Microbial contamination of dental unit waterlines: the scientific argument

Mycobacteria in drinking water distribution systems: ecology and significance for human health

In contrast to the notorious pathogens Mycobacterium tuberculosis and M. leprae, the majority of the mycobacterial species described to date are generally not considered as obligate human pathogens. The natural reservoirs of these non-primary pathogenic mycobacteria include aquatic and terrestrial environments. Under certain circumstances, e.g., skin lesions, pulmonary or immune dysfunctions and chronic diseases, these environmental mycobacteria (EM) may cause disease. EM such as M. avium, M. kansasii, and M. xenopi have frequently been isolated from drinking water and hospital water distribution systems. Biofilm formation, amoeba-associated lifestyle, and resistance to chlorine have been recognized as important factors that contribute to the survival, colonization and persistence of EM in water distribution systems. Although the presence of EM in tap water has been linked to nosocomial infections and pseudo-infections, it remains unclear if these EM provide a health risk for immunocompromised people, in particular AIDS patients. In this regard, control strategies based on maintenance of an effective disinfectant residual and low concentration of nutrients have been proposed to keep EM numbers to a minimum in water distribution systems.

Microbiological evaluation of dental unit water systems in general dental practice in Europe

A range of opportunistic pathogens have been associated with dental unit water systems (DUWS), particularly in the biofilms that can line the tubing. This study therefore aimed to assess the microbiology of DUWS and biofilms in general dental practices across seven European countries, including the United Kingdom (UK), Ireland (IRL), Greece (GR), Spain (ES), Germany (D), Denmark (DK) and the Netherlands (NL). Water supplied by 51% of 237 dental unit water lines exceeded current American Dental Association recommendations of < or = 200 colony-forming units (CFU) ml(-1). Microbiological loading of the source waters was between 0 (Denmark, the Netherlands and Spain) and 4.67 (IRL) log CFU ml(-1); water line samples from the DUWS ranged from 1.52 (ES) to 2.79 (GR) log CFU ml(-1); and biofilm counts ranged from 1.49 (GR) to 3.22 (DK) log CFU.cm(-2). Opportunistic pathogens such as legionellae (DK and ES), including Legionella pneumophila SG1 (DK and GR), and Mycobacterium spp. (DK, NL, GR, D and ES) were recovered occasionally. Presumptive oral streptococci (ES and NL), oral anaerobes (GR), Candida spp. (UK, NL and ES) and blood (GR and IRL) were detected at relatively low frequencies, but their presence indicated a failure of the 3-in-1 antiretraction valve, leading to back siphonage of oral fluids into the water and biofilm phase. These findings confirm that a substantial proportion of DUWS have high levels of microbial contamination, irrespective of country, type of equipment and source water. The study emphasizes the need for effective mechanisms to reduce the microbial burden within DUWS, and highlights the risk of occupational exposure and cross-infection in general dental practice.

Isolation of non-tuberculosis mycobacteria in treated dental unit waterlines

OBJECTIVE

The purpose of the study was to investigate the presence of non-tuberculosis mycobacteria (NTM) in dental unit waterlines that were being routinely treated with an intermittent use waterline cleaner.

STUDY DESIGN

The study was conducted at a hospital dentistry clinic where immunocompromised patients are seen. Water samples from two lines on one of two dental units were taken before and after routine weekend chemical treatment. Sampling was repeated on two subsequent occasions, on the same unit, at three monthly intervals. Laboratory techniques included centrifugation and membrane filtration to detect small numbers of organisms.

RESULTS

Mycobacterium simiae was isolated from one of the four pre-treatment samples and from two of the four post-treatment samples. Mycobacterium mucogenicum was isolated from one of the four post-treatment samples.

CONCLUSIONS

This pilot study found that NTM were present in DUWLs that were being routinely treated with an intermittent use chemical cleaner. Practitioners are urged to understand the limitations of available DUWL treatments, and to consider the use of sterile water for non-surgical, as well as surgical, treatment of immunocompromised patients.

Bacterial biofilms: from the natural environment to infectious diseases

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

Total viable counts, ATP, and endotoxin levels as potential markers of microbial contamination of dental unit water systems

OBJECTIVES

To determine if either ATP or endotoxin concentrations in water supplied by dental unit water systems (DUWS) correlated with total viable counts (TVC), and therefore could be used as a rapid, chairside measure of levels of microbial contamination.

