The stress response factor SigH mediates intrinsic resistance to multiple antibiotics in Mycobacterium abscessus

Mycobacterium abscessus (Mab) is a pathogenic fast-growing mycobacterium with complex, poorly understood drug resistance mechanisms and limited treatment options. This warrants renewed efforts to dissect resistance mechanisms and identify novel targets. Here, we report that disruption of the putative sigma factor sigH in Mab results in hypersensitivity to levofloxacin, moxifloxacin, tigecycline, tetracycline, amikacin, vancomycin, and rifabutin. Mab SigH shares 84% peptide sequence identity with Mycobacterium tuberculosis (Mtb) SigH, a well-known stress-response protein and global transcriptional regulator. Complementation of the knockout strain (Δ sigH ) with Mab sigH or its Mtb homolog restored the drug resistance phenotype. Additionally, Δ sigH showed increased sensitivity to oxidative and heat stress compared to the wild-type (WT) Mab and complemented strains. Transcriptomic analysis revealed that the deletion of sigH disrupted the balance of gene expression, primarily elevating the expression of genes encoding YrbE and MCE family proteins and downregulating genes encoding ABC-type transporters, sigma and anti-sigma factors, and other genes associated with antimicrobial resistance. Notably, Δ sigH accumulated more ethidium bromide and displayed cell-elongation phenotypes, both partially reversed by complementation. In addition, a native sigH promoter driving green fluorescent protein (GFP) produced 10-fold higher fluorescence in WT than in Δ sigH , suggesting that the presence of SigH drives higher GFP expression . Collectively, our findings identify SigH as a key regulator of global gene expression that links stress adaptation, cell-envelope homeostasis, and intrinsic multidrug resistance in Mab, hence representing a promising target for the development of novel therapeutics against Mab infections. IMPORTANCE Mycobacterium abscessus (Mab) causes severe acute and chronic lung infections. The intrinsic drug resistance mechanisms of Mab remain poorly understood, posing significant therapeutic challenges. Here, we examined the role of the putative sigma factor SigH in intrinsic multidrug resistance in Mab. Mab SigH shares 84% amino acid identity with M. tuberculosis . SigH is a well-known stress response regulator. Transcriptomic analysis revealed that the deletion of sigH disrupted the balance of gene expression, primarily elevating the expression of genes encoding YrbE and MCE family proteins and downregulating genes encoding ABC-type transporters, sigma and anti-sigma factors, and other genes associated with antimicrobial resistance. A native sigH promoter driving green fluorescent protein (GFP) produced 10-fold higher fluorescence in wild type than in Δ sigH , suggesting that the presence of SigH drives higher GFP expression. Thus, SigH emerges as a central regulator integrating stress adaptation, envelope homeostasis, and multidrug resistance, offering a promising target for novel anti-Mab therapies.