Microbial biofilm formation in DUWS and their control using disinfectants

Initial waterline contamination by Pseudomonas aeruginosa in newly installed dental chairs

Water contamination in dental unit waterlines (DUWLs) is a potential source of healthcare-associated infection during dental care. The aim of this study was to evaluate the microbiological quality of DUWLs water from newly installed dental chairs in a French University Hospital. The microbiological quality of water from 24 new DUWLs initially disinfected by ICX Renew-prior to use of the dental units for patient treatment-was assessed for total culturable aerobic bacteria at 22°C and 36°C, Legionella sp., Pseudomonas aeruginosa, and total coliforms. Among the 24 samples analyzed, 21 were compliant with the water quality levels: 19 had no bacteria, and 2 contained only 4 and 1 CFU/mL for total culturable aerobic bacteria at 22°C and 36°C, respectively. Three samples were non-compliant due to contamination by P. aeruginosa (4, 2, and 2 CFU/100 mL). Controlling and preventing the microbiological contamination of DUWLs, especially by pathogenic bacteria, at the time of the installation of the new dental chairs are crucial to prevent healthcare-associated infection in dentistry.

IMPORTANCE

Dental unit waterlines (DUWLs) of new dental chairs may be contaminated before their first clinical use, so an initial shock disinfection is crucial at the time of their installation. The microbiological analyses are crucial to control the water quality of DUWLs before their first clinical use because their disinfection does not guarantee the elimination of all bacteria.

UV-C side-emitting optical fiber-based disinfection: a promising approach for infection control in tight channels

The growth of pathogenic bacteria in moist and wet surfaces and tubing of medically relevant devices results in serious infections in immunocompromised patients. In this study, we investigated and demonstrated the successful implementation of a UV-C side-emitting optical fiber in disinfecting medically relevant pathogenic bacteria (Pseudomonas aeruginosa and Methicillin-resistant Staphylococcus aureus [MRSA]) within tight channels of polytetrafluoroethylene (PTFE). PTFE is a commonly used material both in point-of-use (POU) water treatment technologies and medical devices (dental unit water line [DUWL], endoscope). For a 1-m-long PTFE channel, up to ≥6 log inactivation was achieved using a 1-m-long UV side-emitting optical fiber (SEOF) with continuous 16-h exposure of low UV-C radiation ranging from ~0.23 to ~29.30 μW/cm2. Furthermore, a linear model was used to calculate the inhibition zone constant (k`), which enables us to establish a correlation between UV dosage and the extent of inactivated surface area (cm2) for surface-bound Escherichia coli on a nutrient-rich medium. The k` value for an irradiance ranging from ~150 to ~271.50 μW/cm2 was calculated to be 0.564 ± 0.6 cm·cm2/mJ. This study demonstrated the efficacy of SEOFs for disinfection of medically relevant microorganisms present in medically and domestically relevant tight channels. The impact of the results in this study extends to the optimization of operational efficiency in pre-existing UV surface disinfection setups that currently operate at UV dosages exceeding the optimal levels.IMPORTANCEGermicidal UV radiation has gained global recognition for its effectiveness in water and surface disinfection. Recently, various works have illustrated the benefit of using UV-C side-emitting optical fibers (SEOFs) for the disinfection of tight polytetrafluoroethylene (PTFE) channels. This study now demonstrates its impact for disinfection of medically relevant organisms and introduces critical design calculations needed for its implementation. The flexible geometry and controlled emission of light in these UV-SEOFs make them ideal for light distribution in tight channels. Moreover, the results presented in this manuscript provide a novel framework that can be employed in various applications, addressing microbial contamination and the disinfection of tight channels.

Electrolysed oxidising water as a multi-purpose biocide in dental healthcare-A scoping review

OBJECTIVES

The objective of this scoping review was to map evidence of electrolysed oxidising water (EOW) as a biocide for dental applications of relevance to older people and identify research gaps.

BACKGROUND

EOW is an emerging, "green," and cost-effective biocide. There are no reviews on the landscape of EOW research as either an antiseptic or disinfectant in dental healthcare or its suitability for the oral healthcare of older people.

MATERIALS AND METHODS

The review follows the PRISMA Extension for Scoping Reviews (PRISMA-ScR) guidelines. Database searches (Google Scholar, PubMed, Web of Science, Ovid, Scopus and Science Direct) were undertaken using MESH terms and Boolean operators with no date restrictions, to identify full-text, original reports published in English-language peer-reviewed journals.

RESULTS

The search yielded 114 papers that met the inclusion/exclusion criteria. Dental applications of EOW include its use as an endodontic irrigant (39%); mouth rinse/surgical irrigant (21%); disinfectant for dental unit water lines (19%) and dental biomaterials (17%); and for antimicrobial efficacy, effects on oral tissues and on dental material properties. Most studies (83%) evaluated a single EOW formulation (acidic, moderately acidic or neutral) that was either generated at 'point-of-use' (POU; 72%), bottled ('ready-to-use', RTU; 24%) or from unspecified (3%) sources. Six reports evaluated storage-related parameters and 25 evaluated clinical applications; 89 were in vitro studies and one investigated the cost-effectiveness of POU EOW.

CONCLUSIONS

Neutral-pH, EOW is effective as an antimicrobial agent without deleterious effects on oral tissues. However, research on the impact of storage conditions, anti-Candida biofilm efficacy and mechanism of action against yeasts, long-term effects on denture materials and cost-effectiveness is required to establish the suitability of EOW as a multipurpose biocide for dental healthcare, including infection-control requirements relating to older people.

The consistent application of hydrogen peroxide controls biofilm growth and removes Vermamoeba vermiformis from multi-kingdom in-vitro dental unit water biofilms

The water systems inside a dental unit are known to be contaminated with a multi-kingdom biofilm encompassing bacteria, fungi, viruses and protozoa. Aerosolization of these micro-organisms can potentially create a health hazard for both dental staff and the patient. Very little is known on the efficacy of dental unit disinfection products against amoeba. In this study we have examined the effect of four different treatment regimens, with the hydrogen peroxide (H₂O₂) containing product Oxygenal, on an in-vitro multi-kingdom dental unit water system (DUWS) biofilm. The treatment efficacy was assessed in time using heterotrophic plate counts, the bacterial 16S rDNA, fungal 18S rDNA gene load and the number of genomic units for Legionella spp. the amoeba Vermamoeba vermiformis. The results indicated that a daily treatment of the DUWS with a low dose H₂O₂ (0.02% for 5 h), combined with a weekly shock dose (0.25% H₂O₂, 30 min) is necessary to reduce the heterotrophic plate count of a severely contaminated DUWS (>10⁶ CFU.mL^-1) to below 100 CFU.mL^-1. A daily treatment with a low dose hydrogen peroxide alone, is sufficient for the statistically significant reduction of the total amount of bacterial 16S rDNA gene, Legionella spp. and Vermamoeba vermiformis load (p < 0.005). Also shown is that even though hydrogen peroxide does not kill the trophozoite nor the cysts of V. vermiformis, it does however result in the detachment of the trophozoite form of this amoeba from the DUWS biofilm and hereby ultimately removing the amoeba from the system.

