The small non-coding RNA B11 regulates multiple facets of Mycobacterium abscessus virulence

An O-methylflavone from Artemisia afra kills non-replicating hypoxic Mycobacterium tuberculosis

ETHNOPHARMACOLOGICAL RELEVANCE

African wormwood (Artemisia afra Jacq. ex Willd.) has been used traditionally in southern Africa to treat illnesses causing fever and was recently shown to possess anti-tuberculosis activity. As tuberculosis is an endemic cause of fever in southern Africa, this suggests that the anti-tubercular activity of A. afra may have contributed to its traditional medicinal use.

AIM OF THE STUDY

Tuberculosis, caused by Mycobacterium tuberculosis (Mtb), is a deadly and debilitating disease globally affecting millions annually. Emerging drug-resistant Mtb strains endanger the efficacy of the current therapies employed to treat tuberculosis; therefore, there is an urgent need to develop novel drugs to combat this disease. Given the reported activity of A. afra against Mtb, we sought to determine the mechanisms by which A. afra inhibits and kills this bacterium.

MATERIALS AND METHODS

We used transcriptomics to investigate the impact of Artemisia spp. extracts on Mtb physiology. We then used chromatographic fractionation and biochemometric analyses to identify a bioactive fractions of A. afra extracts and identify an active compound.

RESULTS

Transcriptomic analysis revealed that A. afra exerts different effects on Mtb compared to A. annua or artemisinin, suggesting that A. afra possesses other phytochemicals with unique modes of action. A biochemometric study of A. afra resulted in the isolation of an O-methylflavone (1), 5-hydroxy-7-methoxy-2-(4-methoxyphenyl)chromen-4-one, which displayed considerable activity against Mtb strain mc26230 in both log phase growth and metabolically downshifted hypoxic cultures.

CONCLUSIONS

The present study demonstrated that an O-methylflavone constituent of Artemisia afra explains part of the activity of this plant against Mtb. This result contributes to a mechanistic understanding of the reported anti-tubercular activity of A. afra and highlights the need for further study of this traditional medicinal plant and its active compounds.

Preclinical murine models for the testing of antimicrobials against Mycobacterium abscessus pulmonary infections: Current practices and recommendations

Mycobacterium abscessus, a rapidly growing nontuberculous mycobacterium, is increasingly recognized as an important pathogen of the human lung, disproportionally affecting people with cystic fibrosis (CF) and other susceptible individuals with non-CF bronchiectasis and compromised immune functions. M. abscessus infections are extremely difficult to treat due to intrinsic resistance to many antibiotics, including most anti-tuberculous drugs. Current standard-of-care chemotherapy is long, includes multiple oral and parenteral repurposed drugs, and is associated with significant toxicity. The development of more effective oral antibiotics to treat M. abscessus infections has thus emerged as a high priority. While murine models have proven instrumental in predicting the efficacy of therapeutic treatments for M. tuberculosis infections, the preclinical evaluation of drugs against M. abscessus infections has proven more challenging due to the difficulty of establishing a progressive, sustained, pulmonary infection with this pathogen in mice. To address this issue, a series of three workshops were hosted in 2023 by the Cystic Fibrosis Foundation (CFF) and the National Institute of Allergy and Infectious Diseases (NIAID) to review the current murine models of M. abscessus infections, discuss current challenges and identify priorities toward establishing validated and globally harmonized preclinical models. This paper summarizes the key points from these workshops. The hope is that the recommendations that emerged from this exercise will facilitate the implementation of informative murine models of therapeutic efficacy testing across laboratories, improve reproducibility from lab-to-lab and accelerate preclinical-to-clinical translation.

Evolution and emergence of Mycobacterium tuberculosis

Tuberculosis (TB) remains one of the deadliest infectious diseases in human history, prevailing even in the 21st century. The causative agents of TB are represented by a group of closely related bacteria belonging to the Mycobacterium tuberculosis complex (MTBC), which can be subdivided into several lineages of human- and animal-adapted strains, thought to have shared a last common ancestor emerged by clonal expansion from a pool of recombinogenic Mycobacterium canettii-like tubercle bacilli. A better understanding of how MTBC populations evolved from less virulent mycobacteria may allow for discovering improved TB control strategies and future epidemiologic trends. In this review, we highlight new insights into the evolution of mycobacteria at the genus level, describing different milestones in the evolution of mycobacteria, with a focus on the genomic events that have likely enabled the emergence and the dominance of the MTBC. We also review the recent literature describing the various MTBC lineages and highlight their particularities and differences with a focus on host preferences and geographic distribution. Finally, we discuss on putative mechanisms driving the evolution of tubercle bacilli and mycobacteria in general, by taking the mycobacteria-specific distributive conjugal transfer as an example.

A methoxylated flavone from Artemisia afra kills Mycobacterium tuberculosis

Tuberculosis, caused by Mycobacterium tuberculosis (Mtb), is a deadly and debilitating disease globally affecting millions annually. Emerging drug-resistant Mtb strains endanger the efficacy of the current combination therapies employed to treat tuberculosis; therefore, there is an urgent need to develop novel drugs to combat this disease. Artemisia afra is used traditionally in southern Africa to treat malaria and recently has shown anti tuberculosis activity. This genus synthesizes a prodigious number of phytochemicals, many of which have demonstrated human health effects. Transcriptomic analysis revealed that A. afra exerts different effects on Mtb compared to A. annua or the well-known antimalarial artemisinin, suggesting other phytochemicals present in A. afra with unique modes of action. A biochemometric study of A. afra resulted in the isolation of a methoxylated flavone (1), which displayed considerable activity against Mtb strain mc26230. Compound 1 had an MIC of 312.5 μg/mL and yielded no viable colonies after 6 days of treatment. In addition, 1 was effective in killing hypoxic Mtb cultures, with no viable cultures after 2 days of treatment. This suggested that A. afra is a source of potentially powerful anti-Mtb phytochemicals with novel mechanisms of action.