|Year : 2017 | Volume
| Issue : 1 | Page : 97-101
Assessment of Microbial Contamination in Dental-Unit Water Lines: An Analytical Study
Neethu Salam, Vinod M Mulamoottil, Benley George
Department of Public Health Dentistry, Pushpagiri College of Dental Sciences, Tiruvalla, Kerala, India
|Date of Web Publication||14-Mar-2017|
Department of Public Health Dentistry, Pushpagiri College of Dental Sciences, Tiruvalla, Kerala
Source of Support: None, Conflict of Interest: None
Introduction: Dental-unit water line (DUWL) contains various microorganisms. American Dental Association and the Centers for Disease Control and Prevention have suggested a standard for dental-unit water system water as water not having more than 200 cfu/ml. Aim: To assess the microbial contamination in DUWLs. Materials and Methods: Two dental chairs, each from four clinical departments, were randomly selected in this study. A total of 31 water samples were collected from each chair containing airotor line, scaler unit, 2-way syringe and oral rinse unit. In one dental chair in the Department of Periodontics, the sample from airotor point was not assessed, as it was not functional at the time of assessment. The samples were inoculated into blood agar, MacConkey agar and peptone water and cultured at 37°C overnight. Result: Colony-forming units were above 500 cfu/ml. The organisms identified were mostly gram-negative bacilli particularly Escherichia coli, Pseudomonas and Klebsiella, as well as gram-positive bacteria such as Enterococci. Conclusion: DUWLs are heavily contaminated with waterborne organisms from biofilm within the tubes as well as human pathogens as a result of the back-siphonage from oral cavity of patients. These organisms may cause serious systemic infections to patients, especially the children, the elderly and the immunocompromised. Periodic checking of anti-retraction valves and disinfecting within the dental water unit system are mandatory.
Keywords: Bacteria, biofilms, culture media, dental equipment
|How to cite this article:|
Salam N, Mulamoottil VM, George B. Assessment of Microbial Contamination in Dental-Unit Water Lines: An Analytical Study. J Indian Assoc Public Health Dent 2017;15:97-101
|How to cite this URL:|
Salam N, Mulamoottil VM, George B. Assessment of Microbial Contamination in Dental-Unit Water Lines: An Analytical Study. J Indian Assoc Public Health Dent [serial online] 2017 [cited 2020 Nov 24];15:97-101. Available from: https://www.jiaphd.org/text.asp?2017/15/1/97/201925
| Introduction|| |
The water obtained from dental units via 3-in-1 syringes, air rotors, and low-speed handpieces may be heavily contaminated with microorganisms and thus may be a potential source of infection for both practice staff and patients. The range of microorganisms includes both environmental organisms (e.g. Moraxella More Details sp. and Flavobacterium sp.) and opportunistic and true human pathogens (e.g. Pseudomonas aeruginosa, Legionella pneumophila, Mycobacterium sp., Candida sp., Actinomyces sp., Streptococcus sp. and Staphylococcus sp.). Such organisms may originate from incoming local water supplies, although organisms commonly found in the oral cavity have also been recovered, suggesting that some bacteria may be derived from the patient following back-siphonage.
The most common cause of dental-unit water contamination is believed to be the formation and subsequent sloughing off of microbial biofilms from the surfaces of tubing within dental-unit water systems. Dental equipment such as retracting shut-off valves, anti-retracting valves that tend to fail or water lines that are inaccessible contribute to a situation in which virtually every standard dental unit contains contaminated water. Although exposure to Pseudomonas, Moraxella, Staphylococcus and Legionella has been linked to dental water, the medical risk of dental-unit water line (DUWL) contamination is most significant to immune-deficient individuals.
Not only are these organisms intrinsically resistant to high temperatures and biocides, but also the biofilms they inhabit enhance their resistance. This should be of concern to infection control practitioners. Although some aspects of biofilm resistance are yet only poorly understood, the dominant mechanisms are thought to be related to the following aspects: (i) modified nutrient environments and suppression of growth rate within the biofilm; (ii) direct interactions among the exopolymer matrices, their constituents and antimicrobials, affecting diffusion and availability; and (iii) the development of biofilm/attachment-specific phenotypes. The bacterial colonisation of DUWLs can be used as a model to investigate the problem of waterborne biofilms in health care settings.
