Artemisia annua and Artemisia afra extracts exhibit strong bactericidal activity against Mycobacterium tuberculosis

Abstract

Ethnopharmacological relevance: Emergence of drug-resistant and multidrug-resistant Mycobacterium tuberculosis (Mtb) strains is a major barrier to tuberculosis (TB) eradication, as it leads to longer treatment regimens and in many cases treatment failure. Thus, there is an urgent need to explore new TB drugs and combinations, in order to shorten TB treatment and improve outcomes. Here, we evaluated the potential of two Asian and African traditional medicinal plants, Artemisia annua, a natural source of artemisinin (AN), and Artemisia afra, as sources of novel antitubercular agents.

Aim of the study: Our goal was to measure the activity of A. annua and A. afra extracts against Mtb as potential natural and inexpensive therapies for TB treatment, or as sources of compounds that could be further developed into effective treatments.

Materials and methods: The minimum inhibitory concentrations (MICs) of A. annua and A. afra dichloromethane extracts were determined, and concentrations above the MICs were used to evaluate their ability to kill Mtb and Mycobacterium abscessus in vitro.

Results: Previous studies showed that A. annua and A. afra inhibit Mtb growth. Here, we show for the first time that Artemisia extracts have a strong bactericidal activity against Mtb. The killing effect of A. annua was much stronger than equivalent concentrations of pure AN, suggesting that A. annua extracts kill Mtb through a combination of AN and additional compounds. A. afra, which produces very little AN, displayed bactericidal activity against Mtb that was substantial but weaker than that of A. annua. In addition, we measured the activity of Artemisia extracts against Mycobacterium abscessus. Interestingly, we observed that while A. annua is not bactericidal, it inhibits growth of M. abscessus, highlighting the potential of this plant in combinatory therapies to treat M. abscessus infections.

Conclusion: Our results indicate that Artemisia extracts have an enormous potential for treatment of TB and M. abscessus infections, and that these plants contain bactericidal compounds in addition to AN. Combination of extracts with existing antibiotics may not only improve treatment outcomes but also reduce the emergence of resistance to other drugs.

Keywords: Artemisia afra; Artemisia annua; Artemisinin; Mycobacterium abscessus; Mycobacterium tuberculosis; Tuberculosis.

Figure 1.. Artemisia extracts exhibit strong bactericidal activity against M. tuberculosis.

A. The minimum inhibitory concentrations (MICs) of AN, established TB drugs, and plant extracts were determined. For plant extracts, the AN concentrations present in the extract MICs are shown. B. M. tuberculosis mc²6230 was incubated in the presence of 150 μg/mL or 300 μg/mL of pure AN, or A. annua extract containing equivalent concentrations of AN. C. M. tuberculosis mc²6230 was incubated in the presence of several first- and second-line TB drugs. D and E. M. tuberculosis mc²6230 (D) or Erdman (E) were exposed to 150 μg/mL of pure AN or A. annua extract containing equivalent concentrations of AN or A. afra at equivalent dry weight as the A. annua extract. Plant extract concentrations were ~4X their MICs. 2.5% DMSO was included as a control.

Figure 2.. Artemisia extracts have different impacts on M. abscessus and M. smegmatis.

The strains were incubated in presence of 300 μg/mL (A) or 600 μg/mL (B) of pure AN, or A. annua extract containing equivalent concentrations of AN, or A. afra at equivalent dry weight as the A. annua extract. 2.5% DMSO was included as a control.