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Traditional usage
In the Eastern Cape, the Zulu, Tswana, and Xhosa communities soak the bark and twigs
in hot water which is used as a wash, lotion, or dressing for the treatment of wounds
(
Grierson & Afolayan, 1999; Watt & Breyer-brandwijk, 1962). Other medicinal properties
include the use of the bark and roots to treat bladder ailments (
Pitso & Lebese, 2014).
Melianthus comosus Vahl.
Melianthus comosus commonly known as the honey flower or the “touch me not” (kruid-
jie-roer-my-nie) belongs to the Melianthaceae family. This erect shrub can grow up to
12 m tall with multiple branches covered in stellate hairs. The pinnately compound
leaves can grow up to 20 cm long and are arranged alternately with four to seven pairs of
opposite leaflets. The leaflets are oblong to lanceolate with toothed margins. The raceme
inflorescences originate from the leaf axils and can grow up to 10 cm long. Flowers have
four, unequal petals which are red in color. Fruits are bladder shaped, winged, and have a
membranous capsule. The seeds are ovoid, black, or dark brown and grow between 3 and
6mm (
Weber, 2017). This species is distributed throughout Namibia and in the dry inte-
rior regions of seven South African provinces and in neighboring Lesotho (
Harris, 2004).
Traditional usage
A poultice and a decoction prepared from the leaves of Melianthus comosus are used to
treat bed sores, septic wounds, and to reduce swelling (
Mabona, Viljoen, Shikanga,
Marston, & Van Vuuren, 2013
). Harris (2004) also reported the use of the leaf poultice and
decoction for bruising, backache, and rheumatoid arthritis in the joints. A study in the
south-eastern Karoo reported that the species is applied topically to reduce inflammation
in the leg and for various skin ailments. Other uses include applying the leaves as a poul-
tice, and bathing or soaking in water in which the plant has been boiled, to treat pain asso-
ciated with legs, knees, and the back (
van Wyk, 2008). The Xhosa’s make a paste prepared
from the leaves or a tincture prepared from the root bark or the leaves to treat wounds
associated with snake bites. Additionally, a dec oction is used to treat slow-healing
wounds, and a dressing prepared from the leaf paste is used to treat sores and reduce
swelling caused by bruises (
Watt & Breyer-brandwijk, 1962).
Plectranthus fruticosus L’He
´
r
Plectranthus fruticosus otherwise known as the skunk-leaf is a 11.5 m high, semiwoody,
branched perennial belonging to the Lamiaceae family. This species can be found along
rocky shaded areas and forests occurring from the Western Cape, Limpopo and
Mpumalanga and Swaziland borders, particularly at altitudes higher than 1000 m. Cross-
sections of the branches are characteristically square with leaves arranged oppositely. The
dark green leaves are broadly ovate, toothed along the margin, and slightly velvety, reach-
ing 120150 mm in diameter. The leaves have a characteristic dark green venation. The
leaf petiole is green and grows to lengths of 6080 mm. The inflorescence is an erect pani-
cle reaching up to 300 mm in length and made up of around 600 mauve, blue-purple
164 4. Medicinal plants used in South Africa as antibacterial agents for wound healing
Medicinal Plants as Anti-infectives
flowers, generally occurring as six flowers per node. Flowering occurs from mid-March to
early May. The calyx is green with a purple mouth and the seeds or nutlets are 1.5 mm
long and brown in color occurring at the base of the calyx (
Harrower, 2010; Jodamus &
Notten, 2002
).
Traditional usage
Plectranthus fruticosus is used in Romanian traditional medicine for its healing and
soothing properties, particularly for burns of the skin. The stems are used as a repellent
for flies and are often rubbed along windows to deter entry. In South Africa, this species
is often used for its ornamental or esthetic properties (
Lukhoba, Simmonds, & Paton,
2006
). It has further been reported that the Khoi-San and Cape Dutch used the fresh leaves
for the treatment of open wounds (
van Wyk, 2008).
