| dc.description.abstract | Introduction: A host of opportunistic infections add to the present endemic state of some
already existing infections with most of the morbidity and mortality in AIDS cases resulting
from opportunistic infections. Opportunistic infections are caused by pathogens such as
bacteria, viruses, protozoa or fungi in individuals whose immune system is compromised.
Most opportunistic infections are however well managed to some extent with the available
specific standard drug regimens. The emergence of fungi and bacteria as ever-increasing
causes of morbidity and mortality as well as the complications in their drug management has
led to the need for exploration, discovery and development of new antifungal and
antibacterial drugs with better safety and efficacy profile. Search for antifungal and
antibacterial agents from natural sources is one area that is currently drawing a lot of
attention.
Problem statement and study justification: Despite the availability and use of the standard
antifungal and antibacterial drugs, some therapeutic problems still persist, in particular the
emergence of new pathogenic fungal species, variable drug bioavailability, drug toxicity, lack
of desired and appropriate dosage form preparations, significant drug interactions for some
agents and development of resistance or breakthrough infections. The search for new
molecules from other sources such as plants that are useful as lead models for and/or as
medicines that can handle these setbacks must continually be pursued.
Study objectives: The main objective of this study was to investigate the potential antibacterial
and antifungal activity of ten selected plants of medical importance with a view to
providing scientific basis for the traditional use in treating of mouth and skin fungal
infections. The specific objectives were to determine the in vitro antibacterial and antifungal
activity of crude extracts; determine and isolate the constituents of the two most bioactive
plants, Alectra sessiliflora Vahl. Kuntze and Blumea axillaris Lam. DC.; elucidate the
structure of the isolated compounds and to determine the in vitro antifungal and antibacterial
activity of the isolated compounds.
Methodology: The following plants were screened in the study: Sida tenuicarpa Vollesen
(Malvaceae), Spilanthes mauritiana (Rich. ex Pers.) DC. (Asteraceae), Fuerstia africana
T.C.E.Fries (Labiatae), Chamaecrista mimosoides (L.) Greene (Caesalpiniaceae), Alectra
sessiliflora (Vahl.) Kuntze (Scrophulariaceae), Blumea axillaris (Lam.) DC. (Asteraceae),
Cucumis anguria L. var. longaculeatus J.H.Kirkbride (Cucurbitaceae), Hibiscus fuscus
Garcke (Malvaceae),Physalis peruviana L.(Solanaceae) and Lantana trifolia L.
(Verbenaceae). Preparation of reagents was carried out as per published protocols or
val idated methods. In preliminary investigations the chloroform, methanol and water extracts
were screened for antimicrobial activity against microbes of medical importance. The
antibacterial and antifungal activity of the plant extracts, at fixed specified concentrations per
well, against standardized inoculum of Staphylococcus aureus and Candida albicans,
respectively, was tested by the disk diffusion method. The bio-autography procedure was
then employed to determine the active fractions of the active extracts. Arising from the
screening results, Alectra sessiliflora Vahl. Kuntze and Blumea axillaris Lam. DC were
investigated further through Soxhlet extraction, fractionation, compound isolation and
characterisation. The fractionation of plant extracts was carried out using a combination of
various physical techniques namely solvent extraction and open column chromatography on
silica gel, thin layer chromatography being used to follow purity of isolated fractions,
macroporous resin and size exclusion chromatography. Chemical structure elucidation was
based on spectroscopic data iacluding IR, lH-NMR, 13C_NMR and MS and GC-MS.
Results and discussion: Thirty extracts were obtained from the ten plant species. Of the
extracts, 90 % inhibited bacterial growth, while 70 % inhibited fungal growth when screened
in vitro. With the exception of only one extract, water extract of Chamaecrista mimosoides,
all the zones of inhibitions diameters were less than those of the standard reference drugs,
chloramphenicol and nystatin, tested at 50 ug/well, A total of 89 spots were visualized using
the 3-(4, 5-dimethylthiazo-2-yl)-2, 5-diphenyltetrazolium bromide (MIT) spray reagent on
the bio-autographs of the thirteen most active extracts with 52 spots (58.4 %) showing
antimicrobial bioactivity. Five compounds, a sphingoid base, P-sitosterol; two phenolic acids,
p-coumaric acid and 3, 4 dihydroxybenzoic acid; a flavonoid, luteolin were isolated from
Alectra sessiliflora Vahl. Kuntze. In addition,two phytosterols, stigmasterol and p-sitosterol
as well as two liquid isolates were realised from Blumea axillaris Lam. DC. The liquid
isolates were found to compromise of a total of eight major constituents, 2-methyl-4-
hydroxycyclobutanone, tert-pentylamine, diethylacetoacetamide, 2-(1, I-dimethylethyl)-l ,4-
dimethoxybenzene, 2-dodecanone , 4-methylester octanoic acid, butanoic acid octyl ester and
9-tetradece-l-ol acetate. Of the isolated compounds, p-coumaric acid, 3,4-dihydroxybenzoic
acid, luteolin and the two liquid isolates obtained from Blumea axillaris exhibited appreciable
antibacterial and antifungal activity (MIC<25.0 ug/well) against tested bacteria Pseudomonas
aeruginosa, Escherichia coli and Bacillus pumilus as well as the fungi Candida albicans,
Aspergillus niger and Cryptococcus neoformans.
Conclusion and recommendations: All the screened plant extracts showed some level of
antimicrobial activity, with some plants possessing antifungal constituents some of which
were isolated. From literature, this is the first report of in vitro antibacterial and anti-fungal
activity and isolation of the bioactive compounds from Alectra sessiliflora Vahl. Kuntze.
The isolation of the stigmasterol and p-sitosterol from B. axillaris Lam. DC.is also reported
for the first time although -the compounds had earlier been reported from other Blumea
species. These compounds could possibly be a basis of chemotaxonomy of the genus. The
composition of the two liquid isolates realised is reported from B. axil/aris for the first time.
The antibacterial and antifungal activity reported in this study may be due to some of the
isolated compounds acting either singly or in combination. The results obtained from this
work may inform the continued use of the plants as herbal remedies or use of the isolated
constituents as possible lead compounds in the development of new antifungal agents.
Further scientific work is however recommended especially toxicity studies and use of
combinational and computational techniques in synthesis of new leads that may lead to more
useful compound to tackle the current or any future emerging fungal infections. | en_US |