In 1993, Centers for Disease Control and Prevention recommended that dental water lines be flushed at the beginning of the clinic day to reduce the microbial load. However, studies have demonstrated this practice does not affect biofilm in the water lines or reliably improve the quality of water used during dental treatment.
Dental-unit water that remains untreated or unfiltered is unlikely to meet drinking water standards (<500 cfu/ml); therefore, one or more commercial devices and procedures designed to improve the quality of water should be employed. Hence, the aims of the study were to identify the number of colony-forming units present in dental-unit water samples and the presence of any human pathogens in the water samples.
| Materials and Methods|| |
The study was conducted in a dental college in central Kerala, India from March to May 2015. The samples were collected in two phases. In the first phase, 12 samples were collected and assessment done. In the second phase, 19 samples were collected and assessed in May 2015. In one dental chair in the Department of Periodontics, the sample from airotor point was not assessed, as it was not functional at the time of assessment. The study was done in two phases for the ease in carrying out the microbial analysis.
As per laboratory guidelines, about 100 ml (each) of water was collected from airotor lines, scaler units, 2-way syringes and oral rinse units of the selected eight dental chairs in the Departments of Pedodontics, Periodontics, Conservative Dentistry and Prosthodontics in the mid-morning hours and stored in labelled sterile bottles containing 0.1 g of sodium thiosulphate, which neutralise the effect of residual chlorine. The bottles were collected in a cool box and transferred to the Department of Microbiology, Pushpagiri Medical College Hospital, Tiruvalla.
Within an hour following collection, half portion from each sample was centrifuged at 4000 rpm for 5 min and was serially diluted 10-fold. Both centrifuged and non-centrifuged samples were inoculated into various media using sterile inoculating loops and incubated at 37°C overnight (18 h). The colonies were identified and counted. Gram staining and sub-culturing of required samples were done. Biochemical tests [indole test and triple sugar iron agar (TSI) test] were done on required samples to differentiate between Escherichia More Details coli and Klebsiella. In the indole test, a small amount of cultured sample was inoculated with peptone broth and incubated at 37°C for 24 h. Five drops of Kovacs reagent was directly added to the tube, and the tubes were shaken gently. For triple sugar iron agar test, the slants were inoculated with a pure culture by streaking over the entire surface of the slant and then stabbing into the butt and incubated at 37°C for 24 h.
| Results|| |
Sample N1 showed growth of gram-negative bacilli (GNB) in blood agar and lactose-fermenting colony in MacConkey agar. Gram staining revealed the presence of GNB. Indole test was positive and TSI test negative, which suggested the presence of E. coli. Sub-culture in blood agar showed bacilli, and MacConkey agar showed E. coli. Samples N2, N3 and N9 showed growth in blood agar. Sub-culture in blood agar and MacConkey agar showed the presence of bacilli. Samples N4 and N5 showed growth in blood agar. Sub-culture in blood agar showed bacilli, and MacConkey agar showed E. coli. Samples N6 and N7 showed growth in blood agar. Sub-culture in blood agar showed bacilli, and MacConkey agar showed Klebsiella. Sample N8 showed growth of GNB in blood agar and lactose-fermenting colony in MacConkey agar. Gram staining revealed the presence of gram-positive cocci (Enterococci) as well as GNB. Indole test was negative and TSI test positive, which suggested the presence of Klebsiella. Sub-culture in blood agar showed bacilli, and MacConkey agar showed bacilli and Enterococci.
Sample N1R showed growth of GNB in blood agar and lactose-fermenting colony in MacConkey agar. Indole test was positive and TSI test negative, which suggested the presence of E. coli.
Samples N2R, N3R, N4R, N5R, N6R, N7R, N8R and N9R showed growth of GNB in blood agar, MacConkey agar and peptone water. Samples NC1 and NC2 showed growth in blood agar and peptone water. Sub-culture on MacConkey agar showed Klebsiella.
