Dual Predation by Bacteriophage and Bdellovibrio bacteriovorus Can Eradicate Escherichia coli Prey in Situations where Single Predation Cannot

Abstract

Bacteria are preyed upon by diverse microbial predators, including bacteriophage and predatory bacteria, such as Bdellovibrio bacteriovorus. While bacteriophage are used as antimicrobial therapies in Eastern Europe and are being applied for compassionate use in the United States, predatory bacteria are only just beginning to reveal their potential therapeutic uses. However, predation by either predator type can falter due to different adaptations arising in the prey bacteria. When testing poultry farm wastewater for novel Bdellovibrio isolates on Escherichia coli prey lawns, individual composite plaques were isolated containing both an RTP (rosette-tailed-phage)-like-phage and a B. bacteriovorus strain and showing central prey lysis and halos of extra lysis. Combining the purified phage with a lab strain of B. bacteriovorus HD100 recapitulated haloed plaques and increased killing of the E. coli prey in liquid culture, showing an effective side-by-side action of these predators compared to their actions alone. Using approximate Bayesian computation to select the best fitting from a variety of different mathematical models demonstrated that the experimental data could be explained only by assuming the existence of three prey phenotypes: (i) sensitive to both predators, (ii) genetically resistant to phage only, and (iii) plastic resistant to B. bacteriovorus only. Although each predator reduces prey availability for the other, high phage numbers did not abolish B. bacteriovorus predation, so both predators are competent to coexist and are causing different selective pressures on the bacterial surface while, in tandem, controlling prey bacterial numbers efficiently. This suggests that combinatorial predator therapy could overcome problems of phage resistance. IMPORTANCE With increasing levels of antibiotic resistance, the development of alternative antibacterial therapies is urgently needed. Two potential alternatives are bacteriophage and predatory bacteria. Bacteriophage therapy has been used, but prey/host specificity and the rapid acquisition of bacterial resistance to bacteriophage are practical considerations. Predatory bacteria are of interest due to their broad Gram-negative bacterial prey range and the lack of simple resistance mechanisms. Here, a bacteriophage and a strain of Bdellovibrio bacteriovorus, preyed side by side on a population of E. coli, causing a significantly greater decrease in prey numbers than either alone. Such combinatorial predator therapy may have greater potential than individual predators since prey surface changes selected for by each predator do not protect prey against the other predator.

Predatory bacteria as living antibiotics – where are we now?

“…The host specificity and rapid acquisition of bacterial resistance to phage needs to be considered; the broad bacterial prey range and the lack of simple resistance mechanisms of predatory bacteria give it an advantage in comparison. Interestingly, recent work by Hobley and colleagues has highlighted the combinatorial power of using predatory bacteria alongside phage [95]; the separate kinetics of phage susceptibility and Bdellovibrio predation allowed greater bacterial cell killing of E. coli in certain conditions.…”

The antibiotic crisis: How bacterial predators can help

“…With this in mind, researchers are making efforts to determine the sensitivity of Bdellovibrio against antibiotics [127] , and more research must be carried out to determine its ability to grow on antibiotic-inactivated cells and the AR mechanisms developed by the predator. Recently, experiments using Bdellovibrio and prey-specific bacteriophages eradicated E. coli when preyed upon by both predators, demonstrating the potential of this innovative co-therapy as a future alternative antibacterial treatment that would reduce the selection for single predator-specific resistance [128] .…”

Predation strategies of the bacterium Bdellovibrio bacteriovorus result in overexploitation and bottlenecks

“…To our knowledge, Varon & Zeigler (13) and Hobley, Summers et al (18) are the only studies of predation kinetics where experimental data were used to infer parameters of a model. Varon & Zeigler (13) used a relative of Bdellovibrio, the marine strain BM4, and Photobacterium leiognathi as prey.…”

“…P. leiognathi can grow at rates of up to 0.2 h -1 (30), however, nothing beyond the study by Varon and Zeigler ( 13) is known about the growth kinetics of strain BM4. Hobley, Summers et al (18) used the type strain of Bdellovibrio bacteriovorus (HD100), with E. coli as the prey species, which are the species assumed in our study. Predictions from the Hobley, Summers et al study were used to calculate default values for the attack kinetics.…”

“…Similarly, Hobley et al (7), Baker et al (16) and Said et al (17) included a predator-prey complex and a Holling type I functional response. Hobley, Summers et al (18) fitted a series of models, with a separate bdelloplast stage and various predator functional responses, to data from batch culture predation by either Bdellovibrio, a bacteriophage or both, and found a synergistic effect from dual predation. Two further models have been developed by Hol et al (19) and Dattner et al (20), both including spatial structure.…”