EmbB and EmbC Regulate the Sensitivity of Mycobacterium abscessus to Echinomycin

Treatment of Mycobacterium abscessus (Mab) infection is a major challenge due to its intrinsic resistance to most available drugs. It is thus imperative to find new anti-Mab drugs. In this study, we investigated the activity and intrinsic resistance mechanism of echinomycin (ECH) against Mab. ECH is active against Mab (MIC: 2 μg/mL). The embC gene knockout strain (MabΔembC) showed hyper-sensitive to ECH (MIC: 0.0078-0.0156 μg/mL). The MICs of ECH-resistant strains screened based on the MabΔembC strain were 0.25-1 μg/mL. Mutations were found in the EmbB, including Asp306Ala, Asp306Asn, Arg350Gly, Val555Ile, and Gly581Ser, which led to increased resistance to ECH when overexpressed in MabΔembC individually (0.25-0.5 μg/mL). The EmbB mutants edited by the CRISPR/Cpf1 system became more resistant to ECH (MIC: 0.25-0.5 μg/mL). The permeability of gene-edited and overexpressed Mab strains was reduced, as shown by the ethidium bromide accumulation assay, but it was still significantly higher than that of the parent Mab. To summarize, our study demonstrates that ECH has a strong anti-Mab activity and confirms that EmbB and EmbC are related to the sensitivity of Mab to ECH. EmbB mutation may partially compensate for the function of EmbC. ### Competing Interest Statement The authors have declared no competing interest.