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Applied and Environmental Microbiology, August 2000, p. 3363-3367, Vol. 66, No. 8
CAMR, Porton Down, Salisbury, SP4
0JG,1 Dental Practice, Town Street,
Shepton Mallet BA45 BE,2 Department of
Clinical Dental Sciences, University of Liverpool, Liverpool, L69
3BX,3 and Leeds Dental Institute,
Leeds, LS2 9LU,4 United Kingdom
Received 24 February 2000/Accepted 4 May 2000
Dental-unit water systems (DUWS) harbor bacterial biofilms, which
may serve as a haven for pathogens. The aim of this study was to
investigate the microbial load of water from DUWS in general dental
practices and the biofouling of DUWS tubing. Water and tube samples
were taken from 55 dental surgeries in southwestern England.
Contamination was determined by viable counts on environmentally selective, clinically selective, and pathogen-selective media, and
biofouling was determined by using microscopic and image analysis techniques. Microbial loading ranged from 500 to 105
CFU · ml
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Microbial Biofilm Formation and Contamination of
Dental-Unit Water Systems in General Dental Practice
1; in 95% of DUWS water samples, it
exceeded European Union drinking water guidelines and in 83% it
exceeded American Dental Association DUWS standards. Among visible
bacteria, 68% were viable by BacLight staining, but only
5% of this "viable by BacLight" fraction produced colonies on agar plates. Legionella pneumophila,
Mycobacterium spp., Candida spp., and
Pseudomonas spp. were detected in one, five, two, and nine
different surgeries, respectively. Presumptive oral streptococci and
Fusobacterium spp. were detected in four and one surgeries,
respectively, suggesting back siphonage and failure of antiretraction
devices. Hepatitis B virus was never detected. Decontamination
strategies (5 of 55 surgeries) significantly reduced biofilm coverage
but significantly increased microbial numbers in the water phase (in
both cases, P < 0.05). Microbial loads were not
significantly different in DUWS fed with soft, hard, deionized, or
distilled water or in different DUWS (main, tank, or bottle fed).
Microbiologically, no DUWS can be considered "cleaner" than others.
DUWS deliver water to patients with microbial levels exceeding those
considered safe for drinking water.
Applied and Environmental Microbiology, August 2000, p. 3363-3367, Vol. 66, No. 8
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
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