Burkholderia pseudomallei is a significant public health and biothreat pathogen that is recognized as a potential Weapon of Mass Destruction (WMD) due to its resistance to treatment. Moreover, its natural prevalence means that it can infect deployed Warfighters by acquisition from natural environments or by nefarious means. Antibiotic treatment of B. pseudomallei infections and post-exposure prophylaxis are hampered by the bacterium’s intrinsic and acquired antimicrobial resistance (AMR). Efflux pumps, specifically those of the resistance nodulation cell division (RND) family, are major AMR factors and the sole known multidrug resistance (MDR) determinants in B. pseudomallei. These pumps often compromise the therapeutic use of current drugs and those in pre-clinical or clinical development. As such, novel strategies aimed at disarming efflux pumps hold much promise for greatly improving existing but rather limited therapeutic regimens, or perhaps even affording new treatment strategies, thus providing novel Counter WMD (C-WMD) approaches. The objective of our project is to examine the feasibility of exploiting B. pseudomallei-specific bacteriophages that use surface exposed outer membrane (OM) channel proteins of RND efflux pumps. We anticipate that mutations in the efflux pumps enabling evasion of phage infection will potentiate the activity of previously ineffective antibiotics. The overall goal of the initial work was to identify phages that bind to the OM channel proteins - OprA and OprC - of the clinically significant AmrAB-OprA and BpeEF-OprC efflux pumps. This required the construction of isogenic mutants expressing or lacking AmrAB-OprA and mutants expressing or lacking BpeEF-OprC in the Select Agent exempt B. pseudomallei strain Bp82. Deletion of the OprA gene alone does not completely eliminate antibiotic efflux activity so efforts were focused on phages that utilize the OprC pump. Also, to eliminate identifying phages that utilize LPS as a receptor, we also generated a LPS deletion strain in the OprC expressing background. This strain was then employed for phage screening and characterization. Soil samples from Thailand, where B. pseudomallei is endemic, were seeded with the OprC-pump-utilizing variant to amplify bacteriophage growth before filtration and top agar plaque assays were performed. Of the fifty soil samples seeded, plaques were observed on seven plates. Resulting plaques were further amplified and screened against the OprC-deletion variants to remove phages with non-OprC-binding-specific activity. Twenty-two total plaque samples were cross-screened against these variants, and will be additionally tested with the LPS-deletion variants to further cull the collection before full characterization. Phage growth dynamics are evaluated by monitoring bacterial biomass on a multi-mode plate reader and one-step growth curves to determine burst size. Further characterization will include host-range studies, TEM, and sequencing. The results of this project are expected to advance C-WMD science in that they move forward a novel aspect of phage therapy for B. pseudomallei infections that can potentially be developed into a specific therapy immune to traditional AMR mechanisms for infected Warfighters.