An efficient method for visualizing the plaques of Bdellovibrio bacteriovorus

Bdellovibrio bacteriovorus preys upon other Gram-negative bacteria. This obligate predator is recognized as a living antibiotic to control the rising problem of antibiotic resistance. Plaque forming units (PFU) counting is commonly used to determine the viable numbers of B. bacteriovorus. However, nearly 3-days incubation is always necessary for getting the single, obvious plaques on the double layer agar plate. This time-consuming procedure greatly impedes the purification and enumeration efficiency of B. bacteriovorus. In this work, we evaluated the advantages of fluorescent prey on the plaque visualization of the predator. Our study reveals that plaques of the B. bacteriovorus have already formed before they could be monitored by eyes on the double layer agar plate. The regular single plaques are easily observed under the enhanced background of fluorescent prey lawn in 1.5 days, reducing nearly half of the time consumption in the purification and enumeration of B. bacteriovorus. In addition, it also provides some paradigms for modeling and testing the subtle predation process on the solid medium. IMPORTANCEThe viability of predator Bdellovibrio bacteriovorus is typically suggested by the lysis of the prey bacteria on the double layer agar plate. However, long period incubation is necessary to get single obvious plaques of B. bacteriovorus. Here, we found that plaques are already generated before it can be monitored by eyes. The plaques are obvious on the enhanced background of the double layer agar plate in the presence of fluorescent prey under UV light. We confirmed that the utilization of fluorescence labeled prey bacteria reduces the time spent on the isolation, purification, and enumeration of the predator B. bacteriovorus on the double layer agar plate.