DESIGN

A prospective trial.

METHOD

Fifty-seven water samples were taken from the 'triple spray', air rotor and source water supplies from 25 dental units in eight practices. The samples were assayed for endotoxin concentration, total ATP and TVC. A pilot study was performed to assess the relationship between TVC and total cell counts, as determined by flow cytometry.

RESULTS

ATP concentrations ranged from 22 to 958 relative light units (RLU) and free endotoxin ranged from 25 to 600 EU ml(-1). TVC varied from not detected to 2.16 x 10(4) CFU ml(-1). The ATP method proved to be a simple and rapid method that could be used at the chairside. However, there was no correlation between ATP or endotoxin concentrations and TVC in DUWS. TVC generally underestimated the total cell count by 50 to 500 fold.

CONCLUSION

Half of the water samples from DUWS exceeded recommended levels of TVC. However, ATP and endotoxin concentrations in DUWS water samples did not correlate with these TVC data and therefore could not be recommended as an alternative assay to TVC for measuring bacterial contamination or for monitoring water treatment efficacy.

Ozone therapy for the treatment of dental caries

BACKGROUND

Dental caries is a bacterially mediated disease characterised by demineralisation of the tooth surface, which may lead to cavitation, discomfort, pain and eventual tooth loss. Ozone is toxic to certain bacteria in vitro and it has been suggested that delivering ozone into a carious lesion might reduce the number of cariogenic bacteria. This possibly could arrest the progress of the lesion and may, in the presence of fluoride, perhaps allow remineralisation to occur. This may in turn delay or prevent the need for traditional dental conservation by 'drilling and filling'.

OBJECTIVES

To assess whether ozone is effective in arresting or reversing the progression of dental caries.

SEARCH STRATEGY

We searched the Cochrane Oral Health Group's Trials Register (to 7 November 2003); Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library Issue 3, 2003); MEDLINE and PREMEDLINE (OVID, 1966 to November 2003); EMBASE (OVID, 1980 to November 2003); CINAHL (OVID, 1982 to November 2003); AMED (OVID, 1985 to November 2003). Quintessence was handsearched through 2002 and KaVo were contacted as manufacturers of the HealOzone apparatus for any additional published or unpublished trials.

SELECTION CRITERIA

Inclusion was assessed independently by at least two reviewers. Trials were only included if they met the following criteria: randomisation in a controlled trial; single surface in vivo carious lesion accessible to ozone application; clear allocation concealment; ozone application to the lesions in the intervention group; no such application of ozone in the control group; outcomes measured after at least 6 months.

DATA COLLECTION AND ANALYSIS

Reviewers independently extracted information in duplicate. A paucity of comparable data did not allow meta-analytic pooling of the included studies.

MAIN RESULTS

Three trials were included, with a combined total of 432 randomised lesions (137 participants). Forty-two conference papers, abstracts and posters were excluded (from an unknown number of studies). The risk of bias in all studies appeared high. The analyses of all three studies were conducted at the level of the lesion, which is not independent of the person, for this reason pooling of data was not appropriate or attempted. Individual studies showed inconsistent effects of ozone on caries, across different measures of caries progression or regression. Few secondary outcomes were reported, but one trial reported an absence of adverse events.

REVIEWERS' CONCLUSIONS

Given the high risk of bias in the available studies and lack of consistency between different outcome measures, there is no reliable evidence that application of ozone gas to the surface of decayed teeth stops or reverses the decay process. There is a fundamental need for more evidence of appropriate rigour and quality before the use of ozone can be accepted into mainstream primary dental care or can be considered a viable alternative to current methods for the management and treatment of dental caries.

Prevalence of legionella waterline contamination and Legionella pneumophila antibodies in general dental practitioners in London and rural Northern Ireland

OBJECTIVES

To determine the prevalence of legionellae in dental unit waterlines (DUWL) in general dental practices in London and rural Northern Ireland and whether the organism occurs at a high enough frequency and magnitude in DUWL to represent a threat to dentists' health.

MATERIALS AND METHOD

Two hundred and sixty six (166 London, 100 Northern Ireland) randomly selected dental surgeries were recruited. Standardised 250 ml water samples were taken from the DUWL and 1 litre samples from the surgery cold water tap to measure the prevalence of legionellae. The dentists provided a blood sample for legionella serology.

