Phage Therapy: Combating Evolution of Bacterial Resistance to Phages

Treatments for bacterial infections can be less effective due to toxicities, bacterial tolerance, or genetic resistance to antibacterial agents. The emphasis here is on combating genetic bacterial resistance to bacteriophages. Commonly described simply as phages, bacteriophages are the viruses of bacteria. As phage therapies, they are one of the oldest clinical treatments for bacterial infections. Thwarting bacterial evolution of resistance to phages, particularly during phage treatments, typically involves targeting more than one bacterial characteristic. This can be achieved serially, involving phage substitution after bacterial resistance has become problematic, something that is used especially during more personalized therapies. Substitution phages can be sourced in various ways. This includes as autophages, from phage banks, or via phage training—all as considered here—as well as through phage engineering. An alternative approach is preventing bacterial mutations from occurring at all. In addition, there is simultaneous targeting of multiple bacterial characteristics. These latter strategies include all of the following: using phages that target bacterial fitness or virulence determinants, employing individual phages that recognize multiple receptors, using phage cocktails, or applying phages in combination with antibiotics. This review discusses these different approaches for combating treatment resistance, highlighting various pros and cons.