Presence of microorganisms in used ultrasonic cleaning solutions

This study analyzed ultrasonic cleaning solutions for bacterial contamination and for antibacterial activity after the solutions were used for a full day in dental offices. Ten dental offices ultrasonically cleaned their instruments by their standard procedures for a full day using one batch of their normal cleaning solution. The solutions were then quantitatively analyzed for levels of bacterial contamination and for antibacterial activity against Staphylococcus aureus and Pseudomonas aeruginosa. Levels of bacterial contamination ranged from 0 to 10,000 CFU/ml in the used solutions, and the four used cleaning solutions involved exhibited varying levels of activity against the two test bacteria. The four fresh unused cleaning solutions involved were also analyzed for minimal inhibitory concentration (MIC), minimal bacteriocidal concentration (MBC), and killing times against S. aureus, P. aeruginosa and Salmonella choleraesuis. None of the four cleaning solutions involved made any antimicrobial label claims, because they were marketed as cleaners, not antimicrobial agents. Three of the four agents exhibited some antibacterial activity against all three test bacteria but required greater than 10 minutes to kill all three. One solution exhibited high activity and kill times of less than 1 minute against all three test bacteria. Repeat testing of this solution in 17 dental offices confirmed its antimicrobial activity during use. Bacterial contamination may be present in used ultrasonic cleaning solutions. Use of an antimicrobial cleaning solution is one approach to manage this potential for contamination.