Biofilms augment the number of free-living amoebae in dental unit waterlines

Freshwater amoebae are ubiquitous. Some species can cause infections in hum ans while others can ingest and protect opportunistic bacteria. Although th e presence of free-living amoebae in various water sources has been reporte d, few studies have looked at their concentration, which may be clinically relevant, especially if they are present in healthcare devices. A simple te chnique was used to detect, observe, and evaluate the concentration of free -living amoebae in dental unit and tap water samples. Fifty-three water sam ples were collected from 35 dental units (air/water syringes) and 18 water taps. The technique was based on the ability of waterborne bacteria to crea te a biofilm and serve as substratum for the development of amoebae natural ly present in the water samples. Laboratory-grown freshwater biofilms suppo rt the proliferation of a wide variety of free-living amoebae. All the dent al unit water samples tested contained amoebae at concentrations up to 330/ mL, or more than 300 times the concentration in tap water from the same sou rce. Hartmanella, Vanella, and Vahlkampfia spp. were the most frequently en countered. Naegleria and Acanthamoeba spp. were also present in 40% of the samples. Four of the samples collected from dental units, but none from wat er taps, contained amoebae able to proliferate at 44 degreesC. Biofilms tha t form inside some dental instruments can considerably increase the concent ration of free-living amoebae, some of which are potential human pathogens. (C) 2001 Editions scientifiques et medicales Elsevier SAS.