Dental unit waterline testing practices: an 11-Year retrospective study

OBJECTIVES

This retrospective study examined the dental unit waterline (DUWL) testing practices of Saskatchewan dental clinics over a period of 11 years, with an emphasis on their responses after identification of high microbial levels.

MATERIALS AND METHODS

Dental clinics (n = 137) aseptically collected samples of output water from their air/water syringes, handpieces, and ultrasonic scaler lines using Sigma-Aldrich® waterline test kits and delivered them to a quality assurance laboratory. Tests were incubated for seven days at room temperature, and those with heterotrophic plate counts > 500 CFU/mL were reported as failures. Statistical analyses were performed on a database containing 4,093 test results.

RESULTS

Participating clinics submitted an average of 11 DUWL tests per year. Overall, 21% of tests failed, and a moderate positive association (rs=.52, p < 0.001) was found between clinics' DUWL testing frequency and failure rate. Only 7% of failed DUWL tests were followed up by collection of a subsequent test within two weeks, of which 47% still exceeded the 500 CFU/mL threshold.

CONCLUSIONS

Our findings demonstrate an association between DUWL testing frequency and detection of unacceptable microbial levels, along with infrequent retesting and often-inadequate intervention after a failed test. This suggests the need for further efforts at the regulatory and educational levels to maintain adequate water quality during dental treatment.

CLINICAL RELEVANCE

Procedural water can become contaminated in DUWLs and endanger patients. Regular DUWL monitoring and evidence-based interventions to treat contaminated systems are necessary to safeguard patient health.

Occurrence and prevalence of Legionella species in dental chair units in Germany with a focus on risk factors

PURPOSE

Water-bearing instruments and treatments in dental units produce aerosols originating from the dental unit waterlines (DUWLs), which are often microbially contaminated. Particularly, the presence of Legionella mainly realized as aerosols leads to a risk of infection in patients and dental staff.

METHODS

Here, we record the general bacteriological status of DUWLs in Germany and investigated the prevalence of Legionella spp., with a focus on identification and occurrence of distinct species considering the various aspects of dental practice such as dental chair equipment, disinfection methods, and temperatures.

RESULTS

Out of 3789 water samples of 459 dental practices, collected in the years 2019 and 2020, 36.4% were Legionella positive with predominance of L. anisa (97.89%) identified by MALDI-TOF biotyping. L. pneumophila was detected very rarely. Risk factor analysis revealed that temperatures >20°C are a significant factor for increased Legionella colonization.

CONCLUSION

In order to minimize the risk of infection, routine monitoring of the water quality in dental chair units is recommended with regard to general microbiological loads and to the presence of Legionella as opportunistic pathogen as well as the regular application of routine disinfection procedures.

First water safety plan approach applied to a Dental Clinic complex: identification of new risk factors associated with Legionella and P. aeruginosa contamination, using a novel sampling, maintenance and management program

Dental unit waterlines (DUWLs) represent a complex environment able to promote microbial contamination, due to functional, mechanical and practical risk factors. According to a water safety plan approach, the main goal is to preserve the health of dentists, dental staff and patients. The aim of this study is to develop a DUWLs water safety plan that is able to support correct and effective maintenance and disinfection procedures. Three different water systems serve 60 dental chairs: (i) water that comes directly from municipal water (Type A), (ii) water supplied by municipal water and water bottles (Type B) and (iii) water supplied only via water bottles (Type C). For each type, Legionella and Pseudomonas aeruginosa contamination was studied, by applying a new sampling scheme, based on separate sampling from water bottles, cup filler and handpieces. Type B DUWL is the only type of DUWL contaminated by L. pneumophila (ST 59) and L. anisa (mean contamination: 608.33 ± 253.33 cfu/L) detected in cup filler and handpieces, as well as the high presence of P. aeruginosa (44.42 ± 13.25 cfu/100 mL). Two subsequent shock treatments and resampling procedures were performed by increasing disinfectant dosage and contact time and removing some DUWL components linked to biofilm growth in DUWLs. A significant reduction of contamination was obtained for both microorganisms (Legionella spp.: -100%, p < 0.001 and P. aeruginosa: -99.86%, p = 0.006). The sampling strategy proposed allows us to identify the source of contamination and better focus on the maintenance and disinfection procedures. DUWLs represent an environment that requires a multidisciplinary approach, combining the knowledge of all DUWL components to correct procedures that are able to preserve the health of personnel and patients, as well as guaranteeing DUWLs' safe functionality.

Immersion of debrided diabetic foot ulcer (DFU) tissue in electrochemically generated pH neutral hypochlorous acid significantly reduces the microbial bioburden: whole-genome sequencing of Staphylococcus aureus, the most prevalent species recovered

BACKGROUND

Diabetic foot ulcer infections (DFUIs) are the leading cause of lower limb amputations, mediated predominantly by Staphylococcus aureus. pH neutral electrochemically-generated hypochlorous acid (anolyte) is a non-toxic, microbiocidal agent with significant potential for wound disinfection.

AIMS

To investigate both the effectiveness of anolyte for microbial bioburden reduction in debrided ulcer tissues and the population of resident S. aureus.

METHODS

Fifty-one debrided tissues from 30 people with type II diabetes were aliquoted by wet weight and immersed in 1 or 10 ml volumes of anolyte (200 parts per million) or saline for three min. Microbial loads recovered were determined in colony forming units/g (CFU/g) of tissue following aerobic, anaerobic and staphylococcal-selective culture. Bacterial species were identified and 50 S. aureus isolates from 30 tissues underwent whole-genome sequencing (WGS).

FINDINGS

The ulcers were predominantly superficial, lacking signs of infection (39/51, 76.5%). Of the 42/51 saline-treated tissues yielding ≥10⁵ CFU/g, a microbial threshold reported to impede wound-healing, only 4/42 (9.5%) were clinically-diagnosed DFUIs. Microbial loads from anolyte-treated tissues were significantly lower than saline-treated tissues using 1 ml (1065-fold, 2.0 log) and 10 ml (8216-fold, 2.1 log) immersion volumes (p<0.0005). Staphylococcus aureus was the predominant species recovered (44/51, 86.3%) and 50 isolates underwent WGS. All were meticillin-susceptible and comprised 12 sequence types (STs), predominantly ST1, ST5 and ST15. Whole-genome multilocus sequence typing identified three clusters of closely related isolates from 10 patients indicating inter-patient transmission.

CONCLUSIONS

Short immersions of debrided ulcer tissue in anolyte significantly reduced microbial bioburden: a potential novel DFUI treatment.

Bacterial biofilm prevalence in dental unit waterlines: a systematic review and meta-analysis

BACKGROUNDS

Numerous studies have shown that dental unit water lines (DUWLs) are often contaminated by a wide range of micro-organisms (bacteria, fungi, protozoa) and various prevalence have been reported for it in previous studies. Therefore, this review study aims to describe the prevalence of bacterial biofilm contamination of DUWLs.

