In vitro antimicrobial activity, antibioresistance reversal properties, and toxicity screen of ethanolic extracts of Heracleum mantegazzianum Sommier & Levier (giant hogweed), Centaurea jacea L. (brown knapweed) and Chenopodium album L. (Pigweed): three invasive plants

Background and aim: Plants, including invasive ones, can play a significant role in the fight against antibiotic resistance and the search for new antimicrobials. The present study aimed at assessing the antimicrobial activity, antibioresistance reversal properties, and toxicity of 4 samples from invasive plants, namely leaves and flowers of Heracleum mantegazzianum, leaves of Chenopodium album and flowers of Centaurea jacea. Method: The extraction of active compounds was done with 80% ethanol, and the extraction yields were calculated. Antimicrobial activity was studied using the well diffusion method against Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 6538 and ATCC Candida albicans 10231. Minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC) were determined using the mircodilution method. The antibioresistance reversal properties was assessed using the checkerboard method and the toxicity of the extracts was studied using the larval form of the Greater Wax Moth (Galleria mellonella). Results: The mass yields were 11.9, 15.0, 18.2 and 21.5 respectively for C. jacea flower (CJF), H. mantegazzianum flower (HMF), H. mantegazzianum leaf (HML) and Chenopodium album leaf (CAL). The highest inhibition diameters (ID) were found with HMF, CAL, CJL and HML against S. aureus ATCC 6538 with 26.6±1.5, 21.6 ± 2.8, 21.0 ± 0.9 and 20.0 ± 1.4 mm respectively. Only CJL and HMF were active against E. coli ATCC 25922 with respective ID of 15.3 ±1.1 and 19.0 ± 1.7 mm. Except HMF (ID = 13.6 ± 2.0 mm), no other extract was active against C. albicans ATCC 10231. Moreover, HMF exhibited the lowest MIC (0.5 mg / ml) and the lowest MBC (1 and 4 mg / ml) against both S. aureus and E. coli. Regarding the synergy test, an additional effect (0.5≤FIC≤1) was found in almost all the combinations antibiotics + extracts excepted for HMF + (Kanamycin or Ampicillin) against S. aureus ATCC 6538 and CJF + Ampicillin against E. coli ATCC 25922 where we found synergy effect (FIC≤0.5). The median lethal doses (LD50s) of HMF, HML, CAL and CJF were 20.2, 0.58, 13.2 and 4.0 mg / ml respectively. Conclusion: Only the ethanolic extract of Heracleum mantegazzianum flowers showed noteworthy broad spectrum antimicrobial activity but further preclinical and clinical studies are required to evaluate the composition, the cytotoxicity and safety issues of these plant extracts and their combinations with common antibiotics before they can be recommended for antimicro