S28: Antimicrobial Effects of Coupled Hydrodynamic and Ultrasound-induced Stress

            The traditional paradigm of microbial control in industry involves the application of microbicidal chemicals.  However, non-chemical microbial control technologies can be an effective option in situations where it is desirable to limit the use of chemical biocides, such as in cooling water systems and industrial process waters.   A commercially available non-chemical device (Sonoxide®) was configured to a model laboratory system and experiments conducted using Pseudomonas putida.  Results revealed that growth and respiration were rapidly inhibited without a concurrent loss of viability from the treated population.  These results were also replicated using a native microbial population in a cooling tower system.  Damage to cell membranes was evident via fluorescent microscopy and the use of engineered reporter strains containing lux genes fused with various stress response promoters.  The fabA reporter strain (reporting membrane damage) was immediately responsive, with slower responses from recA and groEL reporter strains (DNA and protein damage, respectively).  An additional consequence of treatment was a reduced ability of treated populations to form biofilms, which may be a reflection of inhibited growth.   In summary, the non-chemical treatment caused a biostatic effect on treated cells induced via sub-lethal damage to several cellular systems, including cell membranes.  The study demonstrates that biostasis can be an effective mechanism for microbial control in some industrial systems, and provides insight into understanding and applying non-chemical microbial control technology to solve real world problems of microbial contamination.