Water quality and biofilm formation in dental unit waterline systems in Mangaung, Free State

Abstract

Microbial contamination of dental unit water exposes personnel and patients to a plethora of potential infectious organisms. The objective of this study was to analyse bacterial water quality and determine the presence of biofilm-associated organisms in dental chair waterlines in 21 oral healthcare facilities in Mangaung, South Africa. Ten dental chair units (DCUs) with an open-water system (i.e., water sourced from municipal water) were analysed, while eleven DCUs with a closed-water system (i.e., utilising a reservoir bottle attached to the DCU) were also analysed. A set of questions was administered to survey, amongst others, the age and cleaning methods of the DCUs utilised at each facility. Standard water sampling procedures were followed in accordance with the South African National Standard 241:1(2015) (SANS, 2015) for acceptable drinking water quality. Heterotrophic plate counts and total coliforms were determined. Heterotrophic plate counts have been widely adopted as a standard technique for microbiological testing and safety management of drinking water. The heterotrophic plate count is a microbiological parameter that can quantify the formation of biofilm in water systems. The permissible number of heterotrophic bacteria in drinking water according to the SANS 241:1 should be less than 1 000 colony forming units per millilitre of water (SANS,2015). Total coliform bacteria were analysed because they are used as indicators to measure the degree of pollution and sanitary quality of water. The presence of these bacteria in drinking water does not necessarily mean that the drinking water will cause disease. However, it is an indication that the water supply may be vulnerable to contamination. Their presence therefore indicates that disease-causing organisms may be present in drinking water. The permissible number of total coliform bacteria in drinking water according to the SANS 241:1 should be less than 10 colony forming units per 100 millilitres of water. Pseudomonas aeruginosa and Legionella spp. were detected at the end usage point of the dental water in the DCUs under study. Pseudomonas aeruginosa lives in the environment and can be spread to individuals in healthcare settings when they are exposed to water or soil that is contaminated with this bacteria. Resistant strains P. aeruginosa can also spread in healthcare settings from one person to another through contaminated hands, equipment, or surfaces. Pseudomonas aeruginosa causes infections in the blood, lungs (pneumonia), or other parts of the body post-surgery or when inhaled into the lungs. P. aeruginosa from biofilm that colonises DUWLs contaminate the water that is used in oral healthcare procedures. Legionella is a rod-shaped (bacillus) gram-negative bacteria that causes a form of pneumonia. It exists in natural water, such as lakes or rivers, but in small numbers do not cause a potential health risk. However, with favourable conditions and nutrients it can live and proliferate in domestic water systems. Legionnaires' disease is caused by the Legionella pneumophila bacteria. It is the most serious and potentially fatal of the legionellosis illnesses. Other less serious diseases caused by Legionella spp. are Pontiac fever and Lochgoilhead fever. Legionella can be transmitted to individuals if they inhale air droplets of contaminated water. In an oral healthcare facility this can be from the aerosols created from high-speed drills or an ultrasonic scaler. The presence of P. aeruginosa and Legionella spp. in dental chair unit water poses a serious risk for patients who are immunocompromised. Total bacterial counts significantly exceeded the SANS 241:1 (SANS, 2015) standard of <10 × 103 CFU ml-1 of water for both the open and closed systems (1.48-6.94 × 104 CFU ml-1). Total coliform counts revealed that coliforms were present in the water source (tap water) that was supplied to the DCUs and reservoir bottles. Even though the fact that the total coliform counts were below the SANS 241:1(SANS, 2015) recommendation of <10 CFU 100 ml-1, the presence of coliforms suggested the presence of faecal contamination that could have served as a precursor for biofilm formation. The level of total coliforms present in the distiller and reservoir bottles may have occurred as a result of improper bottle handling and inappropriate aseptic techniques. P. aeruginosa was not detected in the tap water of the closed system DCUs, but it was detected in fast handpieces, reservoir bottles, and distiller bottles. Legionella spp. (22 CFU ml-1) were present in the output water from one fast handpiece of an open system DCU. The internal surfaces of all the sampling sites were swabbed to determine the presence of biofilm-associated organisms. It was found that the internal surfaces of taps, fast handpieces, distiller bottles, and reservoir bottles all exhibited mean counts that exceeded the SANS 241:1 (SANS, 2015) standard for heterotrophic bacteria. Total coliforms, that exceeded the SANS 241:1 (SANS, 2015) standard for total coliform bacteria, were identified in the fast handpieces of both the open and closed system DCUs and in the distiller bottles of the closed systems. Total coliform counts in reservoir bottles were lower but were not detected on the inner surfaces of taps in either the open or closed systems. P. aeruginosa, at a mean count of 3.64 × 104 CFU ml-1, was detected on the inner tap surfaces of the open system DCUs. No P. aeruginosa was detected in the fast handpieces of either the open or the closed system DCUs, but it was present on the inner surfaces of reservoir bottles (5.9 × 101 CFU ml-1) and the fast handpieces (1.5 × 100) of closed system DCUs.