Polystichum pungens (Kaulf.) C. Presl
Polystichum pungens, known as the forest shield fern or the prickly shield fern, belonging
to the Dryopteridaceae family, is found distributed throughout South Africa, such as in
the Eastern and Western Cape, Limpopo, Mpumalanga and KwaZulu-Natal, and is found
in Swaziland. It is confined to forest areas with elevations ranging from 600 to 1350 m,
such as Table Mountain and the foothills of the Drakensberg. The rhizomes lie along the
surface of the ground resulting in the formation of a clonal stand and therefore a shrubby
growth appearance. The leaves can reach a height of up to 1 m long and are dark green in
appearance (
Foden & Potter, 2005; Roux, 2004).
Traditional usage
In the Eastern Cape, it was reported that the dried fronds were pulverized into a pow-
der and applied on wounds. Similarly, the fresh fronds are ground and used as a poultice
(
Grierson & Afolayan, 1999). The southern Sotho use a decoction prepared from the
rhizome as an enema for intestinal worms in humans and to treat bot fly infestations in
horses (
Watt & Breyer-brandwijk, 1962).
Sutherlandia frutesce ns (L.) R.Br.
Sutherlandia frutescens, better known by its common name, cancer bush, forms part of
the Fabaceae family and has recently been transferred to the genus Lassertia, thereby it has
been renamed to Lasseria frutescens (L.) It is classified as a shrub that is soft-wooded and
can reach heights of up to 1 m. The gray-green colored leaves are pinnately compound
with the leaflets reaching lengths of between 4 and 10 mm. During spring to mid-summer
(September-December), bright orange flowers, up to 35 mm long, form, which in turn
develop into large bladder-like fruits. It is widely distributed throughout the drier regions
of southern Africa, such as Namibia and Botswana. In South Africa it can be found in
the Western and Eastern Cape, including the Karoo, as well as KwaZulu-Natal and
Mpumalanga (
Xaba & Notten, 2003).
165South African medicinal plant species with activity against wound-associated bacteria
Medicinal Plants as Anti-infectives
Traditional usage
It has been reported that the Khoisan and the Nama people, the original Cape inhabi-
tants, used a decoction of the species as a wash to treat wounds. A decoction has also
been used as a wash to treat ailments relating to the eyes. It is extensively used for numer-
ous other health-related problems and diseases such as cancer (which the common name
is derived from), colds, bronchitis, TB, arthritis, liver ailments, hemorrhoids, and several
other disorders (
Xaba & Notten, 2003).
Urtica urens L.
Urtica urens more commonly known as the small nettle belongs to the Urticaceae family.
This plant is considered a weed and is often found in cultivated fields, gardens, and
orchards. This species has a wide distribution spanning from the temperate regions of
Europe, California in the United States of America, the tropics in Africa, and is widespread
throughout South Africa. The species is an erect, branched, annual shrub growing up to
65 cm high. The four-angled stem is sparsely covered in stinging hairs. The olive-green leaves
are in an opposite arrangement, with a 35 cm long petiole. The dense, monecious flowers
occur as a cyme inflorescence, blooming in March to May months. The nut is compressed,
ovate, smooth, and often shiny and is between 14.2 mm3 11.4 mm (
Aswal, 1972).
Traditional usage
In the south-eastern Karoo, the powdered leaves are applied topically to burn wounds
(
van Wyk, 2008). The Zulus use this species as an aphrodisiac, whilst in the south-western
Cape a bark infus ion is ingested to treat inflammation, pain in the bladder, and internal
bleeds as well as to stimulate lactation. An infusion is applied externally for the treatment
of burns. The ground plant powder is used as a snuff to treat nose bleeds and made into
a sirup using brown sugar for the treatment of whooping cough. A warm compress pre-
pared using an infusion is applied to different tumors (
Watt & Breyer-brandwijk, 1962). A
study by Al-Bakri and Afifi (2007) recorded the use of the leaves to have antirheumatic,
antispasmodic properties and is used as a diuretic.
