Abstract
Protea caffra is used as a diarrhoeal remedy in South African herbal medicine, however, its pharmacological properties remain largely unknown. In the present study, extracts from different Protea caffra organs were screened against drug-sensitive and -resistant diarrhoeagenic pathogens using the microdilution assay (minimum inhibitory concentration, MIC). Twig extracts (70% methanol, MeOH) of the plant were purified and the resultant fractions screened for antibacterial properties (MIC). The chemical profiles of the fractions were determined by Gas Chromatography-Mass Spectrometry (GC-MS), while ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) was used to quantify the phenolic acids in the plant. The mutagenic properties of bioactive extracts were assessed using the Ames test. The extracts demonstrated weak-moderate antibacterial properties (MIC: 0.3–0.6 mg/mL). A cold ethyl acetate fraction of MeOH twig extract exhibited significant antibacterial properties (MIC = 0.078 mg/mL) against Enterococcus faecalis. The presence of antibacterial compounds (1-adamantane carboxylic acid, heptacosanol, levoglucosan, nonadecanol) in the plant was putatively confirmed based on GC-MS analysis. Furthermore, UHPLC-MS/MS analysis revealed varying concentrations of phenolic acids (0.08–374.55 µg/g DW). Based on the Ames test, the extracts were non-mutagenic thereby suggesting their safety. To a certain degree, the current study supports the traditional use of Protea caffra to manage diarrhoea among local communities in South Africa.
Highlights
Diarrhoea is an intestinal disorder characterised by the passage of frequent loose or watery stools in a period of 24 h [1]
In South Africa, Protea caffra Meisn (Proteaceae) is among the common plants utilised by local herbalists for treating diarrhoea [14]
It is possible that the antibacterial compounds in Protea caffra water extracts occurred in very low, sub-lethal concentrations resulting in poor antibacterial activity (Table S1)
Summary
Diarrhoea is an intestinal disorder characterised by the passage of frequent loose or watery stools in a period of 24 h [1]. In 2015 alone, diarrhoeal diseases caused an estimated 1.3 million deaths worldwide and were the fourth leading causes of death among children under the age of 5 years [2]. Plants 2020, 9, 1331 are used to manage diarrhoeal symptoms [5]. In Europe, diarrhoea is managed traditionally using plants such as Matricaria chamonilla (dry flowering decoctions), Solanum tuberosum (tuber decoctions) and Vaccinium myrtillus (fruit decoctions) [9]. African herbs commonly used to treat the disease include Elephantorrhiza elephantina (root decoctions), Euphorbia hirta (leaf macerate), Heinsia pulchella (root bark decoction), Ozoroa insignis (bark decoctions), Psidium guajava (leaf infusions), Sclerocarya birrea (leaf and bark infusions), Solanum supinum (root decoction), Terminalia sericea (root infusions) and Ximenia caffra (roof decoctions) [10,11,12,13]. In South Africa, Protea caffra Meisn (Proteaceae) is among the common plants utilised by local herbalists for treating diarrhoea [14]
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