Isolation of an unusual fungus in treated dental unit waterlines.
BACKGROUND
Numerous organisms have been identified in dental unit waterlines, or DUWLs. Decontamination of DUWLs focuses on maintaining heterotrophic, mesophilic bacteria below 200 colony-forming units per milliliter as recommended by the ADA.


METHODS
The authors conducted a study to test the efficacy of a continuous-use, stabilized chlorine dioxide proprietary compound to decrease the number of bacteria in DUWLs. The authors used three dental units with self-contained water systems to test the product and three similar units as controls. They aseptically collected water samples weekly according to recommended methods, plated the samples on R2A agar and incubated them for seven days.


RESULTS
The authors isolated heterotrophic, mesophilic bacteria from treatment and control units for eight weeks. In the ninth week, the predominant isolates from one of the treatment units changed in appearance to small, dark, shiny colonies that the authors tentatively identified as fungal. The authors then isolated similar colonies from the source tap water and ultrasonic and handpiece lines. They added three additional dental units from the same clinic in the sixth week of the study and isolated similar fungal colonies from them after five weeks of treatment. The authors performed DNA sequencing with an automated sequencer and identified the organism Exophiala mesophila.


CONCLUSIONS
The authors did not observe fungal isolates in the control units, which suggests that continuous waterline treatment may cause proliferation of a fungus present in small amounts in source water. CLINICAL IMPLICATIONS. The findings of this study indicate the need to monitor water quality regularly when treating waterlines with continuous-use chemical cleaners.
Porteous
Nuala B
NB
The University of Texas Health Science Center at San Antonio, 78229, USA. porteous@uthscsa.edu
Redding
Spencer W
SW
Thompson
Elizabeth H
EH
Grooters
Amy M
AM
De Hoog
Sybren
S
Sutton
Deanna A
DA
D001419:Bacteria / Q000302:isolation & purification; D017606:Chlorine Compounds / Q000627:therapeutic use; D015169:Colony Count, Microbial; D019551:Dental Disinfectants / Q000627:therapeutic use; D003748:Dental Equipment / Q000382:microbiology*; D004866:Equipment Contamination / Q000517:prevention & control; D005093:Exophiala / Q000302:isolation & purification*; D006801:Humans; D019552:Infection Control, Dental; D010087:Oxides / Q000627:therapeutic use; D013997:Time Factors; D014871:Water Microbiology
D017606:Chlorine Compounds; D019551:Dental Disinfectants; D010087:Oxides; C025109:chlorine dioxide