination in water effluents was 2.01 &#PlusMinus; 0.32 CFU/mL (range 1.30 to 2.74 CFU/mL) (significant difference with respect to baseline). CONCLUSIONS: An inbetween patient disinfecting procedure consisting of flushing DUWL with TAED and persalt equivalent to 0.26% peracetic acid could be useful in routine dental practice for cross-contamination control.

Evaluation of ultrasonic scaling unit waterline contamination after use of chlorine dioxide mouthrinse lavage

BACKGROUND

An infection control problem in dental operatories which is not fully controlled is waterline contamination by heterotrophic mesophilic bacteria. These bacteria are present in water supplies as a planktonic phase and adhere to the lumen of tubings as a biofilm comprised of their external cell surface glycocalyx and by production of extracellular carbohydrate polymers. The adherent film is most difficult to remove. The accumulated planktonic phase can be reduced significantly by flushing water from the lines before use in patient treatment, but will return when the equipment is idle through the accumulation of more planktonic phase and by slough of the biofilm surface-adsorbed phase not yet enmeshed in the carbohydrate matrix. Chlorine dioxide has antimicrobial activity against many bacteria, spores, and viruses. It is used in water supply treatment as a disinfectant and slime preventive and has an advantage over chlorine in that carcinogenic trihalomethanes are not generated.

METHODS

This study compared use of phosphate buffer-stabilized chlorine dioxide (0.1%) mouthrinse as a lavage in ultrasonic dental scaler units with the use of tap water as a control. Sterile water flushed through the units onto heterotrophic plate count (HPC) sampler plates was cultured 7 days at room temperature and colonies were counted at 12x. One test and one control unit were used for biopsy of internal tubing and scanning electron microscopy imaging.

RESULTS

The HPC counts, in colony forming units (CFU)/ml, were reduced 3- to 5-fold by flushing tap water through the units, but they returned after units were idle overnight. When phosphate-buffered chlorine dioxide mouthrinse was used as a lavage, CFU/ml were reduced 12- to 20-fold. Holding chlorine dioxide in waterlines overnight reduced recurrent buildup compared to water (P <0.05). Scanning electron microscopy images indicated a significant reduction of biofilm coverage by chlorine dioxide as compared to water (P<0.001).

CONCLUSIONS

Phosphate-buffered chlorine dioxide mouthrinse was effective in these short-term trials for control of waterline contamination in ultrasonic dental scaling units. It should prove as useful in dental professional waterline applications as it has in industrial uses for biofilm control.

Microbial biofilm formation and contamination of dental-unit water systems in general dental practice

Dental-unit water systems (DUWS) harbor bacterial biofilms, which may serve as a haven for pathogens. The aim of this study was to investigate the microbial load of water from DUWS in general dental practices and the biofouling of DUWS tubing. Water and tube samples were taken from 55 dental surgeries in southwestern England. Contamination was determined by viable counts on environmentally selective, clinically selective, and pathogen-selective media, and biofouling was determined by using microscopic and image analysis techniques. Microbial loading ranged from 500 to 10(5) CFU. ml(-1); in 95% of DUWS water samples, it exceeded European Union drinking water guidelines and in 83% it exceeded American Dental Association DUWS standards. Among visible bacteria, 68% were viable by BacLight staining, but only 5% of this "viable by BacLight" fraction produced colonies on agar plates. Legionella pneumophila, Mycobacterium spp., Candida spp., and Pseudomonas spp. were detected in one, five, two, and nine different surgeries, respectively. Presumptive oral streptococci and Fusobacterium spp. were detected in four and one surgeries, respectively, suggesting back siphonage and failure of antiretraction devices. Hepatitis B virus was never detected. Decontamination strategies (5 of 55 surgeries) significantly reduced biofilm coverage but significantly increased microbial numbers in the water phase (in both cases, P < 0.05). Microbial loads were not significantly different in DUWS fed with soft, hard, deionized, or distilled water or in different DUWS (main, tank, or bottle fed). Microbiologically, no DUWS can be considered "cleaner" than others. DUWS deliver water to patients with microbial levels exceeding those considered safe for drinking water.