Pseudomonas aeruginosa and Achromobacter sp. Clonal Selection Leads to Successive Waves of Contamination of Water in Dental Care Units

Abstract

Dental care unit waterlines (DCUWs) consist of complex networks of thin tubes that facilitate the formation of microbial biofilms. Due to the predilection toward a wet environment, strong adhesion, biofilm formation, and resistance to biocides, Pseudomonas aeruginosa, a major human opportunistic pathogen, is adapted to DCUW colonization. Other nonfermentative Gramnegative bacilli, such as members of the genus Achromobacter, are emerging pathogens found in water networks. We reported the 6.5-year dynamics of bacterial contamination of waterlines in a dental health care center with 61 dental care units (DCUs) connected to the same water supply system. The conditions allowed the selection and the emergence of clones of Achromobacter sp. and P. aeruginosa characterized by multilocus sequence typing, multiplex repetitive elements-based PCR, and restriction fragment length polymorphism in pulsed-field gel electrophoresis, biofilm formation, and antimicrobial susceptibility. One clone of P. aeruginosa and 2 clones of Achromobacter sp. colonized successively all of the DCUWs: the last colonization by P. aeruginosa ST309 led to the closing of the dental care center. Successive dominance of species and clones was linked to biocide treatments. Achromobacter strains were weak biofilm producers compared to P. aeruginosa ST309, but the coculture of P. aeruginosa and Achromobacter enhanced P. aeruginosa ST309 biofilm formation. Intraclonal genomic microevolution was observed in the isolates of P. aeruginosa ST309 collected chronologically and in Achromobacter sp. clone A. The contamination control was achieved by a complete reorganization of the dental health care center by removing the connecting tubes between DCUs. D ental instruments on dental care units (DCUs), such as ultrasonic scalers, air scalers, and high-speed turbine dental handpieces, are cooled by DCU-supplied water, which also irrigates and cools the tooth surface during dental treatment (1). Water is also supplied to the DCU cup filler outlet used by patients for oral rinsing and to the bowl rinse outlet rinsing the DCU spittoon. Therefore, DCU waterlines (DCUWs) consist of a complex network formed by meters of narrow-bore plastic tubing of mostly 2-to 3-mm internal diameter. In narrow-bore tubes, a thin immobile layer of fluid, called the hydrodynamic boundary layer, exists at the interface of the lumen wall and the moving water (2). This hydrodynamic phenomenon is associated with water stagnation when the DCU is not used, and heating of water to at least 20°C enhances the development of microbial biofilm in the tubes (3).The DCUWs appear to be a technological niche in which complex interactions occur among members of the microbial community (4-6). Regarding bacteria, DCUWs have been shown to promote the formation of biofilm, predominantly seeded from environmental bacteria in the water supply (4-6). More rarely, human bacteria such as staphylococci or oral bacteria have been detected, indicating a retraction of oral fluids from the surgical devices to the wate...

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