RESULTS

The prevalence of legionellae was very low (0.37%). Legionellae were not isolated from DUWL or surgery basin taps in Northern Ireland. Legionella spp were isolated from the DUWL and surgery basin of one practice in London and from the cold water supply of a further three practices. The prevalence of Legionella pneumophila antibodies was less than that seen in a comparable group of London blood donors.

CONCLUSION

The risk to dentists' health from potential exposure to legionellae in this cohort of dentists was very low and this was confirmed by the very low seroprevalence and antibody titres to legionella detected in the dentists.

The effect of Sterilex Ultra for disinfection of dental unit waterlines

AIM

To evaluate the effect of a disinfectant agent based on hydrogen peroxide (Sterilex Ultra, Sterilex Corporation, Maryland, USA) on the microbiological water quality in dental unit waterlines (DUWL).

SETTING

Six older dental units were disinfected with Sterilex Ultra and another six units with sodium hypochlorite. The results were compared to six non-disinfected units examined during a period without patient treatment.

OUTCOME MEASURE

The number of colony forming units of bacteria (cfu)/ml of water was determined according to European Standards on water quality.

DESIGN

The water quality was initially determined during a six week period, and subsequently in more detail for two weeks. Finally, the effect of prolonged administration of Sterilex Ultra was investigated for six weeks.

RESULTS

Instillation of Sterilex Ultra according to the recommendations of the manufacturer initially reduced the number of bacteria in DUWL to <10(2) cfu/ml. However, following daily, as well as prolonged administration of Sterilex Ultra a gradual recolonisation was observed resulting in bacterial numbers >10(4) cfu/ml in a number of units. Major differences between the number of cfu/ml in individual units were observed.

CONCLUSION

Neither daily nor extended administration of Sterilex Ultra was capable of maintaining an acceptable water quality in these older dental units.

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.

Microbiological evaluation of a range of disinfectant products to control mixed-species biofilm contamination in a laboratory model of a dental unit water system

Dental unit water system (DUWS) tubing harbors complex multispecies biofilms that are responsible for high microbial levels at the distal outlet. The aim of this study was to use an established biofilm laboratory model to simulate biofouling of DUWS to evaluate practical, cost-effective, and evidence-based methods of microbial decontamination. Reproducible biofilms were developed in the model over 14 days; decontamination was assessed using total viable counts (TVC) and microscopic-image analysis techniques to view the inner surface of tubing. Flushing did not reduce the biofilm coverage or TVC. Combizyme and ozone did not completely eliminate the viable bacteria (70 and 65% reduction in biofilm TVC, respectively), nor did they remove the biofilm (45 and 57% reduction in biofilm coverage, respectively). Chlorhexidine and Bio2000 (active agent: ethanol and chlorhexidine), Tegodor and Gigasept Rapid (aldehyde based), and Grotanol (hydroxide based) completely eliminated the TVC but did not completely remove biofilm (31, 53 33, 34, and 64.9% reduction of biofilm coverage, respectively). Other products including Grotanol Flussig (phenol based), Betadine (povidone-iodine based), Alpron (chlorite based), and the hydroxide-containing products Sporklenz, Sterilex Ultra, Dialox, Sterilox, Sanosil, Oxigenal, and Grotanat Bohrerbad resulted in a 100% reduction in the biofilm TVC and a >95% reduction in biofilm coverage. The study demonstrated that while many disinfectants achieve a sufficient reduction in TVC they may not necessarily remove unwanted biofilm from the tubing surfaces as tested in this laboratory-controlled biofilm model.

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).

The genetics of nontuberculous mycobacterial infection

The molecular aetiology of familial susceptibility to disseminated mycobacterial disease, usually involving weakly pathogenic strains of mycobacteria, has now been elucidated in more than 30 families. Mutations have been identified in five genes in the interleukin-12-dependent interferon-gamma pathway, highlighting the importance of this pathway in human mycobacterial immunity. Knowledge derived from the study of these rare patients contributes to our understanding of the immune response to common mycobacterial pathogens such as Mycobacterium tuberculosis and Mycobacterium leprae, which remain major public health problems globally. This knowledge can be applied to the rational development of novel therapies and vaccines for these important mycobacterial diseases.

