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

Abstract

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.

Keywords: 16S rRNA gene sequencing; biofilm; dental unit water line; microbial contamination; pathogenic species.

Figure 1

Scanning electron micrograph of the inner surface of DUWL tubing. A thick biofilm mass is seen on the inner surface of the tubing.

Figure 2

Total viable counts from water samples collected from dental unit hand pieces. Samples were collected before and after treatment, 10-fold serially diluted up to 10⁻⁵ and plated on different culture media. The plates were then incubated in different atmospheric conditions for different incubation times as described in “methods”. P < 0.05 Mann Whitney U.

Figure 3

Total viable counts from water samples collected from dental unit water storage bottles. Samples were collected before and after treatment, 10-fold serially diluted up to 10⁻⁵ and plated on different culture media. The plates were then incubated in different atmospheric conditions for different incubation times as described in “methods”. P < 0.05 Mann Whitney U.

Figure 4

Bacterial counts from the biofilm harvested from DUWL tubing before and after treatment. Biofilm was scraped off the tubing surface using sterile dental probe and suspended in sterile PBS. Serial 10-fold dilutions (up to 10⁻⁵) were prepared and plated on different culture media. P < 0.05 Mann Whitney U.