Intracellular localisation of Mycobacterium tuberculosis affects antibiotic efficacy

To be effective, chemotherapy against tuberculosis (TB) must kill the intracellular population of Mycobacterium tuberculosis (Mtb). However, how host cell environments affect antibiotic accumulation and efficacy remains elusive. Pyrazinamide (PZA) is a key antibiotic against TB, yet its behaviour is not fully understood. Here, by using correlative light, electron, and ion microscopy to image PZA at the subcellular level, we investigated how human macrophage environments affect PZA activity. We discovered that PZA accumulates heterogeneously between individual bacteria in multiple host cell environments. Crucially, Mtb phagosomal localisation and acidification increase PZA accumulation and efficacy. By imaging two antibiotics commonly used in combined TB therapy, we showed that bedaquiline (BDQ) significantly enhances PZA accumulation by a host cell mediated mechanism. Thus, intracellular localisation and specific microenvironments affect PZA accumulation and efficacy; explaining the potent in vivo efficacy compared to its modest in vitro activity and the critical contribution to TB combination chemotherapy. ### Competing Interest Statement The authors have declared no competing interest. * (Mtb) : Mycobacterium tuberculosis (TB) : tuberculosis (INH) : isoniazid (RIF) : rifampicin (ETB) : ethambutol (PZA) : pyrazinamide (BDQ) : bedaquiline (POA) : pyrazinoic acid (CLEIM) : correlative light electron and ion microscopy (OD600nm) : optical density 600 nm (MDM) : Human monocyte-derived macrophages (MOI) : multiplicity of infection (SEM) : Scanning Electron Microscopy (NanoSIMS) : nanoscale secondary ion mass spectrometry ( C max) : maximum serum concentration (BafA1) : Bafilomycin-A1 (ConA) : Concanamycin A.