Risk assessment of dental unit waterline contamination

Biofilms form rapidly on dental unit waterlines. The majority of the organisms in the biofilm are harmless environmental species, but some dental units may harbour opportunistic respiratory pathogens. This paper describes a risk assessment approach to analysing the hazard from biofilm organisms contaminating dental unit waterlines on the respiratory health of both the dental team and patients. The health risk from the respiratory pathogens Legionella spp, Mycobacterium spp and Pseudomonads was found to be low. Nevertheless, in order to satisfy water regulations and comply with health and safety legislation dentists should institute infection-control measures to maintain the dental unit water at the standard of less than 200 colony-forming units per ml of aerobic bacteria.

Occurrence of mycobacteria in water treatment lines and in water distribution systems

The frequency of recovery of atypical mycobacteria was estimated in two treatment plants providing drinking water to Paris, France, at some intermediate stages of treatment. The two plants use two different filtration processes, rapid and slow sand filtration. Our results suggest that slow sand filtration is more efficient for removing mycobacteria than rapid sand filtration. In addition, our results show that mycobacteria can colonize and grow on granular activated carbon and are able to enter distribution systems. We also investigated the frequency of recovery of mycobacteria in the water distribution system of Paris (outside buildings). The mycobacterial species isolated from the Paris drinking water distribution system are different from those isolated from the water leaving the treatment plants. Saprophytic mycobacteria (present in 41.3% of positive samples), potentially pathogenic mycobacteria (16.3%), and unidentifiable mycobacteria (54.8%) were isolated from 12 sites within the Paris water distribution system. Mycobacterium gordonae was preferentially recovered from treated surface water, whereas Mycobacterium nonchromogenicum was preferentially recovered from groundwater. No significant correlations were found among the presence of mycobacteria, the origin of water, and water temperature.

Effective control of dental chair unit waterline biofilm and marked reduction of bacterial contamination of output water using two peroxide-based disinfectants

Bacterial biofilm in dental unit waterlines (DUWs) is a widespread problem, and poses a potentially significant risk of infection to dental staff and patients, particularly those who are medically compromised or immunocompromised. The purpose of the present study was to investigate the level of bacterial contamination of dental chair unit output water in the Dublin Dental Hospital, and to investigate the efficacy of two hydrogen peroxide-based disinfectants in reducing bacterial loads to < or =200 cfu/mL as recommended by the American Dental Association. The chemical quality of dental chair unit input and output water was well within the limits recommended for potable water. Water supplied to the units yielded an average aerobic heterotrophic bacterial cell density of 184 cfu/mL. However, the corresponding density in output water was considerably higher; the average cell density in water from the three-in-one air/water syringes and cup fillers in 12 chairs was 8200 and 4300 cfu/mL, respectively. Dental unit water obtained from 18 separate reservoir-supplied units in general practices in the Dublin area yielded an average of 66000 cfu/mL. The bacterial species found were predominantly environmental organisms, which were also present at low levels in the input water. Some of the species identified (e.g., Burkholderia cepacia and Pseudomonas fluorescens) are known opportunistic pathogens. The capacity of two disinfectants, Sterilex Ultra and Sanosil, to reduce bacterial contamination to safe levels was compared. In a controlled study, once weekly overnight (15 h) disinfection using either agent reduced the bacterial density to below the American Dental Association recommended level of 200 cfu/mL. However, once disinfection ceased the bacterial loads increased to unacceptably high levels within three weeks. Electron microscopic analysis showed that both disinfectants markedly reduced biofilm in the DUWs, but the biofilm rapidly became extensive again when once weekly disinfection ceased. While both disinfectants were equally effective in lowering the bacterial counts to acceptable levels, Sterilex Ultra was associated with clogging of DUWs in some dental chair units after repeated usage, suggesting that Sanosil is a more suitable agent for routine use.

