Evaluation of 3 dental unit waterline contamination testing methods

Abstract

Previous studies have found inconsistent results from testing methods used to measure heterotrophic plate count (HPC) bacteria in dental unit waterline (DUWL) samples. This study used 63 samples to compare the results obtained from an in-office chairside method and 2 currently used commercial laboratory HPC methods (Standard Methods 9215C and 9215E). The results suggest that the Standard Method 9215E is not suitable for application to DUWL quality monitoring, due to the detection of limited numbers of heterotrophic organisms at the required 35°C incubation temperature. The results also confirm that while the in-office chairside method is useful for DUWL quality monitoring, the Standard Method 9215C provided the most accurate results.

Chart

R2A with SimPlate for HPC method scatterplot, displaying legend markers indicating the range of the corresponding HPC Sampler value for each sample. Note that 2 handpiece samples for which no CFUs were detected by HPC Sampler were excluded. All samples with R2A >1500 CFU/ml had HPC Sampler values >500 CFU/ml, while only 1 sample with R2A <1500 CFU/ml had an HPC Sampler value >500 CFU/ml.