Mycobacterium avium complex (MAC)
Mycobacterium avium complex (MAC) lung disease is a chronic, slowly progressive nontuberculous mycobacterial infection that often requires 12-18+ months of multi-drug macrolide-based therapy, yet frequently fails to achieve durable culture conversion and is increasingly complicated by macrolide resistance and poor antibiotic penetration into granulomas, biofilms, and macrophages. The intrinsic drug resistance, slow growth, and intracellular/biofilm lifestyle of M. avium leave a large unmet need for adjunctive options. Bacteriophages (mycobacteriophages) are well suited because they are self-amplifying, strain-targeted lytic agents that can reach mycobacteria in niches where antibiotics struggle, and a clinical pipeline already exists for related NTM (notably M. abscessus). For M. avium specifically, the evidence is still early-stage and largely built on a single well-documented compassionate-use case plus preclinical phage discovery, so phages are best framed as a promising experimental adjunct rather than an established therapy.
How phages act here
Mechanism
Mycobacteriophages bind species- and strain-specific cell-surface receptors and lyse the bacterium, so therapy must be personalized: each clinical M. avium isolate is screened against a phage panel to find lytic matches, and active phages are often combined into cocktails to broaden coverage and suppress resistance. A recurring practical constraint is colony morphotype, smooth (often glycopeptidolipid-coated) variants are typically resistant or poorly killed in liquid culture, while rough variants are more phage-susceptible, mirroring the pattern characterized in M. abscessus. Phages such as Muddy and engineered/forward-genetics derivatives of temperate phages (deleting repressor/integration genes to force a strictly lytic, non-lysogenic cycle, conceptually a CRISPR/genome-engineering-adjacent strategy) have been deployed clinically; the M. avium pulmonary case was treated with the naturally lytic broad-host-range phage Muddy. Mechanistically attractive features for MAC include penetration of biofilms and the potential to act on intracellular/macrophage-resident bacilli, with phage-antibiotic synergy reported in NTM models where phage-encoded products can potentiate antibiotic activity; because a single phage was sufficient in the one M. avium case, full cocktails may be needed mainly where single-phage coverage or resistance is a concern.
Where it stands
Current evidence
Evidence for M. avium specifically is at the single-case-report plus preclinical stage as of 2026, there is no completed or registered randomized phage trial for MAC pulmonary disease. The anchor clinical datapoint is the Dedrick/Hatfull compassionate-use cohort (Clinical Infectious Diseases, 2023): of 200 patients screened and 20 treated, only 1 had pulmonary M. avium (a cystic fibrosis patient, treated intravenously with the single phage Muddy), with a favorable response, FEV1 improvement >15% in the first month, time-to-culture-positivity lengthening, and consecutive AFB cultures showing no growth at 21 and 25 weeks. The remainder of that cohort and the broader clinical program (including the 2022 Cell engineered-phage report and the POSTSTAMP prospective study) center on M. abscessus, not MAC. Preclinically, lytic phages active against M. avium subsp. paratuberculosis with cross-species host range to other M. avium/NTM strains have been isolated (Golla et al., 2024), and review syntheses (Bonacorsi et al., 2024; Ash, Moon & Jang, 2025) describe M. avium phage activity and characterize the field as moving from novelty to cautious optimism while flagging immunologic (neutralizing-antibody) and biological barriers. No phage product is FDA/EMA-approved for any NTM indication; all human use to date is compassionate/expanded-access.
Evidence confidence: low
The data
Key studies & trials
- Dedrick RM, Smith BE, Cristinziano M, et al. Phage Therapy of Mycobacterium Infections: Compassionate Use of Phages in 20 Patients With Drug-Resistant Mycobacterial Disease. Clinical Infectious Diseases. 2023;76(1):103-112. ↗
- Nick JA, Dedrick RM, Gray AL, et al. Host and pathogen response to bacteriophage engineered against Mycobacterium abscessus lung infection. Cell. 2022;185(11):1860-1874.e12. ↗
- Bonacorsi A, Ferretti C, Di Luca M, Rindi L. Mycobacteriophages and Their Applications. Antibiotics (Basel). 2024;13(10):926. ↗
- Golla AC, Chaumontet J, Vande Voorde R, Danelishvili L. Discovery of Mycobacterium avium subsp. paratuberculosis Lytic Phages with Extensive Host Range Across Rapid- and Slow-Growing Pathogenic Mycobacterial Species. Antibiotics (Basel). 2024;13(11):1009. ↗
Who is working on it
Programs & centers
The possibility
If phage banks and rapid isolate-matching mature, a person with refractory MAC lung disease could one day have a sputum sample screened against a library of lytic mycobacteriophages within days, then receive a tailored inhaled or intravenous cocktail that clears bacilli hiding in biofilms and macrophages where antibiotics stall. Engineered, strictly lytic phages and rationally chosen phage-antibiotic pairings could shorten the brutal multi-year drug regimens MAC now demands and rescue patients with macrolide-resistant disease who currently have few options. The remaining hurdles, expanding the thin repertoire of phages active against slow-growing, smooth-morphotype M. avium and managing neutralizing-antibody responses, are exactly the problems that registries, phage engineering, and the first prospective NTM phage trials are now built to solve.