Читать книгу Oral Biofilms - Группа авторов - Страница 34

A number of solutions have been introduced on the market, but it is beyond the purpose of this paper to review the various products that are available. Principally, the methods are of two approaches, those that disinfect/reduce bacteria from the output water, and those that attack and eliminate/prevent the biofilm in the DUWLs [4, 22]. The first is attractive since it is based on a continuous delivery of the disinfectant, needs less manipulation and care, but has the disadvantage that it may expose patients to antimicrobials that are still present in the water when it is used. A continuous delivery, such as using hydrogen peroxide, may also efficiently prevent biofilm formation in the DUWLs once they have been eliminated [23]. Another disadvantage is that disinfection is only performed at use – and bacterial growth and biofilm formation may take place in units that are only sporadically used or over the weekend and during vacations. The principle of non-continuous delivery is based on the disinfection being active for longer periods of time, such as overnight or at weekends, which allows for a more efficient elimination of the biofilm using chlorine products. An established biofilm is much more difficult to eradicate. It is sometimes necessary to expose the entire DUWL system to a strong disinfectant (shock treatment) in order to remove the biofilm. Sodium hydroxide 0.1 M (0.8%) or sodium hypochlorite 0.5% has been suggested [3, 24, 25]. However, it should only be used when necessary due to the risk of damage to metal pieces (e.g., valves and connections) within the DUWL by corrosion if used frequently and for longer periods of time. Importantly, these strong solutions should be stained (e.g., methylene blue) to make it possible to check that the chemicals have been washed off. In severe cases, when there is a total blockage in the water lines, the radical solution is to exchange the lines with new ones, although this is expensive [3].

The threshold for a sufficient water-cleaning system within the EU has been recommended to be <200 CFU/mL and the water in a DUWL should be checked yearly. The American Dental Association (ADA) has recommended the same, while the recommendation of the Center for Disease Control (CDC) for drinking water is 500 CFU/mL [4]. The Swedish recommendations, which were set in 2006 [26] and before the EU recommendation was decided, used the threshold of 100 CFU/mL and is still in use [27, 28]. In practice it means that we accept, although with attention, up to 500 CFU/mL for heterofermentative fast-growing (<2 days) bacteria at room temperature (22 °C). In order to get a better picture of the “internal life” and presence of a biofilm, in our lab we practice incubation for 7 days for slow-growing bacteria, which should not exceed 5,000 CFU/mL according to the drinking water standard for tap water in Sweden [3]. Such high levels indicate the presence of biofilms in a DUWL and should be shock treated. However, when regular antimicrobial treatment of each DUWL in a clinic is performed, such high numbers of bacteria are rare.