Biology subjects

Hameed, H. M. A.

Publications and source records attributed to Hameed, H. M. A..

10 recordsLinked to original sources

bioRxiv2026

Identification and characterization of ethR and ethA genes impacting the sensitivity of Mycobacterium abscessus to ethionamide

Mycobacterium abscessus is a rapidly growing non-tuberculous mycobacterium with rising global incidence. This pathogen exhibits intrinsic resistance to most antibiotics, presenting a major public health threat. Ethionamide (ETH) requires bioactivation by monooxygenase EthA to form the active ETH-NAD adduct. We previously identified MAB_3513 (NudC) as a phosphohydrolase that confers intrinsic resistance to M. abscessus by hydrolyzing this adduct. However, deletion of nudC results in only partial susceptibility to ETH, indicating the existence of additional resistance mechanisms. This study identified MAB_0984 as the EthR regulator in M. abscessus. Deletion of ethR in a nudC knockout background ({Delta}{Delta}ethR) significantly enhanced ETH-NAD adduct accumulation, leading to hypersusceptibility to ETH. Notably, the {Delta}ethR mutant exhibited higher susceptibility than {Delta}nudC, demonstrating that EthR is a more dominant mediator of ETH resistance than NudC. Furthermore, MAB_0985 (EthA1) and MAB_0103 (EthA2) were identified as the primary EthAs in M. abscessus. Deletion of either gene alone or in combination in the {Delta}nudC reduced adduct formation and increased resistance, while the triple mutant {Delta}{Delta}ethA1{Delta}ethA2 restored wild-type resistance. Using an intergenic region-eGFP reporter system and quantitative reverse transcription-PCR, we demonstrated that EthR confers resistance by specifically suppressing ethA1 expression in M. abscessus. The Mycobacterium tuberculosis EthR inhibitor BDM31343 could boost the efficacy of ETH against M. abscessus by inhibiting EthR. Collectively, this study identified the ethR and ethA genes in M. abscessus for the first time and elucidated their role in mediating resistance to ETH. Therefore, EthR is a promising target for potentiating the efficacy of ETH against M. abscessus. Impact statementMycobacterium abscessus constitutes an escalating global health threat, primarily due to its intrinsic resistance to most antibiotics. This study identifies MAB_0984 (EthR) as a dominant resistance determinant that exerts a more profound impact on ETH susceptibility than the previously characterized NudC. We demonstrate that EthR mediates resistance by specifically repressing the expression of EthA1 (MAB_0985), one of the primary monooxygenases responsible for ETH bioactivation. The EthRMtb inhibitor BDM31343 potentiated the activity of ETH against M. abscessus through inhibition of the EthR. These findings elucidated the mechanism of ETH resistance in M. abscessus, identifying EthR as a promising target for boosting the efficacy of ETH against M. abscessus.

microbiology↗

bioRxiv2025

A division-associated envelope protein, MAB_2363, drives intrinsic resistance and virulence in Mycobacterium abscessus

Mycobacterium abscessus exhibits intrinsic resistance to conventional antibiotics, significantly limiting treatment options. Our previous studies established that MAB_2362 (SteA) is a key regulator of cell division that contributes to intrinsic resistance and virulence. Considering that SteA-like proteins often act alongside SteB counterparts, we hypothesized that the adjacent gene MAB_2363 encodes the corresponding SteB-like division regulator. In this study, we found that deletion of MAB_2363 significantly increased susceptibility to multiple antibiotics and disrupted cell wall permeability. Microscopy revealed striking cell division defects in the mutant, including elongated cell morphology and multiple septa. Subcellular localization of a GFP-MAB_2363 fusion protein demonstrated its enrichment at division septa, confirming its direct involvement in cell division. Deletion of MAB_2363 resulted in attenuated virulence, as evidenced by reduced bacterial survival in macrophages and murine infection models. To assess its functional relation with MAB_2362, we compared the single-deletion mutant of MAB_2363 with the single-deletion mutant of MAB_2362 and the double-deletion mutant of MAB_2362-MAB_2363. Notably, the phenotypes of the MAB_2363 mutant, including cell division defects, antibiotic susceptibility, and virulence, were markedly milder than those of the other two mutants. Collectively, these findings indicate that MAB_2363 functions as a secondary but essential division-associated factor that operates during cell division, thereby influencing intrinsic resistance and virulence in M. abscessus.

microbiology↗

bioRxiv2025

Targeting homologous recombination repair to potentiate fluoroquinolone efficacy in Mycobacterium abscessus

