Antibacterial properties of extracts of Ludwigia peploides subsp. montevidensis and Ludwigia grandiflora subsp. hexapetala during their cycle of development

• Study of antibacterial properties of extracts from two Ludwigia species.
• Expression of the antibacterial activity in roots, stems, leaves and flowers.
• Expression of the antibacterial activity during the cycle of development of the plants.
• Comparison of this activity to those of classical antibiotics.
• Interest of the results for a therapeutical study.

Ludwigia peploides subsp. montevidensis and Ludwigia grandiflora subsp. hexapetala, form aquatic dense stands, which cause major ecological and economical problems in many aquatic ecosystems in France. However, these species are known to release allelopathic compounds. Here, antibacterial properties were assessed on samples from different plant organs, during June, July and August for L. peploides and throughout the development period, from April to September, for L. grandiflora. The disk diffusion method was used here to screen dimethylsulfoxide plant extracts against 5 Gram positive and 9 Gram negative bacterial strains. The sensitivity of the bacteria tested to L. grandiflora extracts was greater than that to those of L. peploides. Maximum antibacterial activity was measured in June, July or August, depending on the plant organ, principally in leaf and flower extracts. Activity also varied according to the bacterial strains tested. A principal component analysis (PCA) showed that sensitivity to the plant extracts did not depend on whether the bacterial strains are Gram positive or Gram negative. Thus, we found that a Gram positive strain, Staphylococcus aureus (CIP 76.25), and a Gram negative strain, Salmonella enterica (DSM 10062), were similar in sensitivity. Antibacterial activities of certain leaf or flower extracts of both species of Ludwigia were revealed superior to those of several classic antibiotics tested. The interest of this study concerns the therapeutical potential of the two Ludwigia species.