High Resolution Nanoscale Probing of Bacteriophages in an Inhalable Dry Powder Formulation for Pulmonary Infections

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Abstract
Use of powder phage formulations for the treatment of multidrug resistant pulmonary infections is gaining attention. To achieve therapeutic benefits, it is critical for phages to remain stable in the formulation. Assessment of phage stability relies on plaque assay (bioactivity), which requires powder samples to be reconstituted in liquid. The purpose of this study was to develop an innovative approach using photothermal-induced resonance enhanced atomic force microscopy infrared spectroscopy (AFM-IR) to assess the presence of phages and investigate their protein conformation in solid state. Staphylococcal phage S83 was spray dried with lactose and sodium stearate using spray drying. The phage powder recrystallized at 60% relative humidity (RH), so it was stored and handled below this RH. For the AFM-IR measurements spray dried Staphylococcal phage Sa83 powder was embedded in resin, followed by microtome sectioning. AFM-IR spectra collected from different regions within the microtomed sections revealed the presence of phage proteins with amide I and amide II bands at 1640 cm-1 and 1550 cm-1, respectively. The phages were confirmed to be stable as the plaque assay showed negligible titer reduction after spray drying. Our results thus demonstrated the utility of AFM-IR for characterization of nano-sized phages present in extremely low quantity in spray dried particles. These biologically active phages were shown to retain their physical and chemical integrity in the spray dried particles.
Funding Information
  • National Institute of Allergy and Infectious Diseases (R33AI121627)

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