Synthetic antibiotics, fluoroquinolones (FQs), are extensively important treatment options for fast growing mycobacterial infections. However, their widespread use has led to decreased efficacy due to intrinsic or acquired resistance. FQs exhibit antimicrobial activity by stabilizing type II topoisomerases-generated DNA breaks, thereby inducing lethal double-strand breaks (DSBs) and leading to bacterial death. Escalating resistance among mycobacterial pathogens highlights the need to elucidate resistance mechanisms and identify novel strategies to restore or enhance the drug activity. Here, we revealed homologous recombination (HR) as a key determinant of FQ tolerance in Mycobacterium abscessus, a notoriously drug-resistant pathogen. Through a transposon mutagenesis screen, we identified that disruption of adnB - an HR-associated gene, markedly sensitized M. abscessus to FQs. This finding prompted a systematic dissection of DSB repair pathways in M. abscessus. Targeted deletion of HR core components (adnB, recO, recA, recR, ruvB) significantly increased FQ susceptibility in vitro, while inactivation of alternative DSB repair pathways - single-strand annealing (SSA) and non-homologous end joining (NHEJ) - had no effect, revealing a unique reliance on HR for FQ tolerance. Furthermore, the complementation of gene knock-out M. abscessus strains {Delta}adnB, {Delta}recO, {Delta}recA, {Delta}recR or {Delta}ruvB with the corresponding genes from M. abscessus, as well as homologous genes from Mycobacterium tuberculosis restored the resistance phenotype, indicating a conserved HR-dependent tolerance mechanism in M. abscessuss. In a murine infection model, genetic abrogation of HR significantly improved the therapeutic efficacy of FQs against M. abscessus, demonstrating translational relevance. Collectively, our findings position HR as a conserved and actionable vulnerability in M. abscessus, and provide a compelling rationale for developing HR-targeted adjuvant therapies to resensitize drug-refractory strains to FQ treatment. Impact statementFluoroquinolone (FQ) resistance poses a major challenge in the treatment of Mycobacterium abscessus infections. This study identifies homologous recombination (HR) as a key defense mechanism that limits FQ efficacy across multiple mycobacterial species. Genetic inhibition of HR not only sensitizes M. abscessus to FQs in vitro but also enhances antibiotic activity in vivo. These results highlight HR repair as a promising therapeutic target to potentiate FQ activity and combat drug resistance in M. abscessus infections.

molecular biology↗

bioRxiv2025

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

Mycobacterium abscessus (Mab) causes pulmonary diseases with limited treatment options due to its high level of intrinsic resistance to available drugs. Mab possesses complex and poorly understood drug resistance mechanisms. Identifying new drug targets and gaining a deeper understanding of drug resistance mechanisms are essential for discovering novel therapeutic alternatives. Here, we investigated the role of a putative sigma factor SigH in intrinsic multi-drug resistance in Mab. Mab SigH shares an 84% peptide sequence identity with Mycobacterium tuberculosis (Mtb) SigH, a well-known stress response protein and global transcriptional regulator. We constructed a sigH gene deletion strain of Mab ({Delta}sigH) and complemented strains by expressing either Mab sigH (CPMabsigH) or Mtb sigH (CPMtbsigH) in {Delta}sigH. The {Delta}sigH strain exhibited hypersensitivity to a broad range of antibiotics, including levofloxacin, moxifloxacin, tigecycline, tetracycline, amikacin, vancomycin, and rifabutin and all complemented strains restored the drug resistance phenotype. Additionally, {Delta}sigH showed increased sensitivity to oxidative and heat stress compared to the wild-type Mab and complemented strains. Transcriptomic analysis revealed that deletion of sigH disrupted the balance of gene expression, primarily elevating the expression of genes encoding YrbE and MCE family proteins and downregulating genes expressing ABC-type transporters, sigma and anti-sigma factors and other genes associated with antimicrobial resistance. Collectively, our findings indicate that SigH is a key regulator of global gene expression in response to environmental stresses, including antimicrobial treatment, and is crucial for the intrinsic drug resistance of Mab. SigH represents a promising target for the development of novel therapeutic strategies against Mab infections.

molecular biology↗

bioRxiv2024

High-throughput Screening of Compounds against Autoluminescent Nonreplicating Mycobacterium tuberculosis under Diverse Conditions