METHODS

This is a systematic review and meta-analysis in which the related keywords in different international databases, including Medline (via PubMed) and Scopus were searched. The retrieved studies were screened and the required data were extracted from the included studies. Three standard methods including American Dental Association (ADA), The Center for Disease Control and Prevention (CDC) and contaminated > 100 CFU/ml(C-100) standards were used to assess the bacterial biofilm contamination of DUWLs. All studies that calculated the prevalence of bacterial biofilm contamination of DUWLs, and English full-text studies were included in the meta-analysis. Studies that did not have relevant data or used unusual laboratory methods were excluded. Methodological risk of bias was assessed by a related checklist and finally, the data were pooled by fixed or random-effect models.

RESULTS

Seven hundred and thirty-six studies were identified and screened and 26 related studies were included in the meta-analysis. The oldest included study was published in 1976 and the most recent study was published in 2020. According to the ADA, CDC and C-100 standards, the prevalence of bacterial contamination was estimated to be 85.0% (95% confidence interval (CI): 66.0-94.0%), 77.0% (95%CI: 66.0-85.0%) and 69.0% (95%CI: 67.0-71.0%), respectively. The prevalence of Legionella Pneumophila and Pseudomonas Aeruginosa in DUWLs was estimated to be 12.0% (95%CI: 10.0-14.0%) and 8.0% (95%CI: 2.0-24.0%), respectively.

CONCLUSION

The results of this review study suggested a high prevalence of bacterial biofilm in DUWLs; therefore, the use of appropriate disinfecting protocol is recommended to reduce the prevalence of contamination and reduce the probable cross-infection.

Biofilm growth and microbial contamination of dental unit waterlines at Kuwait University dental center

Biofilm formation in dental unit waterlines and the resulting microbial contamination of the water in the system has become a significant problem. Contaminated water in the dental units is a major concern in dental clinics due to potential risk of causing infections particularly in elderly and immunocompromised patients. The aim of this study was at first to determine microbial contamination of the dental unit waterlines and then to study the efficacy of a comprehensive disinfection protocol on decreasing the microbial load. Water samples were collected before and after disinfection procedure from handpieces and water storage bottles from the dental units, a small 1-cm tubing was cut from each unit and subjected to microbiological culture on different growth media. Identification of the predominant species was achieved by 16S rRNA gene sequencing. Microbial growth was observed in samples collected from all dental units. Upon disinfection procedure, microbial contamination in the water samples and in the tubing surfaces was significantly reduced (P > 0.05). 16S rRNA gene sequencing revealed the presence of several species belonging to the genera Staphylococcus, Corynebacterium and Roseomonas, some of which are implicated in human infections. Aggravation of the biofilm growth on the tubing surfaces and the microbial contamination in the water can be effectively controlled by implementing appropriate and routine disinfection protocols. This may help protect the dental unit staff and the patients being exposed to the risk of infections.

The Application of Silver to Decontaminate Dental Unit Waterlines-a Systematic Review

The contamination of dental unit waterlines (DUWLs) is a major health concern since it can pose cross-infection risks among dental professionals and their patients. Silver is one of the widely used metals in medical fields due to its superior antimicrobial properties. Silver-based agents have been commercially available for the decontamination of dental unit water currently. This systematic review aims to examine the evidence supporting efficacy and safety of application of silver to decontaminate DUWLs. We performed a search of the peer-review literature of studies in six electronic databases using corresponding search terms. Eligibility was restricted to English-language studies exploring the application of silver to decontaminate dental unit water, e.g., silver-based disinfectants and silver-coated dental waterlines tubing. The search identified 148 articles, and 9 articles that met the criteria were synthesized with qualitative narrative analyses. We observed good evidence of antimicrobial efficacy of silver with hydrogen peroxide on diverse microorganism present in DUWLs. Furthermore, there is insufficient evidence on the application of silver nanoparticles (AgNPs) as an efficient material to control the biofilms in DUWLs. Post-treatment data of either the bactericidal and bacteriostatic effects of silver or AgNPs, especially the actual clinical efficacy of long-term application, are scarce. More high-quality research is needed to resolve the gap on the optimal dosage and treatment options required to control bacterial and biofilm in DUWLs with silver-containing materials.

Disinfection methods of dental unit waterlines contamination: a systematic review

Background. Severe contamination of dental unit waterlines was found in healthcare settings. The benefits of decontamination methods are controversial. The aim of this review was to systematically evaluate disinfection methods in contamination control of dental unit waterlines.Methods. The terms 'dental unit waterline(s) or DUWL(s) or dental unit water line(s)' were searched through PubMed, Cochrane Library, Embase, Web of Science and Scopusup to 31 May 2021. The DUWLs' output water was incubated on R2A agar at 20-28 °C for 5-7 days to evaluate heterotrophic mesophilic bacteria. The risk of bias was evaluated by a modified Newcastle-Ottawa quality assessment scale.Results. Eighteen papers from the literature were included. One study indicated that water supply played a crucial role in disinfecting DUWLs. Three studies indicated that flushing decreased bacteria counts but did not meet the American CDC standard (500 c.f.u. ml^-1). All chlorine- and peroxide-containing disinfectants except sodium hypochlorite in one of 15 studies as well as three mouthrinses and citrus botanical extract achieved the standard (≤500 c.f.u. ml^-1). The included studies were of low (1/18), moderate (6/18) and high (11/18) quality.Conclusion. Independent water reservoirs are recommended for disinfecting DUWLs using distilled water. Flushing DUWLs should be combined with disinfections. Nearly all the chlorine-, chlorhexidine- and peroxide-containing disinfectants, mouthrinses and citrus botanical extract meet the standard for disinfecting DUWLs. Alkaline peroxide would lead to tube blockage in the DUWLs. Regularly changing disinfectants can reduce the risk of occurrence of disinfectant-resistant strains of microbes.

The effectiveness of surface disinfectants and a micellic H2O2 based water disinfectant on Candida auris

BACKGROUND

As infection control faces new challenges from emerging, multidrug resistant strains of the yeast Candida auris, this study was conducted in order to examine the efficacy of hospital surface disinfectants and a new water disinfectant against C. auris biofilm forms.

METHODS

We tested four reference strains of C. auris (NCPF8971, NCPF8977, NCPF8984, DSM21092) and one C. albicans strain (ATCC10231) against disinfectants based on ethanol (ETH), quaternary ammonium (QAC), a combination of glutaraldehyde, quaternary ammonium and surfactant (ALD) and potassium peroxymonosulfate (PP) as well as 3.4% H₂O₂ and 4.25% H₂O₂ alone. In addition, a micellic-based formulation containing 17% v/v hydrogene peroxide disinfectant (mH₂O₂) was tested. The efficacy of the disinfectants was measured in a 96-well plate using tetrazolium salt reduction (XTT) and the log₁₀ reduction assay.