Compounds present in plants traditionally used for wound healing in South
Africa
Although several of the tested plant extracts (Table 4.1) have not shown significant anti-
bacterial activity against the wound-associated pathogens, isolation of compounds from
these plants and other species has shown noteworthy activity and may be a new source of
antibacterial agents. Compounds isolated from the species discuss ed throughout the chap-
ter have been summarized below.
Aloe species
Anthraquinone compoun ds isolated from both A. ferox and A. excelsa exhibited antibac-
terial activity against wound-associated bacteria (Fig. 4.4). Three compounds, aloe-emodin,
166 4. Medicinal plants used in South Africa as antibacterial agents for wound healing
Medicinal Plants as Anti-infectives
chrysophanol, and aloin A, which showed antibacterial activity were isolated from the hex-
ane extract of the dried plant material. The MICs of aloe-emodin, chrysophanol,
and aloin A were 125, 250, and 62.5 μg/mL, respectively, against Bacillus subtilis.Against
Staphylococcus aureus the MICs were 125, .250, and 62.5 μg/mL, respectively, and MICs
of 250, 31.25, and 125 μg/mL were obtained against Staphylococcus epidermidis,respectively
(
Aaku, Dharani, Majinda, & Motswaiedi, 1998; Coopoosamy & Magwa, 2006; Kambizi et al.,
2008
). In addition, aloin A has been found to significantly accelerate wound healing in rats
and enhance the proliferation of human skin fibroblasts and endothelial cells in vitro.
The isolation and identification of these active compounds from A. barberae were con-
ducted using chromatographic and ultraviolet spectroscopic methods. The ethanolic and
dichloromethane leaf extracts were subjected to thin-layer chromatography (TLC) and
the UV spectra were obtained to identify possible compounds present. The results from
the TLC confirmed that phenolic compounds were present within the leaf extracts of
A. barberae which are hypothesized to be the antibacterial compounds, such as aloin deri-
vatives and chrysophanol, commonly found in aloe species. However, further isolation
and characterization of these phenolic compounds within A. barberae is needed to confirm
the exact chemical structure of these compounds (
Ndhlala et al., 2009a).
Elephantorrhiza elephantina
A study by Aaku et al. (1998) isolated dihydrokaempferol, kaempferol, (-)-catechin,
ethyl gallate, gallic acid, 2-(3,4-dihydroxyphenyl) ethanol, 4-hydroxybenzoic acid, ethyl-1-
O-β-
D-galactopyranoside, and quercetin-3-O-β-D-glucopyranoside from the 70% ethanolic
rhizome extract of E. elephantina (
Fig. 4.5). A TLC bioautography method was used to
determine the antibacterial activity of the isolated compounds against B. subtilis, S. aureus,
and P. aeruginosa. Each of the compounds was found to have antibacterial activity against
the tested pathogens only at a loading capacity of above 50 μg, except for gallic acid and
ethyl gallate which showed activity at loading capacities of 15 and 25 μg against B. subtilis
FIGURE 4.4 Major compounds isolated from Aloe species (A) aloin A, (B) aloe-emodin, and
(C) chrysophanol.
167Compounds present in plants traditionally used for wound healing in South Africa
Medicinal Plants as Anti-infectives
and 20 and 35 μg against S. aureus, respectively. However, the authors concluded that the
constituents may have a synergistic effect, as the 70% ethanolic rhizome extract and the
n-butanol semipure fraction showed higher activity than the compounds (
Table 4.1).
