In vitro antibacterial activity of Loxostylis alata extracts and isolated compounds against Salmonella species.

BACKGROUND: Owing to antibiotic resistance, alternative antimicrobials from medicinal plants are receiving attention as leads for anti-infective agents. This study aimed to investigate selected tree species and their constituents for activity against bacterial foodborne pathogens, particularly Salmonella serovars. METHODS: Antibacterial activity of ten plant species was determined by serial microdilution against bacteria implicated in causing gastrointestinal ailments. Active compounds were isolated from Loxostylis alata using bioassay-guided fractionation. Antioxidant activity was determined using free-radical scavenging assays. Cytotoxicity and genotoxicity of the extracts was ascertained on Vero cells, and using the Ames assay respectively. RESULTS: Extracts had low to moderate MIC values from 0.04 to 2.5 mg/mL. Protorhus longifolia and Loxostylis alata were most active and L. alata had the highest selectivity index value (2.51) against Salmonella Typhimurium, as well as high antioxidant activity. Cytotoxicity values ranged from 0.02 to 0.47 mg/mL, while tested extracts were not genotoxic. Bioactive compounds isolated from L. alata included delicaflavone and a polymethoxyflavone. CONCLUSIONS: The Loxostylis alata leaf extract had strong activity against Salmonella serovars but isolated compounds were less active, indicating likely synergistic effects. Extracts of L. alata are promising candidates for development of antimicrobial preparations or food additives against microbial contamination.

In vitro bioactivity of the fractions and isolated compound from Combretum elaeagnoides leaf extract against selected foodborne pathogens.

ETHNOPHARMACOLOGICAL RELEVANCE: Combretum species are used traditionally for the treatment of diarrhoea, hookworm, fever, inflammation, pain and infectious diseases. Infections are commonly caused by the intake of food contaminated with foodborne pathogens. These are a significant concern in the food industry owing to their ability to form biofilms and cause food spoilage, despite the availability of modern food preservation techniques. Combretum elaeagnoides Klotzsch (Combretaceae) is used in southern African traditional medicine against infections and diarrhoea. AIM OF THE STUDY: This study evaluated the antimicrobial ability of C. elaeagnoides leaf fractions and the isolated compound quercetin-3-O-rhamnoside against a panel of foodborne pathogens, and biofilms formed by them. The samples were also assessed for their antioxidant activity and cytotoxicity. MATERIALS AND METHODS: Fractions prepared from the methanol extract of the leaves, and a bioactive compound (quercetin-3-O-rhamnoside) isolated from the ethyl acetate fraction were investigated for activity against nine reference and clinical strains of foodborne pathogens. The microdilution method was used to determine the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) of the fractions and compound. The inhibition of biofilm formation and the crystal violet staining assays were used to determine the antibiofilm efficacy. The DPPH (2, 2-diphenyl-1-picrylhydrazyl) assay and the 2, 2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) electron reduction assay were used to determine the antioxidant potential of the fractions and compound. The cytotoxicity was assessed using the 3-(4, 5-dimethylthiazolyl-2)-2,5-diphenyl tetrazolium bromide (MTT) colorimetric assay against Vero African monkey kidney cells. RESULTS: The fractions were active against all tested organisms, with MIC values ranging from 0.03 to 1.25 mg/mL. The best MBC was 0.63 mg/mL. All the fractions and the purified compound inhibited biofilm formation of Staphylococcus aureus and Salmonella Typhimurium, with percentage inhibition values greater than 50% at 1 mg/mL. The compound had very promising antibiofilm activity against Escherichia coli 1 (ATCC 25922) with percentage inhibition of >150%. The compound and fractions had good radical scavenging potential against the DPPH and ABTS radicals. Quercetin-3-O-rhamnoside and the fractions were relatively non-cytotoxic. CONCLUSION: The ability of the fractions and compound to reduce and inhibit biofilm biomass and their promising antioxidant potential provide motivation to further investigate the use of plants to protect food products from contamination, as well as to treat infections characterized by bacterial biofilms.

Antioxidant and Anti-Inflammatory Activities of Kigelia africana (Lam.) Benth.

Kigelia africana is used to manage inflammation among indigenous communities. We hypothesized that K. africana extracts contain phytoconstituents with good antioxidant and anti-inflammatory activities. The methanolic extract of K. africana fruits and Spathodea campanulata leaves (SPK04), K. africana aqueous fruit extract (KFM02), and K. africana acetone fruit extract (KFM05) were subjected to antioxidant and anti-inflammatory assays. Antioxidant activity was evaluated using the ABTS radical scavenging assay, and the MTT cell viability assay was used for cytotoxicity. The extracts were preincubated with enzymes and assayed for 15-LOX and COX-2 enzyme activity using an ELISA method. Nitric oxide (NO) inhibitory effect of the extracts was evaluated and measurement of proinflammatory cytokines (IL-1ß, TNF-α, and IL-6) and the anti-inflammatory cytokine (IL-10) was done using ELISA kits. SPK04 had the highest antioxidant activity with a mean inhibition of 99.37 ± 0.56% and an IC50 of 4.28 µg/mL. SPK04 and KFM05 did not inhibit 15-LOX as their IC50 values were >1000 µg/mL. All extracts were safe on Vero cells at the highest concentration (200 µg/mL) tested. KFM02 was the best inhibitor of NO production and had the highest cell viability at both the lowest (50 µg/mL) and highest concentrations (200 µg/mL). SPK04 was the best COX-2 inhibitor while KFM05 expressed the strongest suppression effect for IL-ß and IL-6. KFM02 did not inhibit IL-6 at the highest concentration (200 µg/mL). The order of suppression of TNF-α by the extracts differed across concentrations, KFM05 > SPK04 > KFM02 at 200 µg/mL, KFM02 > SPK04 > KFM05 at 100 µg/mL, and SPK04 > KFM02 > KFM05 at 50 µg/mL. All the tested extracts had no inhibitory effect against IL-10. SPK04, KFM05, and KFM02 had good antioxidant and anti-inflammatory activity and this supports their use as potential anti-inflammatory therapies. This study presents for the first time the antioxidant and anti-inflammatory activity of K. africana and S. campanulata polyherbal extract. It is also among the very few studies that have reported the inhibitory effect of cytokines IL-1ß, TNF-α, IL-6, and IL-10 by K. africana.