RESULTS

ETH and QAC displayed in clinically recommended concentrations more than 5log₁₀ reduction and more than 80% XTT activity reduction for all of the Candida biofilms and planktonic cells. Only biofilms of C. auris NCPF8984 were additionally sensitive to all remaining disinfectants. All tested C. auris biofilms were sensitive to PP disinfectant and showed more than 5log₁₀ reduction. However, the XTT assay showed a reduction of less than 80% for the PP disinfectant, indicating the presence of active but non-culturable cells. The 25% mH₂O₂ (corresponding to 4.25% H₂O₂) killed Candida biofilms after 1 minute.

Distinct Microbial Community of Accumulated Biofilm in Dental Unit Waterlines of Different Specialties

The contamination of dental unit waterlines (DUWLs) is a serious problem and directly affects the dental care. This study aims to explore the microbial community of biofilm in DUWL from different specialties and investigate the associated factors. A total of 36 biofilm samples from 18 DUWL of six specialties (i.e., prosthodontics, orthodontics, pediatrics, endodontics, oral surgery, and periodontics) at two time points (i.e., before and after daily dental practice) were collected with a novel method. Genomic DNA of samples was extracted, and then 16S ribosomal DNA (rDNA) (V3–V4 regions) and ITS2 gene were amplified and sequenced. Kruskal–Wallis and Wilcoxon rank test were adopted for statistical analysis. Microbial community with high diversity of bacteria (631 genera), fungi (193 genera), and viridiplantae was detected in the biofilm samples. Proteobacteria was the dominant bacteria (representing over 65.74–95.98% of the total sequences), and the dominant fungi was Ascomycota (93.9–99.3%). Microorganisms belonging to multiple genera involved in human diseases were detected including 25 genera of bacteria and eight genera of fungi, with relative abundance of six genera over 1% (i.e., Acinetobacter, Pseudomonas, Enterobacter, Aspergillus, Candida, and Penicillium). The biofilm microbiome may be influenced by the characteristics of dental specialty and routine work to some extent. The age of dental chair unit and overall number of patients had the strongest impact on the overall bacteria composition, and the effect of daily dental practices (associated with number of patients and dental specialty) on the fungi composition was the greatest. For the first time, biofilm in DUWL related to dental specialty was comprehensively evaluated, with more abundance of bacterial and fungal communities than in water samples. Biofilm accumulation with daily work and multiple kinds of opportunistic pathogen emphasized the infectious risk with dental care and the importance of biofilm control.

An Evaluation of Two Systems for the Management of the Microbiological Quality of Water in Dental Unit Waterlines: Hygowater® and IGN Calbénium®

Water in dental unit waterlines (DUWL) represents a risk for vulnerable patients if its microbiological quality is not controlled. The aim of this prospective study was to evaluate two systems for its management under real conditions: Hygowater® and IGN Calbenium®. Samples of the output water of DUWL were obtained for 5 previously contaminated units connected to Hygowater®, and 5 non-contaminated units connected to IGN Calbenium®, which was already effective for more than 1 year, as a control group. Samples were regularly collected up to 6 months after the implementation of Hygowater®, and were then cultured and analyzed. With IGN Calbenium®, except for a technical problem and a sample result in one unit at 6 months (Heterotrophic Plate Count (HPC) at 37 °C of 66 colony forming units (cfu)/mL), the results showed an absence of contamination. Hygowater® took a couple of weeks to be effective on initially contaminated DUWL (over 200 cfu/mL for all the units), then showed its efficacy for 2 months (HPC at 37 °C with a mean of 40.2 ufc/mL, and HPC at 22 °C with a mean of 0.2 ufc/mL). At 6 months, results were satisfactory for HPC at 22 °C (mean of 12 ufc/mL), but HPC at 37 °C gave non-satisfactory results for 4 of the 5 units (mean of 92.2 ufc/mL). Both systems have an effect on the microbiological quality of DUWL. IGN Calbenium® appears to be more reliable on a long-term basis.

Marine-Source Quorum Quenching Enzyme YtnP to Improve Hygiene Quality in Dental Units

Biofilm in dental unit water lines may pose a health risk to patients and dental practitioners. An AdiC-like quorum quenching enzyme, YtnP, was cloned from a deep-sea probiotic Bacillus velezensis, and heterologously expressed in E. coli to examine the application on the improvement of hygiene problems caused by biofilm infection of Pseudomonas aeruginosa in dental units. Pseudomonas bacteria were isolated from dental chair units and used to grow static biofilms in the laboratory. A water filter system was designed to test the antifouling activity of YtnP in Laboratory, to simulate the biofilm contamination on water filter in dental unit water lines. The results demonstrated that the enzyme of YtnP was able to degrade the N-acyl homoserine lactones, significantly inhibited the EPS generation, biofilm formation, and virulence factors production (pyocyanin and rhamnolipid) of P. aeruginosa, and was efficient on the antifouling against P. aeruginosa. The findings in this study indicated the possibility of YtnP as novel disinfectant reagent for hygiene treatment in dental units.

Failure to eradicate non-tuberculous mycobacteria upon disinfection of heater-cooler units: results of a microbiological investigation in northwestern Italy

BACKGROUND

Heater-cooler units (HCUs) used during cardiopulmonary bypass may become colonized with non-tuberculous mycobacteria (NTM), including Mycobacterium chimaera. Recently, a worldwide investigation conducted in hospitalized infected patients has detected M. chimaera in several Stockert 3T HCUs manufactured by LivaNova.

AIM

Microbiological surveillance on Stockert 3T (LivaNova) and Maquet HCU40 (Getinge) devices as well as an evaluation of the efficacy of their recommended decontamination protocols.

METHODS

A total of 308 water samples were collected from 29 HCUs: 264 samples were collected from 17 Stockert 3T HCUs and 44 samples from 12 Maquet HCU40 devices. Samples were tested for total viable counts (TVCs) at both 22 and 36°C, Pseudomonas aeruginosa, coliform bacteria, and NTM. The microbiological surveillance began in June 2017 and ran until October 2019.

FINDINGS

A total of 308 HCU water samples were analysed, 65.5% of which yielded NTM. The most frequently colonized device with NTM was the Stockert 3T (88.2%), with a frequency of positive samples of 59.5% (157/264). The Maquet HCU40 devices less frequently yielded NTM (33.3%), with a frequency of positive water samples of 13.6% (6/44). Disinfection procedures were effective in reducing TVCs of bacteria with the exception of NTM species. NTM were detected in both pre-disinfection (50.1%) and post-disinfection (55.7%) samples, and no significant association was found between disinfection and NTM results both in Stockert 3T and Maquet HCU40 devices.

CONCLUSION

This study suggests that manufacturers' procedures for disinfection are ineffective and/or inadequate. Until effective disinfection protocols become available, the only way to minimize the risk of NTM contamination is to closely monitor the water quality in the HCU, keep it as clean as possible, and treat it like any other biohazardous material.

