A comparison of two ultrasonic methods for detaching biofilms from naturalsubstrata

Two types of ultrasound applications are commonly used in order to remove b acteria from sediment for subsequent direct enumeration: ultrasonic baths a nd narrow tip ultrasonic generators. By measuring four parameters (total nu mber of bacteria, number of ETS-active bacteria, amount of proteins and wei ght of fine sediment obtained in sonicated juices), we compared the biofilm removal of the optimal ultrasound exposure time previously obtained using the ultrasonic bath with the removal by a method using a narrow tip ultraso nic generator. To obtain comparable removal efficiencies estimated by prote in contents in sonicated juices, the ultrasonic bath method required an ult rasound exposure time more than 10 times that with a narrow tip ultrasonic generator. Furthermore, the two methods provided significantly different ba cterial counts because of an alteration of the sediment with the ultrasonic bath. Thus, a narrow tip ultrasonic generator is more suitable than an ult rasonic bath for the analysis of biofilms developed on sand.