Sample NC3 showed growth in peptone water. Sub-culture on MacConkey agar showed E. coli. Sample NC4 showed growth in blood agar and peptone water. Sub-culture on MacConkey agar showed E. coli.
Sample NP1 showed growth in MacConkey agar and peptone water. Sub-culture on MacConkey agar showed Pseudomonas. Samples NP2 and NP3 showed growth in blood agar and peptone water. Sub-culture on MacConkey agar showed Pseudomonas. Sample NP4 showed growth in peptone water. Sub-culture on MacConkey agar showed E. coli.
Sample NPR1 showed growth in blood agar, MacConkey agar and peptone water. Sub-culture on MacConkey agar showed Klebsiella. Sample NPR2 showed growth in blood agar and peptone water. Sub-culture on MacConkey agar showed E. coli. Sample NPR3 showed growth in blood agar and peptone water. Sub-culture on MacConkey agar showed Klebsiella.
Sample NPT1 showed growth in blood agar and peptone water. Sub-culture on MacConkey agar showed E. coli. Although sample NPT2 showed growth in peptone water, sub-culture on MacConkey agar showed E. coli [Table 1] and [Table 2].
|Table 1: Colonisation of microorganisms on dental-unit water lines in dental chairs in the Departments of Pedodontics and Periodontics|
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|Table 2: Colonisation of microorganisms on dental-unit water lines in dental chairs in Prosthodontics and Conservative Dentistry|
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| Discussion|| |
The results of this study indicated that DUWLs are heavily contaminated with waterborne as well as human pathogenic organisms. Most units had colony-forming units above 500 cfu/ml, which is not acceptable as per American Dental Association (ADA) recommendations. The high level of contamination of DUWLs demonstrated in this study confirmed the results of others.,,, In this study, Pseudomonas were detected in the water samples from handpiece and 3-way syringe, which was also similar to a study conducted in Mangalore.
Some previous studies in India, showed that flushed samples from the same source had reduced microbial load to some extent when compared to the unflushed samples; however, still the values were high. In addition, it might not affect the wide variety of organisms. Therefore, flushing does not play any significant role in disinfection processes. Previous studies across the globe on percentage reduction of viable counts and biofilm coverage after exposure to disinfectants and flushing showed only 9.1% reduction in viable count with flushing and only 0.5% reduction in biofilm with flushing. However, exposure to disinfectants such as chlorhexidine, Betadine, sodium hypochlorite, Alpron, Sterilox and Oxygenal showed 100% reduction in viable count; however, still the biofilm persisted. The chemical disinfectants should not cause harm to patients as well as the dental-unit system. There is increased need to conduct further studies to find out the corrosive and toxic nature of chemical disinfectants used as well as to find out effective disinfection process within the DUWL system, thereby creating a healthy dental unit to the patients. The limited sample size and the non-estimation of the bacterial count are the limitations of this study.
Hence, disinfection of the water source and DUWLs should be done regularly for proper infection control in dental clinics and hospitals. Future research should focus on developing chemical disinfectants using nanoparticles, which would limit the drawbacks of the currently available chemical disinfectants in the market.
| Conclusion|| |
The colony-forming units in water samples are higher in number than the ADA recommended value. Presence of indicator organisms such as E. coli and Enterococci indicates faecal contamination of water and growth of other pathogenic organisms. The source of contamination may be the source of water or back-siphonage of organisms from the oral fluids of patients. GNBs such as Pseudomonas may cause several systemic infections, mainly to the immunocompromised, the elderly and children.
I thank Dr. Jose Paul, MD and Dr. Seema Oommen, MD, Department of Microbiology, Pushpagiri Institute of Medical Sciences and Research Centre for their valuable support in the study. I extend my sincere thanks to our Principal, Dr. Aby Mathew T, Dr. Biju Sebastian, our Vice Principal (Academics) and Dr. Nebu Thomas George, Reader, Department of Periodontics for their support in conducting this study.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2]