Antimicrobial Activity, Antioxidant Potential, Cytotoxicity and Phytochemical Profiling of Four Plants Locally Used against Skin Diseases.

Although orthodox medications are available for skin diseases, expensive dermatological services have necessitated the use of medicinal plants as a cheaper alternative. This study evaluated the pharmacological and phytochemical profiles of four medicinal plants (Drimia sanguinea, Elephantorrhiza elephantina, Helichrysum paronychioides, and Senecio longiflorus) used for treating skin diseases. Petroleum ether and 50% methanol extracts of the plants were screened for antimicrobial activity against six microbes: Bacillus cereus, Shigella flexneri, Candida glabrata, Candida krusei, Trichophyton rubrum and Trichophyton tonsurans using the micro-dilution technique. Antioxidant activity was conducted using 2,2-diphenyl-1-picryhydrazyl (DPPH) free radical scavenging and ß-carotene linoleic acid models. Cytotoxicity was determined against African green monkey Vero kidney cells based on the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) colorimetric assay. Spectrophotometric and Gas Chromatography-Mass Spectrometry (GC-MS) methods were used to evaluate the phytochemical constituents. All the extracts demonstrated varying degrees of antimicrobial potencies. Shigella flexneri, Candida glabrata, Trichophyton rubrum and Trichophyton tonsurans were most susceptible at 0.10 mg/mL. In the DPPH test, EC50 values ranged from approximately 6-93 µg/mL and 65%-85% antioxidant activity in the ß-carotene linoleic acid antioxidant activity model. The phenolic and flavonoid contents ranged from 3.5-64 mg GAE/g and 1.25-28 mg CE/g DW, respectively. The LC50 values of the cytotoxicity assay ranged from 0.015-5622 µg/mL. GC-MS analysis revealed a rich pool (94-198) of bioactive compounds including dotriacontane, benzothiazole, heptacosane, bumetrizole, phthalic acid, stigmasterol, hexanoic acid and eicosanoic acid, which were common to the four plants. The current findings provide some degree of scientific evidence supporting the use of these four plants in folk medicine. However, the plants with high cytotoxicity need to be used with caution.

In vitro antimicrobial effects of Hypoxis hemerocallidea against six pathogens with dermatological relevance and its phytochemical characterization and cytotoxicity evaluation.

ETHNOPHARMACOLOGICAL RELEVANCE: Hypoxis hemerocallidea (commonly known as African Potato) is popular in African traditional medicine. It is used in the management of diverse ailments including burns, wounds and skin-related diseases. AIM OF THE STUDY: The current study investigated the antimicrobial effects of Hypoxis hemerocallidea against six microorganisms associated with skin diseases. In addition, the antioxidant activity, phytochemical profiles and cytotoxicity of the bulb extracts were evaluated. MATERIALS AND METHODS: The antimicrobial activity of 50% methanol (MeOH) and petroleum ether (PE) extracts of Hypoxis hemerocallidea bulbs was tested against two bacterial and four fungal strains implicated in causing opportunistic skin-related diseases. Antioxidant potential of the extract was investigated via the 2,2-diphenyl-1-picryhydrazyl (DPPH) free radical scavenging assay and ß-carotene linoleic acid model. Phytochemical profiling of the 50% MeOH extract of Hypoxis hemerocallidea was done using spectrophotometric assay and Gas Chromatography-Mass Spectrometry (GC-MS). The extracts were also evaluated for cytotoxicity against African green monkey Vero kidney cell lines based on the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) colorimetric assay. RESULTS: Both 50% MeOH and PE extracts showed considerable inhibitory effects against all six microorganisms. The extracts were potent against Shigella flexneri and Trichophyton tonsurans with minimum inhibitory concentration (MIC) values less than 1 mg/ml. However, there was relatively poor antifungal activity against the other fungal strains. In the DPPH assay, the MeOH extract of the bulb had an EC50 of 29.8 µg/ml while 76.91% antioxidant activity was observed in the ß-carotene-linoleic acid model. The extract contained total phenolics (41 mg GAE/g) and flavonoids (10 mg CE/g). The GC-MS analysis of Hypoxis hemerocallidea bulb revealed 29 and 160 bioactive compounds for 50% MeOH and PE extracts, respectively. Based on the cytotoxicity, Hypoxis hemerocallidea had LC50 value of 210.9 ±â€¯18.4 and 95.5 ±â€¯13.3 µg/ml for PE and MeOH extracts, respectively. CONCLUSIONS: The bulb extracts of Hypoxis hemerocallidea exhibited good antimicrobial and antioxidant activities, which could be attributed to the presence of phenolics, flavonoids and the other bioactive compounds identified through GC-MS, making it a potentially effective cosmetic plant. These findings also account for the multi-pharmacological use of Hypoxis hemerocallidea in traditional medicine, especially related to skin diseases. The plant extracts can be considered as safe based on their LC50 values (< 20 µg/ml). However, other form of cytotoxicity studies need to be carried out on Hypoxis hemerocallidea, as well as in vivo tests, to confirm its safety and efficacy as a treatment for skin-related diseases.