In a study by
Ming et al. (2017), kaempferol was found to inhibit 80% of S. aureus bio-
film formation at a concentration of 64 μg/mL, however, did not show antibacterial activ-
ity, which correlates with the study by
Aaku et al. (1998). This further corresponds to a
study by
Adamczak, O
˙
zarowski, and Karpi
´
nski (2020), where kaempferol showed an
MIC . 1000 μg/mL against both S. aureus and P. aeruginosa. However, in a study by
Tajuddeen, Sani Sallau, Muhammad Musa, James Habila, and Muhammad Yahaya (2014),
kaempferol was reported to have an MIC of 6.25 μg/mL against S. aureus, which was also
the MIC obtained for dihydrokaempferol. Against B. subtilis, dihydrokaempferol showed
an MIC of 1 mg/mL (
Zhou, Li, Wang, Liu, & Wu, 2007). Kaempferol has also been
reported to have wound-healing activity in both nondiabetic and diabetic wounds in rats
after a 14-day topical treatment of 1% (wt./wt.) kaempferol ointment (
O
¨
zay et al., 2019).
(-)-Catechin has been tested against three strains of S. aureus (BB568, EMRSA-15,
and EMRSA-16). The compound exhibited no activity against these strains with MICs
.256 mg/L. The compound was also tested in combination with the positive control oxa-
cillin and showed no potentiation of the antibiotic against the three strains (
Stapleton
et al., 2004
). Ethyl gallate showed activity against B. subtilis with an MIC of 1000 μg/mL.
Using a macrodilution and microdilution methods the compound was only active using
the macrodilution method with MICs of 6001200 and 6002400 μg/mL against P. aerugi-
nosa and S. aureus, respectively (
Mazurova et al., 2015). Vandal, Abou-Zaid, Ferroni, and
Leduc (2015)
reported an MIC of 1000 μg/mL against S. aureus and no activity against
P. aeruginosa ( . 1000 μg/mL).
Sato et al. (1997) reported the antibacterial activity of this
compound against S. epidermidis and P. aeruginosa with MICs of 1000 and 500 μg/mL,
respectively. In a study by
Mazurova et al. (2015) the MIC of gallic acid was determined
FIGURE 4.5 Compounds isolated from the 70% ethanolic rhizome extract of Elephantorrhiza elephantina
(A) dihydrokaempferol, (B) kaempferol, (C) (-)-catechin, (D) ethyl gallate, (E) gallic acid, (F) 2-(3,4-dihydroxy-
phenyl) ethanol, (G) 4-hydroxybenzoic acid, (H) ethyl-1-O-β-D-galactopyranoside, and (I) quercetin-3-O-β-D-
glucopyranoside.
168 4. Medicinal plants used in South Africa as antibacterial agents for wound healing
Medicinal Plants as Anti-infectives
using macrodilution and microdilution methods. The macrodilution MIC was determined
as 6001200 μg/mL and the microdilution MIC was 300600 μg/mL against P. aeruginosa.
The macrodilution MIC and microdilution MIC against S. aureus were 24004800 and
.4800 μg/mL, respectively.
Borges, Ferreira, Saavedra, and Simo
˜
es (2013) reported similar
MICs with 500 and 1750 μg/mL against P. aeruginosa and S. aureus, respectively. The com-
pound 4-hydroxybenzoic acid has been tested for its antibacterial activity against S. aureus
(ATCC 5838), S. epidermidis (12228), B. subtilis (ATCC 6633), and P. aeruginosa (KCTC 1628)
with an IC
50
of 926, 355, 956, and 619 μg/mL, respectively (Cho, Moon, Seong, & Park,
1998
). A recent study by Liu, Du, Beaman, Beth, and Monroe (2020) tested the compound
against S. epidermidis and it exhibited an IC
50
of 3.2 mg/mL after 4 h and 4 mg/mL after
24 h. The compound also exhibited antibacterial activity against drug-resistant S. epidermi-
dis with an IC
50
of 4 mg/mL after 4 h and 3.2 mg/mL after 24 h. When tested against S.
aureus the IC
50
was 5.2 mg/mL after 4 h and 4.5 mg/mL after 24 h. Against drug-resistant
S. aureus the IC
50
was 2.9 mg/mL after 4 h and 2.3 mg/mL after 24 h (Liu et al., 2020).
