use of ultrasonic imaging to evaluate the effect of protozoan grazing and movement on the topography of bacterial biofilms

This study evaluated the effect of protozoan movement and grazing on the topography of a dual-bacterial biofilm using both conventional light microscopy and a new ultrasonic technique. Coupons of dialysis membrane were incubated in Chalkley's medium for 3 days at 23°C in the presence of bacteria (Pseudomonas aeruginosa and Klebsiella aerogenes) alone, or in co-culture with the flagellate Bodo designis, the ciliate Tetrahymena pyriformis or the amoeba Acanthamoeba castellanii. Amoebic presence resulted in a confluent biofilm similar to the bacteria-only biofilm while the flagellate and ciliate created more diverse biofilm topographies comprising bacterial microcolonies and cavities. The four distinct biofilm topographies were successfully discerned with ultrasonic imaging and the method yielded information similar to that obtained with conventional light microscopy. Ultrasonic imaging provides a potential way forward in the development of a portable, nondestructive technique for profiling the topography of biofilms in situ, which might aid in the future management of biofouling.