Genetic Signatures from Adaptation of Bacteria to Lytic Phage Identify Potential Agents To Aid Phage Killing of Multidrug-Resistant Acinetobacter baumannii.

With the increasing morbidity and mortality rates associated with multidrug-resistant bacteria, interest in bacteriophage therapy has been revived. However, bacterial resistance to phage infection threatens the usefulness of phage therapy, especially its inclusion in modern medicine. Multidrug-resistant Acinetobacter baumannii is a top-priority pathogen requiring urgent intervention and new therapeutic approaches, such as phage therapy. Here, we experimentally adapted A. baumannii WHG40004 to its lytic phage P21 and thereafter isolated a phage-resistant bacterial mutant, named Ev5-WHG. We then aimed to identify potential agents to aid phage killing of Ev5-WHG by analyzing its genome and that of the wild-type strain. The enriched Gene Ontology (GO) analysis based on genetic alterations in minor alleles and mutations showed that pathways such as zinc ion transport and cell membrane synthesis could play certain roles in phage resistance. Remarkably, the combination of zinc acetate and P21 showed increased bactericidal effect on Ev5-WHG. Significantly also, we showed that P21 completely prevented the growth of wild-type WHG40004 in the presence of antibiotics (meropenem and imipenem). The results from this study indicate that the analysis of phage resistance signatures during adaptation of bacteria to a lytic phage can inform the choice of agents to work cooperatively with phage to limit and/or reverse resistance. This approach could be important for guiding future successful phage therapy. IMPORTANCE Bacteriophages have proven very useful as alternative therapeutic agents in combating multidrug-resistant bacterial infections; however, bacterial resistance to phages threatens their use. In this study, we showed a new strategy of leveraging genetic signatures that accompany phage resistance in bacteria to predict agents that can be used with lytic phages to combat multidrug-resistant Acinetobacter baumannii. Significantly, this approach was helpful in suggesting the use of zinc acetate to reduce resistance in phage-resistant bacteria, as well as the use of phage with antibiotics meropenem and imipenem to prevent resistance in a wild-type strain of multidrug-resistant A. baumannii. The approach of this study will be helpful for improving the outcome of phage therapy and in overcoming antimicrobial resistance.