Simultaneous Bdellovibrio bacteriovorus–Bacteriophage Dosing with SODIS for Treatment of Environmental Water Sources

The predatory bacterium Bdellovibrio bacteriovorus HW1 and bacteriophage ABTW1 were applied simultaneously, with solar disinfection (SODIS), for the reduction of Acinetobacter baumannii in environmental water sources. The B. bacteriovorus HW1 and ABTW1 dosing protocol was optimised, with results indicating that the simultaneous application of B. bacteriovorus HW1 and ABTW1 at 0 h resulted in the greatest log reduction (5.66 and 3.97 log based on CFU/mL and GC/mL, respectively) in A. baumannii over the 96 h co-culture period. Similar log reductions (5.24 and 3.85 log reduction based on CFU/mL and GC/mL, respectively) were however, obtained for the initial dosing of B. bacteriovorus at 0 h, and addition of bacteriophage ABTW1 at 24 h. A lyophilised bacteriophage formulation (0.5 M sucrose and 1% gelatine) was then compared to the standard liquid bacteriophage inoculum, with B. bacteriovorus, in upscaled volume trials. However, as similar A. baumannii log reduction results were obtained, the standard bacteriophage liquid inoculum, with B. bacteriovorus, was assessed as a pre-treatment to 6 h SODIS. The B. bacteriovorus HW1-bacteriophage ABTW1 combination as well as the B. bacteriovorus HW1 only pre-treatment, both with SODIS, significantly reduced the A. baumannii cell counts (8.32 and 8.38 log, respectively) to below detection limit (BDL). Molecular analysis however, showed that A. baumannii persisted (~ 3 log reduction) after the application of all treatment protocols. It is thus recommended that the efficiency of the B. bacteriovorus-bacteriophage combination is further optimised to improve the lytic effect of both biological control agents, particularly the bacteriophage, on their prey.