Microbial Contamination of Dental Unit Waterlines and Potential Risk of Infection: A Narrative Review

Several studies have revealed that dental unit waterlines (DUWLs) are often contaminated by large numbers of various micro-organisms (bacteria, fungi, protozoa, viruses). Microbial contamination in DUWLs may originate from the mains water piped into the dental unit, the suck-back of patients' saliva into the line due to the lack of adequate valves, and contamination from bottled water systems. Some of the main determinants of microbial contamination in DUWLs are: a very small lumen size (0.5-2 mm) of the tubing used, high surface-to-volume ratio (6:1), low throughput and the materials of which the tubing is made, water stagnation outside of working hours. The environmental conditions present inside the conduits of the dental unit may facilitate the proliferation of micro-organisms and the consequent formation of biofilm on the interior surface of the pipes of DUWLs. During the use of handpieces, particularly high-speed rotating instruments, a spray is thrown up in the form of aerosols or spatters containing biological material (saliva, blood and dental plaque) and micro-organisms. This means that the health of both dental staff and patients could be at risk of infection. The risk of cross-infections in dental settings can be tackled by implementing combined interventions to prevent the contamination of DUWLs.

Chlorine-based DUWL disinfectant leads to a different microbial composition of water derived biofilms compared to H2O2-based chemical disinfectants in vitro

Background

Biofilm formation in dental unit waterlines (DUWL) may lead to health risks for dental staff and patients. Therefore, dental unit waterlines need to be disinfected, for instance by using chemical disinfectants. However, the application of chemical disinfectants may lead to the selection of specific microorganisms. Therefore, the aim of our study was to assess the microbial composition of water-derived biofilms, after a continuous exposure to maintenance doses of commercially available chemical disinfectants, in vitro.

Methods

The AAA-model was used to grow water derived biofilms. The biofilms were subjected to the maintenance dose of each disinfectant. To determine the microbial composition, the V4 hypervariable region of the 16S rRNA gene was sequenced. The sequences were clustered in operational taxonomic units (OTUs).

Results

The bacterial composition of biofilms in all treatment groups differed significantly (PERMANOVA F = 4.441, p = 0.001). Pairwise comparisons revealed Anoxyl treated biofilms were significantly different from all groups (p = 0.0001). In the Anoxyl-treated biofilms, the relative abundance of Comamonadaceae and Sphingopyxis was high compared to the Dentosept, Green and Clean and Oxygenal groups.

Conclusion

We concluded that exposure to low doses of the chlorine-based chemical disinfectant Anoxyl led to a substantially different composition of water derived biofilms compared to biofilms exposed to H₂O₂-based chemical disinfectants.

Heterogeneity in the efficacy of dental chemical disinfectants on water-derived biofilms in vitro

Conditions in dental unit waterlines are favourable for biofilm growth and contamination of dental unit water. The aim of this study was to assess the effect of several chemical disinfectants on bacteria in a biofilm model. Water-derived biofilms were grown in a static biofilm model (Amsterdam Active Attachment model), using two growth media. Biofilms were challenged with Alpron/Bilpron, Anoxyl, Citrisil, Dentosept, Green & Clean, ICX and Oxygenal in shock dose and maintenance doses. The concentration and the composition of the chemical disinfectants influenced the number of culturable bacteria in the biofilms. The application of a single shock dose followed by a low dose of the same chemical disinfectants resulted in the greatest suppression of viable bacteria in the biofilms. Exposure to Citrisil and ICX consistently resulted in failure to control the biofilms, while Alpron/Bilpron had a substantial and relevant effect on the number of bacteria in the biofilms.

Efficacy of BRS® and Alpron®/Bilpron® Disinfectants for Dental Unit Waterlines: A Six-Year Study

Biofilms in dental unit waterlines (DUWL) are a potentially significant source of contamination posing a significant health risk as these may come into contact with patients and dental staff during treatment. The aim of this study was to evaluate the microbiological quality of DUWL water treated by Biofilm-Removing-System^® (BRS^®) and Alpron^®/Bilpron^® disinfectant solutions for six years in a French university hospital. The microbiological quality of water supplied by 68 dental units—initially shock treated with BRS^®, then continuously treated by Alpron^® with sterile water during working days and Bilpron^® during inactivity period, and combined with purging every morning and after each patient—was assessed biannually during six years for total culturable aerobic bacteria at 22 °C and 36 °C, Legionella sp., Pseudomonas aeruginosa, and total coliforms. A total of 628 samples were analyzed, 99.8% were compliant with extended microbiological levels, and we never detected pathogen bacteria like Legionella sp. and P. aeruginosa. Only one sample (0.2%) was noncompliant with the level of total culturable aerobic bacteria at 36 °C, which exceeded 140 colony forming units per mL. The protocol implemented in our university hospital gives excellent results and enables control of the microbiological quality of DUWL water in the long term.

Suction Hoses of Dental Units as a Potential Source of Microbial Contamination

OBJECTIVES

Dental units are necessary tools for modern dentistry. Microbial contamination of dental units is thought to be the result of biofilm formation in various parts of the unit. We aimed to identify the total microbial count in the suction hose of dental units, and detect the presence of Pseudomonas aeruginosa.

METHODS

Random sampling of suction hoses of dental units in Birjand, Iran, was performed in dental clinics on the first (n = 115) and last (n = 115) working days of the week. Total viable counts of bacteria and detection of P. aeruginosa were performed on plate count agar and cetrimide agar, respectively. Plates were incubated at 37 °C for 48 hours.

RESULTS

None of the samples were free from bacterial contamination. P. aeruginosa was detected in 22.6% and 18.3% of samples taken on the first and last working days, respectively.

CONCLUSIONS

Suction hoses were heavily contaminated with bacteria, especially opportunistic pathogens, and current disinfection does not adequately control the contamination.

Dental Unit Waterlines: A Survey of Practices in Eastern France

Water is essential during dental care. Physical and chemical techniques should be used to maintain a good water quality with respect to bacteria, and to ensure the safety of exposed patients and dental staff. The aim of this survey was to assess the modalities used by dental practitioners in Eastern France to maintain the water quality of their dental unit waterlines (DUWLs). A questionnaire about water quality maintenance practices was sent to 870 dental offices in 2016. The questionnaires were completed by 153 dental offices, covering about 223 dental care units. The majority of units were fed by mains water (91.0%), which is generally unfiltered (71.3%). One-third (33.6%) of the units had an independent water bottle reservoir. Flushing, a basic physical technique to improve the quality of units' outflow water, was practiced in 65.4% of dental offices. Concerning the chemical treatment of water, it was used for 62.1% of the units. An analysis of the microbiological quality of the DUWL water was only carried out in 2.6% of the offices. In conclusion, providing better training to dental staff seems necessary to improve their practices and to generalize procedures that improve the microbiological quality of the water used.

