Mutant and Recombinant Phages Selected from Coevolution Conditions Overcome Phage-Resistant Listeria monocytogenes.

Bacteriophages (phages) are currently available for use by the food industry to control the foodborne pathogen Although phage biocontrols are effective under specific conditions, their use can select for phage-resistant bacteria that repopulate phage-treated environments. Here, we performed short-term coevolution experiments to investigate the impact of single phages and a two-phage cocktail on the regrowth of phage-resistant and the adaptation of the phages to overcome this resistance. We used whole-genome sequencing to identify mutations in the target host that confer phage resistance and in the phages that alter host range. We found that infections with phages LP-048, LP-125, or a combination of both select for different populations of phage-resistant bacteria with different regrowth times. Phages isolated from the end of the coevolution experiments were found to have gained the ability to infect phage-resistant mutants of and strains previously found to be broadly resistant to phage infection. Phages isolated from coinfected cultures were identified as recombinants of LP-048 and LP-125. Interestingly, recombination events occurred twice independently in a locus encoding two proteins putatively involved in DNA binding. We show that short-term coevolution of phages and their hosts can be utilized to obtain mutant and recombinant phages with adapted host ranges. These laboratory-evolved phages may be useful for limiting the emergence of phage resistance and for targeting strains that show general resistance to wild-type (WT) phages. is a life-threatening bacterial foodborne pathogen that can persist in food processing facilities for years. Phages can be used to control in food production, but phage-resistant bacterial subpopulations can regrow in phage-treated environments. Coevolution experiments were conducted on a phage-host system to provide insight into the genetic variation that emerges in both the phage and bacterial host under reciprocal selective pressure. As expected, mutations were identified in both phage and host, but additionally, recombination events were shown to have repeatedly occurred between closely related phages that coinfected This study demonstrates that evolution of phages can be utilized to expand the host range and improve the long-term efficacy of phage-based control of This approach may also be applied to other phage-host systems for applications in biocontrol, detection, and phage therapy.