antimicrobial activity, antibioresistance reversal properties, and toxicity screen of ethanolic extracts of Sommier and Levier (giant hogweed), L. (brown knapweed), and L. (Pigweed): Three invasive plants.

Background: Plants, including invasive ones, can play a significant role in the fight against antibiotic resistance and the search for new antimicrobials.

Aims: The present study aimed at assessing the antimicrobial activity, antibioresistance reversal properties, and toxicity of four samples from invasive plants, namely, (leaves and flowers), (leaves), and (flowers).

Methods: The extraction of active compounds was done with ethanol (80%, ) and the extraction yields were calculated. Antimicrobial activity was studied using the agar-well diffusion method against ATCC 25922, ATCC 6538, and ATCC 10231. Minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC) were determined using the mircodilution method. The antibioresistance reversal properties were assessed using the checkerboard method and the toxicity of the extracts was studied using the larval form of the Greater Wax Moth ().

Results: The mass yields were 11.9, 15.0, 18.2, and 21.5, respectively, for flower (CJF), flower (HMF), leaf (HML), and leaf (CAL). The highest inhibition diameters (ID) were found with HMF, CAL, CJF, and HML against with 26.6, 21.6, 21.0, and 20.0 mm, respectively. Only CJF and HMF were active against with respective ID of 15.3 and 19.0 mm. Except HMF (ID = 13.6 ± 2.0 mm), no other extract was active against . Moreover, HMF exhibited the lowest MIC (0.5 mg/ml) and the lowest MBC (1 and 4 mg/ml) against both and . Regarding the synergy test, an additional effect [0.5 ≤ fractional inhibitory concentration (FIC) ≤ 1] was found in almost all the combinations antibiotics + extracts excepted for HMF + (Kanamycin or Ampicillin) against and CJF + Ampicillin against 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 HMFs showed noteworthy broad spectrum antimicrobial activity.