Colonization by Pseudomonas aeruginosa of dental unit waterlines and its relationship with other bacteria: suggestions for microbiological monitoring

Pseudomonas aeruginosa is an environmental bacterium, ubiquitous in aquatic habitats and water distribution systems, including dental unit waterlines (DUWLs). We investigated the prevalence of P. aeruginosa in DUWLs from private dental settings. We also analyzed the relationship between P. aeruginosa contamination and the presence of Legionella spp. and total viable count (TVC) in order to suggest a simple and inexpensive protocol to test the quality of water from DUWLs. We detected and quantified P. aeruginosa both by culture and by a PMA (propidium monoazide)-qPCR method. Overall, we detected P. aeruginosa in 17 samples using the PMA-qPCR and in 11 samples using the culture. All culture-positive samples were positive with the PMA-qPCR too, with an agreement between the two methods of 93% and a Cohen's kappa coefficient of κ = 0.747 (good concordance). Comparing results with results of our previous study, we noted that (a) P. aeruginosa was isolated only from DUWLs with high TVC and (b) five out of six Legionella-positive samples were negative for Pseudomonas spp. Our final suggestion is that the cleanliness of DUWLs should be assessed by TVC because it is a good indicator of the presence of pathogens such as Legionella spp. and P. aeruginosa.

Evaluation of Microbiological and Free-Living Protozoa Contamination in Dental Unit Waterlines

Studies conducted over the last 40 years have demonstrated that the water output from dental unit waterlines (DUWLs) is often contaminated with high densities of microorganisms. It has been monitored the microbiological quality of the water in 30 public dental facilities in northern Italy in order to assess the health risk for patients and dental staff. In each facility, samples of water both from taps and from DUWLs were analyzed in order to evaluate heterotrophic plate counts (HPCs) at 22 °C and 36 °C, and to detect coliform bacteria, Pseudomonas aeruginosa, Legionella pneumophila and amoebae. In 100% of the samples taken from the DUWLs, the concentration of HPCs was above the threshold as determined by the Ministère de la Santé et des Solidarités (2007). The concentration of P. aeruginosa was greater than the indicated threshold in 16.67% of the hand-pieces analyzed. A total of 78.33% of samples were contaminated by L. pneumophila, while in the samples taken from the DUWLs alone, this percentage rose to 86.67%. Amoebae were detected in 60% of the samples taken from hand-pieces; all belonging to the species V. vermiformis. This study documented the presence of various microorganisms, including Legionella spp., at considerably higher concentrations in water samples from DUWLs than in samples of tap water in the same facilities, confirming the role of the internal DUWLs in increasing microbial contamination, especially in the absence of proper management of waterborne health risks.

Different Trends in Microbial Contamination between Two Types of Microfiltered Water Dispensers: From Risk Analysis to Consumer Health Preservation

The use of microfiltered water dispensers (MWDs) for treatment of municipal water is increasing rapidly, however, the water quality produced by MWDs has not been widely investigated. In this work a large-scale microbiological investigation was conducted on 46 MWDs. In accordance with Italian regulations for drinking water, we investigated the heterotrophic plate counts at 36 and 22 °C for indicator bacteria and pathogenic bacteria, such as Enterococci, Pseudomonas aeruginosa, Escherichia coli and Staphylococcus aureus. Two different MWDs were compared: Type A with Ag⁺ coated carbon filter and two ultraviolet (UV) lamps, and Type B with a carbon filter and one UV lamp. For each type, the contamination of the input and output points was analyzed. Our findings showed that MWDs are a source of bacteria growth, with output being more contaminated than the input point. Type B was widely contaminated for all parameters tested in both sampling points, suggesting that water treatment by Type A is more effective in controlling bacterial contamination. MWDs are critical devices for water treatment in term of technologies, intended use, and sanitization procedures. The adoption of an appropriate drinking water safety plan associated with clear maintenance procedures and periodic environmental monitoring can ensure the safe and healthy operation of these devices.

The role of chemical products at low doses in preventing the proliferation of bacteria in dental unit waterlines: the ICX® experience

In this study we evaluated (1) the efficacy of a protocol that combines hydrogen peroxide (shock treatment) and ICX^® tablets (continuous treatment) for the control of microbial contamination in dental unit water lines, and (2) the in vitro antimicrobial activity of ICX^® tablets on collection and wild strains isolated from dental chair output waters. To assess the treatment effectiveness, the microbial load in the output water samples of three dental chairs were investigated: one control chair received only shock treatment. In vitro bactericidal activity was tested against Staphylococcus aureus and Pseudomonas aeruginosa. Data obtained from samples collected from chairs treated with ICX^® and shock treatment and data from the control chair did not differ significantly on the basis of microbial load. In the in vitro study, the product was unable to kill Gram-negative bacteria. These results show that the continuous introduction of ICX^® was not effective in maintaining low counts of the heterotrophic bacteria in the output water of dental devices, and shock treatment may be needed more frequently than monthly.

Dental Unit Water Lines and their Disinfection and Management: A Review

The perceived threat to public health from dental unit water line (DUWL) contamination comes from opportunistic and respiratory pathogens such as Legionella spp, Nontuberculous Mycobacteria (NTM) and pseudomonads. These organisms can grow and multiply in the DUWL biofilm to reach infective concentrations, with the potential for inhalation leading to respiratory infections or direct contamination of surgical wounds. In this paper we discuss current legislation and practical methods for delivering water within the DUWL that meets the standards for safety. Clinical relevance: Understanding the clinical relevance and methods for decontaminating DUWL is essential to create a safe working environment in dentistry.

Establishing a laboratory model of dental unit waterlines bacterial biofilms using a CDC biofilm reactor

In this study, a laboratory model to reproduce dental unit waterline (DUWL) biofilms was developed using a CDC biofilm reactor (CBR). Bacteria obtained from DUWLs were filtered and cultured in Reasoner's 2A (R2A) for 10 days, and were subsequently stored at -70°C. This stock was cultivated on R2A in batch mode. After culturing for five days, the bacteria were inoculated into the CBR. Biofilms were grown on polyurethane tubing for four days. Biofilm accumulation and thickness was 1.3 × 10⁵ CFU cm^-2 and 10-14 μm respectively, after four days. Bacteria in the biofilms included cocci and rods of short and medium lengths. In addition, 38 bacterial genera were detected in biofilms. In this study, the suitability and reproducibility of the CBR model for DUWL biofilm formation were demonstrated. The model provides a foundation for the development of bacterial control methods for DUWLs.

Occurrence and diversity of both bacterial and fungal communities in dental unit waterlines subjected to disinfectants

Chemical disinfectants are widely advocated to reduce the microbial contamination in dental unit waterlines (DUWL). However, until now their efficacy has been poorly examined after long-term application. In this study, through quantitative PCR and high-throughput sequencing, both bacterial and fungal communities were profiled from 8- to 12-year-old DUWL treated with disinfectants commonly used by European dentists. Water was collected from the tap water supplying units to the output exposure point of the turbine handpiece following a stagnation period and dental care activity. Results showed that (i) the unit itself is the principal source of microbial contamination and (ii) water stagnation, DU maintenance practices and quality of water supplying DU appeared as parameters driving the water quality. Despite disinfecting treatment combined to flushing process, the microbial contamination remained relevant in the studied output water, in association with a high bacterial and fungal diversity. The occurrence of potentially pathogenic microorganisms in these treated DUWL demonstrated a potential infectious risk for both patients and dental staff. A disinfectant shock before a prolonged stagnation period could limit the microbial proliferation inside DUWL. Necessity to proceed to regular water quality control of DUWL was highlighted.

