EFFECT OF ULTRASONIC CLEANING ON MICROORGANISMS

Purpose: To establish a method to measure microbial kill caused by ult rasonic cleaning. Secondarily, to estimate the escape of bacteria from the ultrasonic cleaning solutions during operation of the unit. Mater ials and Methods: Three commercial enzymatic detergents and saline wer e used as cleaners. Depending on detergent, initial operational temper ature was 21 degrees C, 37 degrees C or 60 degrees C. Streptococcus mu tans ATCC 25175 (S. mutans suspensions) was adjusted to a final concen tration of 1.0 x 10(8) cells/mL, in saline. Suspensions (2000 mt) at t he desired temperatures were added to the cleaner. Aliquots were remov ed, serially diluted in letheen broth and spread plated over mitis sal ivarius agar. Appropriate amounts of detergent solutions were added to S. mutans suspensions and the cleaner operated for 20 minutes. Aliquo ts were then removed and plated. The process was repeated twice. Plate s were aerobically incubated at 37 degrees C for 7 days and the coloni es counted. The procedure was repeated using three temperatures of S. mutans suspensions (21 degrees C, 37 degrees C or 60 degrees C), but w ithout detergent or ultrasound. Also, detergents were added to 21 degr ees C S. mutans suspensions and allowed to sit for 20 minutes without ultrasonic cleaning. Microbial sampling was done as previously describ ed. Results: Results when ultrasound was used indicated that little ki ll (5-15%) occurred in 21 degrees C or 37 degrees C detergent solution s. Greater kill (25-35%) was noted with 21 degrees C and 37 degrees C saline. Complete kill was accomplished with 60 degrees C saline or the 60 degrees C detergent solution. When ultrasound and detergent were n ot used, there was no kill in 21 degrees C and 37 degrees C saline, bu t complete kill in 60 degrees C saline. In the absence of ultrasound n o kill was noted in 21 degrees C S. mutans suspensions to which deterg ent had been added. Total kill of S. mutans was observed in 60 degrees C saline or 60''C detergent with ultrasound or after a 20-minute expo sure in 60 degrees C saline without ultrasonic cleaning. Very few bact eria escaped from the ultrasonic cleaning solutions into the air durin g the cleaning process. Placement of the unit lid effectively reduced emissions to zero.