Methods: One-hundred milliliter (100 mL) samples were taken from the handpiece lines, air/water syringe lines, and the source tap water in twenty-one randomly selected dental operatories in a teaching institution. Each sample was cultured on HPC Samplers (Millipore Corp., MA), R2A agar (Standard Method 9215C), and on SimPlateTM for HPC (IDEXX Labs, ME). Bacterial colonies were counted after recommended incubation periods and reported accordingly. Isolates were picked and purified for characterization using molecular identification.
Results: The SimPlateTM for HPC underestimated bacterial counts when compared with R2A agar and HPC Samplers. Correlations were weak between bacterial counts from SimPlateTM and the other two methods, while R2A agar and HPC Samplers had good correlation. Two different bacterial colony types were isolated from SimPlateTM for HPC, five from Millipore, and fourteen types from R2A. One species, Sphingomonas parapaucimobilis was isolated from all three substrates.
Conclusion: This study suggests that SimPlateTM for HPC, used in commercial laboratories, is not suitable for application to DUWL quality monitoring, due to the detection of limited numbers of heterotrophic organisms at required 35oC incubation temperature. The study also confirms that HPC Samplers are useful for in-office chairside DUWL quality monitoring and the spread plate R2A agar laboratory method provides the most accurate results.