There is no reported antibacterial activity for the compounds 2-(3,4-dihydroxyphenyl) eth-
anol and ethyl-1-O-β-
D-galactopyranoside. Quercetin-3-O-β-D-glucopyranoside isolated
from Halostachys caspica was investigated for its antibacterial activity against S. aureus and
B. subtilis and exhibited MICs of 200 and 100 μg/mL, respectively. The compound also
exhibited an IC
50
of 167.61 and 56.00 μg/mL, respectively (Liu et al., 2010).
Erythrina lysistemon
In a study by Sadgrove, Oliveira, Khumalo, van Vuuren, and van Wyk (2020), seven iso-
flavone derivatives were isolated from the bark of E. lysistemon, namely, three pterocar-
pans (erybraedin A, phaseollidin, and cristacarpin), one flavonoid (abyssinone V-4
0
methyl
ether), one isoflavan (eryzerin C) and two isoflavonoids (alpumisoflavone and lysisteiso-
flavone), which were tested for antibacterial activity against various skin pathogens
(
Fig. 4.6). Erybraedin A was found to be the most active compound against the tested
FIGURE 4.6 Compounds isolated from the bark of Erythrina lysistemon (A) erybraedin A, (B) phaseollidin,
(C) cristacarpin, (D) abyssinone V-4
0
methyl ether, (E) eryzerin C, (F) alpumisoflavone, and (G) lysisteisoflavone.
169Compounds present in plants traditionally used for wound healing in South Africa
Medicinal Plants as Anti-infectives
pathogens with an MIC value of 2 μg/mL against both S. aureus and S. epidermidis, whereas
an MIC of 20 μg/mL was obtained against P. aeruginosa. Eryserin C was found to be the
second most active compound, with an MIC value of 5 μg/mL against both S. aureus and
P. aeruginosa, and an MIC value of 2 μg/mL against S. epidermidis. This was followed by
phaseollidin, which showed MIC values of 5, 10, and 20 μg/mL against S. epidermidis,
S. aureus, and P. aeruginosa respectively. Abyssinone V-4
0
methyl ether, alpumisoflavone,
cristacarpin, and lysisteisoflavone showed less activity against the tested skin pathogens
with MIC values of 59, 31, 156, and 62 μg/mL against S. aureus, MIC values of 117, 125,
412, and 26 μg/mL against S. epidermidis and MIC values of 260, 20, 78, and 31 μg/mL
against P. aeruginosa (
Sadgrove et al., 2020). In a study by Tanaka et al. (2002) cristacarpin
showed similar activity to that reported by
Sadgrove et al. (2020) with an MIC of
100 μg/mL against methicillin-resistant S. aureus.
Galenia africana
Ticha (2015) determined the antimicrobial activity of several flavanones and chalcones
isolated from G. africana (
Fig. 4.7). (E)-2
0
,4
0
-dihydroxylchalcone exhibited activity against
both S. aureus and methicillin-resistant S. aureus using the disk diffusion assay. The zone
of inhibition was 11 and 7 mm against S. aureus and MRSA, respectively, at a concentra-
tion of 0.5 mg/mL.
Melianthus comosus
AstudybyBedane et al. (2020) reported the isolation of six bufadienolides, 16β-formy-
loxymelianthugenin, 2β-acetoxymelianthusigenin, 2β-hydroxy-3β,5β-di-O-acetylhellebrigenin,
FIGURE 4.7 Flavanone and chalcone compounds isolated from Galenia africana, (A) (E)-2
0
,4
0
-dihydroxylchalcone,
(B) 7-hydroxyflavanone, (C) 2
0
,4
0
-dihydroxydihydrochalcone, (D) (S)-5,7-dihydroxy flavone, (E) 2
0
,5,7-trihydroxyflava-
none, (F) (S)-5,7-dihydroxy-2
0
-methoxy flavanone, (G) chromenone, (H) alpinetin, (I) (S)-2
0
-hydroxy-3,6
0
-dimethoxydi-
hydrochalcone, (J) (S)-4
0
,5-dihydroxy-7-methoxy flavanone, and (K) (S)-4
0
,5-dihydroxy-3
0
,7-dimethoxy flavanone.
