Oral Bacteria Counter Using Dielectrophoretic Impedance Measurement: Usefulness and Usage Considerations

Background: The oral cavity hosts numerous bacteria that are associated with various systemic diseases. The Oral Bacteria Counter (PHC Corporation, Tokyo, Japan), a microorganism quantitative analyzer that utilizes dielectrophoretic impedance measurements, enables rapid bacterial counting and is widely used in dental practice in Japan. However, it may also detect nonviable bacteria. This study aimed to assess the impact of disinfectants, electrolytes, and viscosity on the accuracy of the Oral Bacteria Counter and to determine whether it measures non-viable bacteria similarly to viable bacteria.

Methods: To evaluate the effect of the disinfectants, samples of 7% povidone-iodine (PV-I), 0.2% benzethonium chloride, 5% chlorhexidine (CHX), 0.2% CHX, 0.05% CHX, sterile water, and saline were measured using the Oral Bacteria Counter. The effect of viscosity was assessed by mixing sterile water with glycerol in various ratios and measuring the dielectrophoretic impedance of the bacterial counts at different viscosities. For the electrolyte effects, samples of Staphylococcus aureus diluted in sterile water or saline were measured using the Oral Bacteria Counter. Additionally, samples of 7% PV-I or 5% CHX diluted in sterile water or saline were measured. Bacterial counts were then measured and compared using the Oral Bacteria Counter, our developed delayed real-time polymerase chain reaction (DR-PCR) method (which quantifies only viable bacteria), and culture methods.

Results: Disinfectants such as 5% CHX and 7% PV-I produced high readings on the Oral Bacteria Counter, even when no viable bacteria were present. Higher glycerol concentrations, which increased the viscosity, resulted in lower bacterial counts. The presence of electrolytes, particularly saline, led to higher readings on the Oral Bacteria Counter, which detected both viable and non-viable bacteria, whereas DR-PCR and culture methods did not detect non-viable bacteria.

Conclusion: The Oral Bacteria Counter may be influenced by disinfectants, viscosity, and electrolytes, leading to potential inaccuracies in bacterial quantification. For accurate bacterial measurements, it is essential to consider these factors and ideally combine the results from the Oral Bacteria Counter with methods such as DR-PCR for more reliable assessment.