The efficacy of disinfectants in the decontamination of dental unit water lines: an in vitro laboratory study

Objectives/Aims:

This in vitro laboratory study compared the efficacy of water, sodium percarbonate (SPC) and chlorine dioxide (ClO₂) solutions in the disinfection of dental unit water lines (DUWLs).

Materials and Methods:

New DUWL tubes were cut, split open, and mono-culture and mixed-culture biofilms of Staphylococcus aureus, Enterococcus faecalis and Streptococcus mutans were grown. Harvested biofilms from the sectioned DUWL tubes were exposed to sterile distilled water, SPC or 5 and 10 p.p.m. ClO₂ in both a stationary phase and through a constant flow. Bacterial counts were compared using the Kruskal–Wallis nonparametric rank test.

Results:

In the mono-culture biofilms, SPC, 5 and 10 p.p.m. ClO₂ significantly reduced all the test organisms (P<0.01). However, no significant difference was found between SPC and ClO₂. In the mixed-culture biofilms exposed to disinfectant without flow, ClO₂ significantly reduced the biofilm (P=0.02) compared with water and SPC. Similarly, in the constant flow study, ClO₂ proved to be superior to water.

Conclusion:

At low concentrations, ClO₂ with and without flow significantly reduced the mixed-culture biofilm grown in vitro on the sections of the DUWL tubes. Therefore, it has the potential to be used in the patient treatment water, as it is potable at these concentrations, and to decontaminate and limit the biofilm formation in the water lines.

Quality of Drinking Water Treated at Point of Use in Residential Healthcare Facilities for the Elderly

Municipal tap water is increasingly treated at the point of use (POU) to improve the acceptability and palatability of its taste. The aim of this study was to assess the bacteriologic and nutritional characteristics of tap water treated at the point of use in residential healthcare facilities for the elderly. Two types of POU devices were used: microfiltered water dispensers (MWDs) and reverse-osmosis water dispensers (ROWDs). All samples of water entering the devices and leaving them were tested for the bacteriological parameters set by Italian regulations for drinking water and for opportunistic pathogens associated with various infections in healthcare settings; in addition, the degree of mineralization of the water was assessed. The results revealed widespread bacterial contamination in the POU treatment devices, particularly from potentially pathogenic species. As expected, the use of ROWDs led to a decrease in the saline content of the water. In conclusion, the use of POU treatment in healthcare facilities for the elderly can be considered advisable only if the devices are constantly and carefully maintained.

Monitoring the decontamination efficacy of the novel Poseidon-S disinfectant system in dental unit water lines

BACKGROUND

Contaminated dental unit waterlines (DUWLs) are a known source of specific health care-acquired infections because of the difficulty in keeping them clean during routine dental practice. Recently, an electrolysis apparatus that uses only the chlorine normally present in municipal water, the Poseidon-S system, was developed as a novel additive-free disinfectant system to control microbial contamination in DUWLs.

METHODS

The microbiological quality of water samples collected from DUWLs was assessed before and after installation of the Poseidon-S system in terms of the total viable counts (TVCs) of microorganisms. The microbicidal effects of the electrolyzed water against oral organisms and its cytotoxicity against human oral-derived cell lines were also examined.

RESULTS

Water samples from the DUWLs initially had average microbial TVCs of 10³-10⁶ colony-forming units (CFU)/mL. After installation of the Poseidon-S system, the number of microorganisms in the water samples decreased to less than 1 × 10² CFU/mL. The electrolyzed water also exhibited remarkable microbicidal effects on the microorganisms present in the DUWLs as well as microorganisms commonly isolated from human oral cavities, but showed low cytotoxicity towards human oral-derived cells.

CONCLUSION

This study demonstrated that routine use of the Poseidon-S system can effectively maintain low microbial levels in DUWLs.

Biofouling of surgical power tools during routine use

Surgical power tools (SPTs) are frequently used in many surgical specialties such as dentistry, orthopaedics, ophthalmology, neurology, and podiatry. They have complex designs that may restrict access to cleaning and sterilization agents and frequently become contaminated with microbial and tissue residues following use. Due to these challenges, surgical power tools can be considered the weak link in the decontamination cycle and present a potential for iatrogenic transmission of infection. We aimed to review the existing literature on the decontamination of surgical power tools and associated iatrogenic transmission of infection. A search of the medical literature was performed using Ovid online using the following databases: Ovid Medline 1950-2014, Embase 1980-2014, and EBM Reviews Full Text--Cochrane DSR, ACP Journal Club, and Dare. Despite challenges to decontamination processes, reported episodes of iatrogenic infection directly linked to SPTs appear rare. This may reflect a true picture but more likely represents incomplete reporting, failure to investigate power tools, or lack of surveillance linking surgical site infections (SSIs) to power tools. Healthcare professionals should be aware of the complexities associated with the decontamination of different SPTs, and should review manufacturers' reprocessing instructions prior to purchase. More clarity is required in the manufacturers' validation of these reprocessing instructions. This particularly applies to the emerging surgical robot systems that present extreme challenges to decontamination between uses. Investigation of cross-infection incidents or SSI surveillance should include an element of assessment of SPT decontamination to further elucidate the contribution of SPTs to skin and soft tissue infections.

Impact of a risk management plan on Legionella contamination of dental unit water

The study aimed to assess the prevalence of Legionella spp. in dental unit waterlines of a dental clinic and to verify whether the microbiological parameters used as indicators of water quality were correlated with Legionella contamination. A risk management plan was subsequently implemented in the dental health care setting, in order to verify whether the adopted disinfection protocols were effective in preventing Legionella colonization. The water delivered from syringes and turbines of 63 dental units operating in a dental clinic, was monitored for counts of the heterotrophic bacteria P. aeruginosa and Legionella spp. (22 °C and 37 °C). At baseline, output water from dental units continuously treated with disinfection products was more compliant with the recommended standards than untreated and periodically treated water. However, continuous disinfection was still not able to prevent contamination by Legionella and P. aeruginosa. Legionella was isolated from 36.4%, 24.3% and 53.3% of samples from untreated, periodically and continuously treated waterlines, respectively. The standard microbiological parameters used as indicators of water quality proved to be unreliable as predictors of the presence of Legionella, whose source was identified as the tap water used to supply the dental units. The adoption of control measures, including the use of deionized water in supplying the dental unit waterlines and the application of a combined protocol of continuous and periodic disinfection, with different active products for the different devices, resulted in good control of Legionella contamination. The efficacy of the measures adopted was mainly linked to the strict adherence to the planned protocols, which placed particular stress on staff training and ongoing environmental monitoring.

Detection of oral streptococci in dental unit water lines after therapy with air turbine handpiece: biological fluid retraction more frequent than expected

AIM

Oral streptococci detected in water from dental unit water lines (DUWLs) are a surrogate marker of patients' biological fluid retraction during therapy. We investigated oral streptococci detection rate in DUWLs in a representative sample of private offices in real-life conditions.

