Mycobacterium abscessus
Mycobacterium abscessus is among the most treatment-refractory human pathogens: a rapidly growing nontuberculous mycobacterium that causes chronic pulmonary, skin, and disseminated disease, especially in people with cystic fibrosis, bronchiectasis, or immunosuppression. It is intrinsically resistant to most antibiotic classes (beta-lactams, rifamycins, tetracyclines) and to many macrolides via inducible erm(41), so standard multidrug regimens last 12+ months, are poorly tolerated, and frequently fail to achieve culture conversion. This therapeutic dead-end is exactly where bacteriophages have found their highest-profile modern application: lytic mycobacteriophages kill the organism by a mechanism entirely independent of antibiotic resistance, can be engineered from temperate to strictly lytic forms, and have produced documented clinical responses in patients with no remaining options. M. abscessus is, in fact, the indication that produced the first-ever use of genetically engineered phages in a human.
How phages act here
Mechanism
Therapeutic mycobacteriophages adsorb to the mycobacterial cell envelope, inject their genome, and lyse the cell at the end of a productive replication cycle, a killing route unaffected by the antibiotic-resistance determinants that make M. abscessus so intractable. Strain specificity is the dominant practical constraint: phage host range is exquisitely narrow and varies enormously between isolates, so therapy is personalized — each patient's clinical isolate must be screened against a phage library to identify active lytic phages, and smooth-colony (glycopeptidolipid-coated) variants are frequently phage-resistant whereas rough variants are more susceptible. Engineering is central to the field: the canonical example is phage Muddy plus engineered derivatives of temperate phages BPs and ZoeJ in which the repressor gene was deleted (via BRED/recombineering) to convert them into obligately lytic, non-lysogenizing agents suitable for therapy. Cocktails of 2-3 phages are used to suppress emergence of resistance, and phages have been shown to penetrate and kill M. abscessus residing inside macrophages, addressing the intracellular niche that shields the organism from antibiotics. Phage-antibiotic synergy is an active mechanism of interest, with preclinical data showing enhanced clearance of drug-resistant M. abscessus when phages are combined with antibiotics. Key limitations are anti-phage neutralizing antibodies that can develop with intravenous dosing, and the small repertoire of phages with useful lytic activity against this species.
Where it stands
Current evidence
As of 2026 the evidence base is compassionate-use case reports and case series plus a formal protocolized study — there is no completed randomized controlled trial. The landmark first case (Dedrick et al., Nature Medicine 2019) treated a 15-year-old cystic fibrosis patient with disseminated drug-resistant M. abscessus after bilateral lung transplant using an engineered three-phage cocktail (Muddy + engineered BPs + engineered ZoeJ) IV for 32 weeks, with clinical improvement and no serious adverse events — the first therapeutic use of engineered phages in a human. A second detailed case (Nick et al., Cell 2022) at National Jewish Health treated refractory M. abscessus lung disease in severe CF with engineered phages IV, documenting phage-induced lysis, genetic stability of the pathogen, rising neutralizing-antibody titers that did not prevent benefit, and an explanted lung culture-negative for M. abscessus at transplant. The largest series (Dedrick et al., Clinical Infectious Diseases 2023) screened isolates from 200 patients, found lytic phages for only 55, treated 20 patients (IV and/or aerosolized) on compassionate use, observed no therapy-attributable adverse reactions, and saw favorable clinical or microbiologic responses in 11 of 20 — establishing both safety and the reality that many isolates have no available phage. Building on this, the multi-site POSTSTAMP study (Nick et al., J Cyst Fibros 2025) is an ongoing prospective FDA IND-based protocol giving 1-2 phages IV twice daily for 52 weeks to treatment-refractory CF patients with a comparison arm of patients lacking a phage match. The phage manufacturing and matching pipeline is run largely out of Graham Hatfull's laboratory at the University of Pittsburgh.
Evidence confidence: medium
The data
Key studies & trials
- Dedrick RM, Guerrero-Bustamante CA, Garlena RA, Russell DA, Ford K, Harris K, Gilmour KC, Soothill J, Jacobs-Sera D, Schooley RT, Hatfull GF, Spencer H. Engineered bacteriophages for treatment of a patient with a disseminated drug-resistant Mycobacterium abscessus. Nature Medicine. 2019;25(5):730-733. ↗
- 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. ↗
- 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, Martiniano SL, Lovell VK, et al. Trial design of bacteriophage therapy for nontuberculous mycobacteria pulmonary disease in cystic fibrosis: The POSTSTAMP study. Journal of Cystic Fibrosis. 2025;24(4):684-690. ↗
Who is working on it
Programs & centers
The possibility
If phage discovery can be scaled so that most M. abscessus isolates — not just the minority — have a matched lytic phage, personalized phage cocktails could become a standard adjunct that rescues patients for whom every antibiotic has failed, including those facing or recovering from lung transplant. Engineering pipelines that convert abundant temperate mycobacteriophages into potent lytic therapeutics, combined with phage-antibiotic synergy and formulations that reach intracellular bacteria, point toward off-the-shelf or rapidly customizable products rather than one-patient heroics. The POSTSTAMP protocol and similar IND-based studies are the bridge from compelling anecdote to the controlled efficacy data that could ultimately move phages into the M. abscessus treatment guidelines.