Microflora of dental unit waterlines

Authors

Shirleen Castro, University of the Pacific
Grace Chung, University of the Pacific
Heather Leo, University of the Pacific
Chris Nguyen, University of the Pacific
Natalie Okuhara, University of the Pacific

Lead Author Affiliation

Dental Surgery Program

Introduction/Context/Diagnosis

Facilities treat water to control and prevent Legionella pneumophila proliferation, but there are still reported cases of Legionnaire's disease. L. pneumophila can proliferate in amoebae that thrive in water systems. Understanding this relationship may help to reduce Legionella in DUWLs and prevent future infections as some studies have found three hundred times more amoebae in DUWL than tap water. Our study evaluated the presence of amoebae and other microorganisms in DUWLs. We hypothesized that there will be a higher concentration of amoeba and microbes in tap water and in DUWLs prior to a two minute flushing.

Methods/Treatment Plan

We employed a concentrating method of centrifuging samples and decanting the top layer. We plated & incubated the remaining concentrated volume onto buffered charcoal yeast extract BCYE (for amoeba & legionella growth) and Sabdex plates (for fungal growth).

Results/Outcome

No amoebae were detected. Bacterial and fungal colonies were detected in both DUWLs and tap water. Pink colonies were detected on all DUWL samples, but none in tap water. Two types of pink colonies were identified through Gram staining. White colonies were detected in both DUWL and tap water. White colonies from DUWL and tap water had different biological properties.

Significance/Conclusions

Our results suggests presumptively the presence of fungi, Legionella bozemanii, Brevibacteria, Pseudomonas sp. and Methylbacterium sp.. We suspect the pink colonies are Methylbacterium. The Gram stains indicated poorly-stained, light pink rods. Methylbacterium are aerobic and fastidious microbes that can survive traditional disinfection techniques. The white colonies on DUWL BCYE plates were slowgrowing colonies, easily de-stained, possibly Gram negative, rod-shaped, and fluoresced under UV light, which are properties Hardy Diagnostics details for Legionella bozemanii. There were two distinctly contrasting white colonies on DUWL and tap samples, suggesting DUWL may allow other microbes to thrive in the absence of common contaminants in tap water. Future studies would use larger sample sizes, samples from other clinics, and run additional biochemical tests. Lastly, two of the microbes identified presumptively are opportunistic, and their presence indicates a need to treat water sources or use sterile saline water to prevent infections in susceptible patients.

Comments/Acknowledgements

This project was supported by Microbiology MC224 at the University of the Pacific, Arthur A. Dugoni School of Dentistry.

Location

University of the Pacific, Dugoni Dental School, San Francisco, CA

Format

Poster

Poster Session

Faculty, Student, and Staff Presentations