170 4. Medicinal plants used in South Africa as antibacterial agents for wound healing
Medicinal Plants as Anti-infectives
2β-acetoxy-5β-O-acetylhellebrigenin, melianthusigenin, and 16β-hydroxybersaldegenin 1,3,5-
orthoacetate from a dichloromethane:methanol (1:1) extract prepared from the leaves of
M. comosus (
Fig. 4.8). While these compounds have not been tested for their antimicrobial
activity, several bufadienolide compounds have been tested against S. aureus, P. aeruginosa,
S. epidermidis, and B. subtilis. These compounds have also been isolated from the glandular
skin secretions of toad species and several species of Kalanchoe (
Cunha Filho et al.,
2005; Rodriguez, Iba
´
n
˜
ez, Rollins-Smith, Gutie
´
rrez, & Durant-Archibold, 2020; Stefanowicz-
Hajduk et al., 2020
).
Plectranthus fruticosus
Several diterpenoids including 10(14)-aromadendrene-4β,15-diol, ent-3β-acetoxy-labda-8
(17),12Z,14-trien-2α-ol, ent-12β-acetoxy-15β-hydroxykaur-16-en-19-oic acid, ent-12β-acetoxy-
7β-hydroxykaur-16-en-19-oic acid, ent-7β-hydroxykaur-15-en-19-oic acid, ent-12β-acetoxy-
17-oxokaur-15-en-19-oic acid, ent-7β-hydroxy-15β,16β-epoxykauran-19-oic acid, ent-labda-8
(17),12Z,14-triene-2α,3β-diol, methyl ent-12β-hydroxykaur-16-en-19-oate, methyl ent-12β-
acetoxy-7β-hydroxykaur-15-en-19-oate, ent-labda8(17),12Z,14-triene-2α,3β-dibenzoate, ent-12β-
acetoxy-15β-hydroxykaur-16-en-19-oate, and methyl ent-12β-acetoxy-17-oxokaur-15-en-19-oate
have been isolated from this species which have been tested against P. aeruginosa and
S. aureus. The diterpene kaurane was identified as the most active compound with an MIC of
62.5 μg/mL against S. aureus. None of the compounds exhibited antibacterial activity against
P. aeruginosa (
Gaspar-Marques, Fa
´
Tima Simo
˜
es, & Rodrı
´
guez, 2004)(Fig. 4.9).
Sutherlandia frutesce ns
There have been four cycloartane glycosides (sutherlandioside A, B, C, and D) isolated
from this species which have been tested for their antimicrobial activity against S. aureus,
FIGURE 4.8 Bufadienolides isolated from Melianthus comosus, (A) 16β-formyloxymelianthugenin, (B) 2β-acet-
oxymelianthusigenin, (C) β-hydroxy-3β,5β-di-O-acetylhellebrigenin, (D) β-acetoxy-5β-O-acetylhellebrigenin, (E)
melianthusigenin, and (F) 6β-hydroxybersaldegenin 1,3,5-orthoacetate.
171Compounds present in plants traditionally used for wound healing in South Africa
Medicinal Plants as Anti-infectives
methicillin-resistant S. aureus, P. aeruginosa; however, these showed no antimicrobial activ-
ity at the highest tested concentration of 20 μg/mL (
Fu et al., 2008)(Fig. 4.10).
Discussion
Africa is amongst one of the richest continents with regards to species richness and
plant biodiversity. It is estimated to have between 40,00045,000 higher plant species of
which approximately 10% are used medicinally for various diseases. This is largely due
to the tropical and subtropical climatic regions, allowing these species to flourish (
Agyare
et al., 2016
). Many southern African species have been identified through empirical evi-
dence and traditional knowledge as potential wound-healing agents, largely based on their
phytochemical composition. Various plant extracts and their secondary metabolites, which
FIGURE 4.10 Cycloartane glyco-
sides isolated from Sutherlandia fru-
tescens, namely, (A) sutherlandioside
A, (B) sutherlandioside B, (C)
sutherlandioside C, and (D) suther-
landioside D.