The screening of new anti-mycobacterial chemicals is primarily focused on inhibiting the active growing bacteria. However, a major challenge in tuberculosis control is the ability of Mycobacterium tuberculosis to enter a nonreplicating state for extended periods, rendering it resistant to many clinical drugs and complicating eradication efforts. Existing low-oxygen-recovery assays designed for screening compounds targeting nonreplicating M. tuberculosis have limitations, including the colony-forming unit counting for non-luminous M. tuberculosis and the instability of the free plasmid carrying luxAB genes in luminescent M. tuberculosis, along with exogenous substrate requirements for light producing. Moreover, these assays fail to accurately replicate the growth conditions of nonreplicating M. tuberculosis in vitro, thus resulting in less convincing results. To address these challenges, we have developed an autoluminescence-based, cholesterol-enriched culture evaluation model to assess 17 anti-tuberculosis drugs of different classes against nonreplicating M. tuberculosis. Our findings indicate that the relative light unit, measured in real-time, serves as a reliable surrogate marker for colony-forming unit, which typically becomes available one month later. This suggests the utility of our model for the rapid determination of drug susceptibility dynamically. The autoluminescent M. tuberculosis, harbouring luxCDABE gene cluster within its genome, can emit blue-green light stably and autonomously without requiring an external substrate supplement. The minimal inhibitory concentrations of all the drugs tested under anaerobic conditions are significantly different from that detected in aerobic environment. Our model allows for rapid, precise, and efficient assessment of drug activity under anaerobic conditions, thereby enabling a more comprehensive evaluation of anti-mycobacterial efficacy. Overall, our model represents a significant advancement in anti-tuberculosis drug discovery and pharmaceutical development.

microbiology↗

bioRxiv2024

Ilamycins are dual inhibitors of ClpX and ClpC1 involved in proteostasis in Mycobacteria

The mycobacterial caseinolytic protease (Clp) system has been recognized as a promising therapeutic target. In this study, we identified two novel ilamycin analogs, ilamycin E (ILE) and ilamycin F (ILF), both targeting the ClpC1 component of the ClpC1P1P2 proteasome. ILE potently disrupts ClpC1P1P2-mediated proteolysis, leading to delayed bactericidal activity, while ILF also binds ClpC1, albeit with lower affinity. Notably, we discovered a unique mutation in clpX and a novel insertion in clpC1, both conferring resistance to ILE and ILF in mycobacterium, validated by gene editing. Furthermore, ILE can also inhibit the proteolytic activity of ClpXP1P2 in a manner dependent on the substrates tag sequence and adaptor. This first demonstration of clpX- and clpC1-mediated ilamycin resistance underscores the potential of ilamycins to target multiple components of the Clp protease system, offering a novel dual-target strategy for combating mycobacterial infections.

microbiology↗

bioRxiv2024

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 {micro}g/mL). The embC gene knockout strain (Mab{Delta}embC) showed hyper-sensitive to ECH (MIC: 0.0078-0.0156 {micro}g/mL). The MICs of ECH-resistant strains screened based on the Mab{Delta}embC strain were 0.25-1 {micro}g/mL. Mutations were found in the EmbB, including Asp306Ala, Asp306Asn, Arg350Gly, Val555Ile, and Gly581Ser, which led to increased resistance to ECH when overexpressed in Mab{Delta}embC individually (0.25-0.5 {micro}g/mL). The EmbB mutants edited by the CRISPR/Cpf1 system became more resistant to ECH (MIC: 0.25-0.5 {micro}g/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. Impact StatementMycobacterium abscessus (Mab) is a rapidly growing, intrinsic multidrug-resistant Mycobacterium. This study demonstrated that echinomycin (ECH) has potent antibacterial activity against Mab, and the mechanism of ECH resistance to Mab is related to EmbB and EmbC. EmbB and EmbC can alter the sensitivity of Mab to ECH by altering the permeability of its cell wall. In addition, there is a functional complementary evolution between EmbB and EmbC to regulate sensitivity to ECH. Overall, our study provides a novel anti-Mab drug candidate ECH and a scientific foundation for developing effective strategies to prevent and control Mab.

microbiology↗

bioRxiv2024

Disrupting Homologous Recombination or Single-Strand Annealing Significantly Hinders CRISPR-Cas12a-Assisted Nonhomologous End-Joining Gene Editing Efficiency in Mycobacterium abscessus

