A Comparison of Two Ultrasonic Methods for Detaching Biofilms from Natural Substrata

Two types of ultrasound applications are commonly used in order to remove bacteria from sediment for subsequent direct enumeration: ultrasonic baths and narrow tip ultrasonic generators. By measuring four parameters (total number of bacteria, number of ETS‐active bacteria, amount of proteins and weight 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 ultrasonic generator. To obtain comparable removal efficiencies estimated by protein contents in sonicated juices, the ultrasonic bath method required an ultrasound exposure time more than 10 times that with a narrow tip ultrasonic generator. Furthermore, the two methods provided significantly different bacterial counts because of an alteration of the sediment with the ultrasonic bath. Thus, a narrow tip ultrasonic generator is more suitable than an ultrasonic bath for the analysis of biofilms developed on sand.