Aureocin A53 as a therapeutic agent against drug-resistant mycobacteria including M. tuberculosis and non-tuberculous strains

The global rise of tuberculosis (TB) and increasing drug resistance in Mycobacterium tuberculosis ( M. tuberculosis ) highlight the urgent need for novel antimycobacterial agents. Antimicrobial peptides (AMPs), particularly bacteriocins, offer promising therapeutic options or adjuncts for drug-resistant TB (DR-TB) owing to their unique mechanisms of action and low cytotoxicity. This study evaluated the antimicrobial activity of Aureocin A53, a bacteriocin produced by Staphylococcus aureus ( S. aureus ), against drug-resistant M. tuberculosis strains and non-tuberculous mycobacteria (NTM). Clinical S. aureus isolates were collected from laboratories in Isfahan, Iran. After phenotypic and biochemical identification, isolates were screened for bacteriocin production using the well diffusion assay. Strains showing inhibition zones > 5 mm were selected for PCR detection of the aucA gene. Aureocin A53 was purified using ammonium sulfate precipitation, Tricine-SDS-PAGE, and reversed-phase high-performance liquid chromatography (RP-HPLC). Its antimicrobial efficacy was tested against drug-resistant M. tuberculosis strains (isoniazid-resistant, rifampicin-resistant, and MDR), the reference strain M. tuberculosis H37Rv, and several NTM species ( M. avium , M. kansasii , M. fortuitum , M. chelonae ) using the resazurin microtiter assay (REMA) for minimum inhibitory concentration (MIC) determination and the proportional method. Among 70 clinical S. aureus isolates from high-TB-burden regions, 48 exhibited antibacterial activity (> 3 mm inhibition zones), and PCR confirmed the aureocin A53 gene in one isolate. Following purification, Aureocin A53 demonstrated potent activity against M. tuberculosis H37Rv (MIC = 128 µg/ml), isoniazid-resistant M. tuberculosis (MIC = 256 µg/ml), and multidrug‑resistant clinical strains. Notably, Aureocin A53 also inhibited non‑tuberculous mycobacteria ( M. fortuitum , M. chelonae ) at concentrations of 128–256 µg/ml, while showing no cytotoxicity toward THP‑1 macrophages at MIC‑proximate doses. The highest compound cytotoxicity toward THP‑1 macrophages was observed at 1024 µg/mL after 72 h exposure. Aureocin A53 exhibits potent preclinical efficacy against drug-resistant mycobacteria with low cytotoxicity, supporting its use as a combination therapy adjunct. Further in vivo validation is warranted to advance TB treatment.