Bacteriophage infection and killing of intracellular Mycobacterium abscessus

is a nontuberculous mycobacteria that contributes to the decline and death of patients with lung diseases such as cystic fibrosis and other muco-obstructive airway diseases. is challenging to treat due to its extensive antibiotic resistance and ability to survive inside mammalian cells. An alternative to antibiotics is the therapeutic use of bacteriophages (phages). There are recent cases of phage therapy being used to treat infections in people under compassionate-use conditions. However, little is known about the ability of phages to kill bacteria, such as , which reside in an intracellular environment. Here, we used strains and phages from recent phage therapy cases to determine if phages can enter mammalian cells and if they can infect and kill intracellular . Using fluorescence microscopy, we demonstrate phage uptake by macrophages and lung epithelial cells, and we further demonstrate phage infection of intracellular with fluorescent reporter phages. Transmission electron microscopy was additionally used to image phage infection of intracellular . Together, these findings provide the first visualizations of phage- interactions in an intracellular environment. Finally, we show that phage treatment can significantly reduce the intracellular burden of in a manner that depends on both the specific phage and mammalian cell type involved. These results demonstrate the potential to use phage therapy to treat intracellular bacteria, specifically , while also highlighting the importance of prescreening phage therapy candidates for activity in an intracellular environment.