Mycobacterium abscessus, a fast-growing, non-tuberculous mycobacterium resistant to most antimicrobial drugs, causes many types of serious infections in humans, posing a significant public health challenge. Currently, effective genetic manipulation tools for M. abscessus are still being developed, which hampers research and therapeutic development. However, the clustered regularly interspaced short palindromic repeats (CRISPR) - associated protein (Cas) systems have emerged as promising methods for generating highly specific double-strand breaks (DSBs) in its genome. These DSBs can be repaired by the error-prone nonhomologous end joining (NHEJ) mechanism, facilitating targeted gene editing. Here, our study marks a pioneering application of the CRISPR-NHEJ strategy in M. abscessus. Additionally, we discovered that NrgA from Mycobacterium marinum is crucial for the repair of DSBs caused by the CRISPR-Cas system in M. abscessus. Finally, contrary to previous findings, our study also indicates that inhibiting or overexpressing homologous recombination/single-strand annealing significantly decreases the efficiency of NHEJ repair in M. abscessus. This discovery challenges established perspectives and suggests that the NHEJ repair in M. abscessus may require the involvement of components from homologous recombination and single-strand annealing, demonstrating the complex interactions among the three DSB repair pathways in M. abscessus. Impact statementThere are still very few genetic manipulation tools available for Mycobacterium abscessus. Here we report the successful application of CRISPR-Cas12a-assisted nonhomologous end joining (NHEJ) in efficient gene editing in M. abscessus. Contrary to previous research suggesting that homologous recombination (HR) inhibition may enhance such editing efficiency in other Mycobacterium species, our results showed that disruption or overexpression of either HR or single-strand annealing not only failed to enhance but also significantly reduced the gene editing efficiency in M. abscessus. This suggests that NHEJ repair in M. abscessus may require components from both HR and single-strand annealing, highlighting a complex interaction among the DSB repair pathways in M. abscessus.

microbiology↗

bioRxiv2021

Sterilizing Effects of Novel Regimens Containing TB47, Clofazimine and Linezolid in a Murine Model of Tuberculosis.

Toxicity and inconvenience associated with the use of injectable drug-containing regimens for tuberculosis (TB) have made all-oral regimens a preferred alternative. Widespread resistance to fluoroquinolones and pyrazinamide makes it essential to identify new drug candidates and study their effects on current regimens for TB. TB47 is a pyrazolo[1,5-a]pyridine-3-carboxamide with powerful synergistic in vitro and in vivo activities against mycobacteria, especially with clofazimine. Here, we investigated the bactericidal and sterilizing activities of novel oral regimens containing TB47 + clofazimine + linezolid, and the potential roles of levofloxacin and/or pyrazinamide in such drug combinations. Using a well-established mouse model, we assessed the effect of these regimens on bacterial burden in the lung during treatment and relapse (4 months after stopping treatment + immunosuppression). Our findings indicate that the TB47 + clofazimine + linezolid + pyrazinamide, with/without levofloxacin, regimens had fast-acting (4 months) sterilizing activity and no relapse was observed. When pyrazinamide was excluded from the regimen, treatment times were longer (5-6 months) to achieve sterilizing conditions. We propose that TB47 + clofazimine + linezolid can form a highly sterilizing block for use as an alternative pan-TB regimen.

microbiology↗

bioRxiv2021

A recombinant selective drug-resistant M. bovis BCG enhances the bactericidal activity of a second-line tuberculosis regimen

Drug-resistant tuberculosis (DR-TB) results from infection by Mycobacterium tuberculosis strains resistant to at least rifampin or isoniazid. To improve the treatment outcome in DR-TB, therapeutic vaccines are considered an ideal choice as they can enhance pathogen clearance and minimize disease sequelae. To date, there is no therapeutic vaccine reported to be effective when combined with a chemotherapy regimen against DR-TB. The only available TB vaccine, the M. bovis BCG (BCG) is susceptible to several anti-TB drugs hence not a perfect option for therapeutic vaccination. Herein, we developed a recombinant BCG (RdrBCG) overexpressing Ag85B and Rv2628 with resistance to selected anti-TB drugs. When administered three times adjunct to a second-line anti-TB regimen in a classical murine model of DR-TB, the RdrBCG lowered lung M. tuberculosis colony-forming units by 1 log10. Furthermore, vaccination with the RdrBCG adjunct to TB chemotherapy minimized lung tissue pathology in mice. Most importantly, the RdrBCG maintained the exogenously inserted genes and showed almost the same virulence as its parent BCG Tice strain in severe combined immune-deficient mice. All these suggested that the RdrBCG was stable, safe and effective. Hence, the "recombinant" plus "drug-resistant" BCG strategy could be a useful concept for developing therapeutic vaccines against DR-TB.

microbiology↗