Chlorine disinfection of atypical mycobacteria isolated from a water distribution system

We studied the resistance of various mycobacteria isolated from a water distribution system to chlorine. Chlorine disinfection efficiency is expressed as the coefficient of lethality (liters per minute per milligram) as follows: Mycobacterium fortuitum (0.02) > M. chelonae (0.03) > M. gordonae (0.09) > M. aurum (0.19). For a C.t value (product of the disinfectant concentration and contact time) of 60 mg.min.liter(-1), frequently used in water treatment lines, chlorine disinfection inactivates over 4 log units of M. gordonae and 1.5 log units of M. fortuitum or M. chelonae. C.t values determined under similar conditions show that even the most susceptible species, M. aurum and M. gordonae, are 100 and 330 times more resistant to chlorine than Escherichia coli. We also investigated the effects of different parameters (medium, pH, and temperature) on chlorine disinfection in a chlorine-resistant M. gordonae model. Our experimental results follow the Arrhenius equation, allowing the inactivation rate to be predicted at different temperatures. Our results show that M. gordonae is more resistant to chlorine in low-nutrient media, such as those encountered in water, and that an increase in temperature (from 4 degrees C to 25 degrees C) and a decrease in pH result in better inactivation.

Microbial flora of root canal-treated teeth associated with asymptomatic periapical radiolucent lesions

This study aimed to investigate the composition of microflora in endodontically treated teeth associated with asymptomatic periapical lesions in southern Chinese patients. Twenty-four teeth which had received nonsurgical root canal treatment more than 4 years previously, and which presents an acceptable coronal restoration with a periapical radiolucent area, were re-treated nonsurgically. Bacteriological samples were obtained after removal of the old root canal filling. The samples were inoculated on enriched trypticase soy agar and four selective media for incubation at 37 degrees C in both a carbon dioxide-enriched atmosphere and anaerobically. Eighteen teeth that had received gutta-percha root canal fillings were grouped for analysis, 12 (66.7%) of which contained cultivable microorganisms. The total colony forming units per ml of transport medium ranged from 0 to 2.3 x 10(5). The number of bacterial genera recovered ranged between 0 and 6, with facultative gram-positive cocci being the most prevalent group of bacteria isolated. Facultative anaerobic bacteria were present in all, whereas strict anaerobic bacteria were found in 3 out of the 12 teeth with positive growth. The size of the periapical rarefaction did not show any relationship with the quantity of microorganisms recovered. Coagulase-negative staphylococci, streptococci and Pseudomonas aeruginosa were most frequently isolated in this group of patients. The possible origin of these organisms is discussed.

Bacterial aerosols in the dental clinic: a review

A number of sources of bacterial aerosols exist within and outside the dental clinic. The concentration of bacterial aerosols and splatters appears to be highest during dental procedures, especially those generated by some procedures such as ultrasonic scaling, or using a high speed drill. Several infectious diseases could be transmitted to staff and patients by airborne bacterial and other contaminants in the dental clinic. Air-conditioning and ventilation systems should be regularly maintained to reduce environmental contaminants and to prevent recirculation of bacterial aerosols. Pre-procedural rinsing by patients with mouthwashes as well as vacuum and electrostatic extraction of aerosols during dental procedures could also be employed. Dental staff should also consider appropriate immunizations and continue to use personal protective measures, which reduce contact with bacterial aerosols and splatters in the dental clinic.

Legionella: from environmental habitats to disease pathology, detection and control

Studies on Legionella show a continuum from environment to human disease. Legionellosis is caused by Legionella species acquired from environmental sources, principally water sources such as cooling towers, where Legionella grows intracellularly in protozoa within biofilms. Aquatic biofilms, which are widespread not only in nature, but also in medical and dental devices, are ecological niches in which Legionella survives and proliferates and the ultimate sources to which outbreaks of legionellosis can be traced. Invasion and intracellular replication of L. pneumophila within protozoa in the environment play a major role in the transmission of Legionnaires' disease. Protozoa provide the habitats for the environmental survival and reproduction of Legionella species. L. pneumophila proliferates intracellularly in various species of protozoa within vacuoles studded with ribosomes, as it also does within macrophages. Growth within protozoa enhances the environmental survival capability and the pathogenicity (virulence) of Legionella. The growth requirements of Legionella, the ability of Legionella to enter a viable non-culturable state, the association of Legionella with protozoa and the occurrence of Legionella within biofilms complicates the detection of Legionella and epidemiological investigations of legionellosis. Polymerase chain reaction (PCR) methods have been developed for the molecular detection of Legionella and used in environmental and epidemiological studies. Various physical and chemical disinfection methods have been developed to eliminate Legionella from environmental sources, but gaining control of Legionella in environmental waters, where they are protected from disinfection by growing within protozoa and biofilms, remains a challenge, and one that must be overcome in order to eliminate sporadic outbreaks of legionellosis.