FIGURE 4.9 Kaurane, an active diterpenoid isolated from the ace-
tone extract of P. fruticosus.
172 4. Medicinal plants used in South Africa as antibacterial agents for wound healing
Medicinal Plants as Anti-infectives
have antibacterial activity, have been identified as potential leads for the development of
wound care products (
Chingwaru, Bagar, Maroyi, Kapewangolo, & Chingwaru, 2019).
Of the plant species evaluated in this chapte r, all the species were evaluated for their
antibacterial activity against at least one wound-associated pathogen; however, Aloe barber-
ae, Aloe excelsa, Elephantorrhiza elephantina, Erythrina lysistemon, Galenia africana, Grewia occi-
dentalis, Melianthus comosus, Plectranthus fruticosus, Polystichum pungens, and Sutherlandia
frutescens had no reports of in vitro or in vivo wound-healing activity.
South African Aloe species have shown potential for medicinal use in wound healing
and preventative action against microbial growth against certain strains of bacteria associ-
ated with wound infections (
Coopoosamy & Magwa, 2007; Ndhlala et al., 2009a; O’Brien
et al., 2011
). Research conducted on the antimicrobial activity of certain Aloe species has
shown a general trend in which Gram-positive bacteria are more susceptible in compari-
son to Gram-negative bacteria (
Pellizzoni, Ruzickova, Kalhotka, & Lucini, 1975). The
mechanism of antibacterial action of the compounds isolated from the various Aloe species
is hypothesized to be as a result of destabilization of the bacterial cell wall or oxidative
stress. However, further studies are required to determine the specific mode of action
for each compound. Although the anthraquinone compounds isolated from A. ferox and
A. excelsa displayed similar antibacterial activity, the activity of the crude leaf extracts of
A. barberae, A. excelsa, and A. ferox against Bacillus subtilis, Staphylococcus aureus, and
Staphylococcus epidermidis varied (
Coopoosamy & Magwa, 2007; Jia et al., 2008; Ndhlala
et al., 2009a
), which may be due to chemical and physiological differences amongst the
Aloe species as well as their growth conditions which may alter the accumulation of meta-
bolites within the plant tissue (
Malmir, Serrano, & Silva, 2017). However, limited research
has been conducted on the differences in chemical composition of anthraquinone com-
pounds isolated from the above-mentioned Aloe species. Toxicity studies conducted using
A. ferox have shown that leaf extracts prepared from A. ferox have shown no adverse der-
matological effects and no in vitro or in vivo toxicity (
Andersen, 2007). There are currently
no toxicity studies that have been conducted using A. excelsa; however, A. barberae has
been reported to be nonmutagenic.
Despite reports showing that anthraquinone compounds, isolated from the Aloe species,
displayed promising antibacterial activity, there is limited research conducted on the activ-
ity and use of these compounds against Pseudomonas aeruginosa. Whilst the anthraquinone
compounds isolated from the Aloe species have been tested for their antibacterial activity,
there are no reports on the in vitro or in vivo wound-healing activity of aloe-emodin and
chrysophanol. These compounds have been identified as the major constituents in Aloe
species, however, other compounds could potentially be responsible for the activity, there-
fore, additional compound isolation and elucidation shou ld be considered. Furthermore,
confirmation of whether these are also major constituents present in A. barberae should be
evaluated.
Compounds have been isolated from most of the species described in this work, with
the exception of Grewia occidentalis. The compound kaempferitrin isolated from the aerial
parts of Urtica urens has not been reported for its antibacterial or wound-healing activity
and should be considered for further evaluation. Similarly, compounds isolated from
M. comosus have not been evaluated for their antibacterial or wound-healing activity, even
though various extract preparations of M. comosus have shown promising antibacterial
173Discussion
Medicinal Plants as Anti-infectives