MATERIALS & METHODS

Samples of nondisinfected water (100 ml) were collected from the DUWL designated for the air turbine handpiece in 81 dental units, immediately after dental treatment of patients with extensive air turbine handpiece use. Water was filtered and plated on a selective medium for oral streptococci and, morphologically, typical colonies of oral streptococci were counted. The lowest detection limit was 0.01 CFU/ml.

RESULTS

The oral streptococci detection rate was 72% (95% CI: 62-81%), with a mean level of 0.7 CFU/ml. Oral streptococci detection was not affected by handpiece age or dental treatment type, but was associated with dental unit age.

CONCLUSION

Biological fluid retraction into DUWLs during patient treatment and, possibly, the risk for patient-to-patient blood- or air-borne pathogen transmission are more frequent than expected.

Microbial quality of drinking water from microfiltered water dispensers

A comparison was made between the microbial quality of drinking water obtained from Microfiltered Water Dispensers (MWDs) and that of municipal tap water. A total of 233 water samples were analyzed. Escherichia coli (EC), enterococci (ENT), total coliforms (TC), Staphylococcus aureus, Pseudomonas aeruginosa and heterotrophic plate count (HPC) at 22 °C and 37 °C were enumerated. In addition, information was collected about the principal structural and functional characteristics of each MWD in order to study the various factors that might influence the microbial quality of the water. EC and ENT were not detected in any of the samples. TC were never detected in the tap water but were found in 5 samples taken from 5 different MWDs. S. aureus was found in a single sample of microfiltered water. P. aeruginosa was found more frequently and at higher concentrations in the samples collected from MWDs. The mean HPCs at 22 °C and 37 °C were significantly higher in microfiltered water samples compared to those of the tap water. In conclusion, the use of MWDs may increase the number of bacteria originally present in tap water. It is therefore important to monitor the quality of the dispensed water over time, especially if it is destined for vulnerable users.

Synergism between hydrogen peroxide and seventeen acids against six bacterial strains

AIMS

The objective of this study was to evaluate the bactericidal efficacy of hydrogen peroxide administered in combination with 17 mineral and organic acids authorized for use in the food industry.

METHODS AND RESULTS

The assays were performed on a 96-well microplate using a microdilution technique based on the checkerboard titration method. The six selected strains were reference strains and strains representative of contaminating bacteria in the food industry. Each synergistic hydrogen peroxide/acid combination found after 5-min contact time at 20°C in distilled water was then tested in conditions simulating four different use conditions. Thirty-two combinations were synergistic in distilled water; twenty-five of these remained synergistic with one or more of the four mineral and organic interfering substances selected. Hydrogen peroxide/formic acid combination was synergistic for all six bacterial strains in distilled water and remained synergistic with interfering substances. Six other combinations maintained their synergistic effect in the presence of an organic load but only for one or two bacterial strains.

CONCLUSIONS

Synergistic combinations of disinfectants were revealed, among them the promising hydrogen peroxide/formic acid combination.

SIGNIFICANCE AND IMPACT OF THE STUDY

A rapid screening method was proposed and used to reveal the synergistic potential of disinfectant and/or sanitizer combinations.

Management of dental unit waterline biofilms in the 21st century

Dental chair units (DCUs) use water to cool and irrigate DCU-supplied instruments and tooth surfaces, and provide rinsewater during dental treatment. A complex network of interconnected plastic dental unit waterlines (DUWLs) supply water to these instruments. DUWLs are universally prone to microbial biofilm contamination seeded predominantly from microorganisms in supply water. Consequently, DUWL output water invariably becomes contaminated by high densities of microorganisms, principally Gram-negative environmental bacteria including Pseudomonas aeruginosa and Legionella species, but sometimes contain human-derived pathogens such as Staphylococcus aureus. Patients and staff are exposed to microorganisms from DUWL output water and to contaminated aerosols generated by DCU instruments. A wide variety of approaches, many unsuccessful, have been proposed to control DUWL biofilm. More recently, advances in biofilm science, chemical DUWL biofilm treatment agents, DCU design, supply water treatment and development of automated DUWL biofilm control systems have provided effective long-term solutions to DUWL biofilm control.

Biofilms isolated from washing machines from three continents and their tolerance to a standard detergent

The goal of this comparative study was to investigate biofilm forming microorganisms living in washing machines (WMs). Biofilms were sampled from 11 washing machines from four countries and three continents. Among the 94 isolated strains, 30% were potential human pathogens. Representative strains were selected and biofilm formation was evaluated with the crystal violet (CV) assay. The majority of the WM isolates formed more biofilm than their reference strains. Biofilms of P. putida WM (the largest biofilm producer) were exposed to different concentrations (0.0007-7 g l(-1)) of the standard detergent IEC-A* at 30°C for 30 min and observed with confocal laser scanning microscopy. Using quantitative CVA, P. putida WM biofilm removal required higher detergent concentrations than the type strain. However, for both strains the recommended detergent concentration (7 g l(-1)) was insufficient to completely clean surfaces from cell debris and exopolymeric substances.

Microbial biofilm control within the dental clinic: reducing multiple risks

This short review focuses on biofilms in the dental clinic environment. Microbial biofilms are potentially a significant source of cross-contamination and cross-infection in the dental clinic. Biofilms in dental chair unit waterlines (DUWLs), suction hoses and fittings pose the most significant risk as these may come into contact with the patient during treatment. These can be managed effectively by regular disinfection using chemical disinfectants and procedures that have proven efficacy. As dental chair units (DCUs) are classified as medical devices, there is a requirement for DCU manufacturers to provide detailed guidance for their decontamination. Planned routine preventive maintenance of the dental clinic water network and good quality water will considerably minimise infection risks from microorganisms in tap water and has benefits for the operation of other clinic equipment. Regular and effective cleaning and disinfection of taps, sinks and splash-backs will help to minimise reservoirs and disseminators of potentially pathogenic bacteria from these areas.

Comparison of the microbial load of incoming and distal outlet waters from dental unit water systems in Istanbul

This is a cross-sectional study of the incoming and distal outlet water quality from 41 dental units in Istanbul, carried out to compare the total microbial loads using traditional culture method versus epifluorescence microscopy. The possible presence of Legionella pneumophila using traditional culture method was also analyzed. One hundred and twenty three samples were taken from the high-speed handpiece lines, air-water syringe lines and source (incoming) water supplies from 41 dental units. The samples were assayed for live/dead bacteria, heterotrophic bacterial counts and presence of L. pneumophila bacteria. Thirty nine out of 41 dental units (91%) were not able to meet the standard limit of 200 CFU/ml in dental unit waters. The live bacterial counts were 1-1.5 orders of magnitude higher than aerobic mesophilic heterotrophic bacteria. L. pneumophila (serogroup 2-14) was isolated from five out of 41 units. Some dental units were using commercially bottled (19 l) drinking water as a source. The source water of eight dental unit was heavily contaminated which were fed up by commercially bottled drinking water.