Indigenous Medicinal Plants as Biofilm Inhibitors for the Mitigation of Antimicrobial Resistance

Abstract

The majority of indigenes in the rural areas of Ghana use herbal medicines for their primary health care. In this study, an ethnobotanical survey was undertaken to document medicinal plants used by traditional healers in the Ejisu-Juaben district in the Ashanti region of Ghana to treat infections and to further investigate the antibiofilm formation properties of selected plants in resisting pathogenic bacteria. Seventy medicinal plants used by traditional practitioners for the treatment of skin infections and wounds were documented from the ethnobotanical survey. Forty out of the seventy plants were collected and their methanol extracts evaluated for antimicrobial activity by the agar diffusion assay. Extracts that showed antibacterial activity were tested for biofilm inhibitory activity, and the most active plant was subsequently purified to obtain the active constituents. Biofilm formation was significantly mitigated by petroleum ether, ethyl acetate, and methanol extracts of Holarrhena floribunda stem bark. Bioassay-guided fractionation of an alkaloidal extract prepared from the methanol fraction led to the isolation of three steroidal alkaloids, namely, holonamine, holadienine, and conessine. The isolated compounds demonstrated varying degrees of biofilm formation inhibitory properties. The current study reveals that screening of indigenous medicinal plants could unravel potential leads to salvage the declining efficacy of conventional antibiotics. Holarrhena floribunda stem bark extract has strong biofilm formation inhibition properties, which could be attributed to the presence of steroidal alkaloids.

Figure 1

Map of Ejisu-Juaben district (Source: Ghana Statistical Service).

Figure 2

: Selected plants for biofilm formation inhibitory activity. (a) Trichilia lanata (MTL). (b) Grossera vignei (MGV). (c) Acacia ataxacantha (MAA). (d) Bridelia stenocarpa (MBS). (e) Albizia ferruginea (MAF). (f) Holarrhena floribunda (MHF). (g) Triplochiton scleroxylon (MTS). (h) Anogeissus sericea (MAS).

Figure 3

Photomicrographs of adhering bacterial cells (biofilms) stained with 0.1% crystal violet on a glass slide after 24 hours, observed at ×100: (a) S. aureus. (b) S. pyogenes. (c) E. coli. (d) P. aeruginosa. (e) K. pneumoniae.

Figure 4

(a-b) Graphs showing the effect of different concentrations of extracts on the amount of biofilm formed (optical density-OD) by S. aureus. MBS, Bridelia stenocarpa; MAS, Anogeissus sericea; MTL, Trichilia lanata; MGV, Grossera vignei; MAA, Acacia ataxacantha; MAF, Albizia ferruginea; MHF, Holarrhena floribunda; MTS, Triplochiton scleroxylon; CIP, ciprofloxacin.

Figure 5

Steroidal alkaloids from the stem bark of H. floribunda. (a) Holonamine. (b) Holadienine. (c) Conessine.

Figure 6

6 (a-b) Graphs showing the effect of different concentrations of fractions and isolated compounds on the amount of biofilm formed (optical density-OD) by S. aureus. EHE : EtOAc fraction; PHE: pet-ether fraction; MHE : MeOH fraction; AKL: alkaloidal fraction; HF1A: holonamine; HF1B: holadienine; HF1C: conessine.