Table 3. Minimal Inhibition Concentration (MIC) of aqueous and ethanolic extracts from selected plants against
Staphylococcus aureus and Pseudomonas aeruginosa bacterial strains.
Minimum Inhibition
Concentration (mg/mL)
Plant
Bacteria
Extract
specie
specie
type
30
3
0.3
Datura Stramonium
Staphylococcus
Aqueous
+
−
−
Pseudomonas
Aqueous
+
−
−
Galinsoga Parviflora
Staphylococcus
Aqueous
−
−
−
Pseudomonas
Aqueous
−
−
−
Racinus Communis
Staphylococcus
Aqueous
+
+
−
Pseudomonas
Aqueous
+
+
−
Datura Stramonium
Staphylococcus
Ethanolic
+
−
−
Pseudomonas
Ethanolic
+
−
−
Galinsoga Parviflora
Staphylococcus
Ethanolic
+
−
−
Pseudomonas
Ethanolic
+
−
−
Racinus Communis
Staphylococcus
Ethanolic
+
−
−
Pseudomonas
Ethanolic
+
−
−
‘−’ No bacterial activity, ‘+’ Bacterial activity present
5 DISCUSSIONS
5.1 Antibacterial efficacy of aqueous and ethanolic
plant extracts
With the increasing search for suitable antimicrobial
agents that can replace the existing synthetic ones, natural resources like plants have been the major focus
since they have been proven to have phytochemical
properties that are capable of controlling the growth of
microorganisms without having any toxic effects and
they are eco-friendly (Akanmu, Bulama, Balogun, &
Musa 2019; Fg et al. 2016; Mansour, Saif, & Al-fakih
2017). In the present study, the antibacterial activity of different plant extracts was evaluated against
Gram-positive and Gram-negative bacterial strains. It
was indicated (Table 1) that all extracts inhibited bacterial growth, although with variation. This may be
attributed to the varying phytochemicals that could
have been contained within the extracts that are capable of imparting antibacterial activities via various
mechanisms. The findings done by Mansour et al.
(2017) on phytochemical screening of plant extracts
revealed that there are mainly five phytochemicals
(flavonoids, tannins, alkaloids, glycosides, and terpenoids) that are found naturally in most plants and
are well-known for their biological activities, which
include bactericidal, fungicidal action among others,
thus conferring the antibacterial activity of the analysed aqueous and ethanolic plant extracts. Also, more
studies have confirmed that in addition to the five
main phytochemicals responsible for bacterial activity against different bacterial strains, there are others
like phenols, lignins, saponins, and sterols that are
mainly found in plant leaves (Ali et al. 2017; Sayyed
& Shah 2014). All these compounds have been found
to have also pharmacological properties like antidiabetic activity, anti-inflammatory activity, antimicrobial activity, among others (Marwat, Khan, & Baloch
2017).
The current study further revealed that aqueous
extracts of all plants gave improved resistance, thus
a bigger zone of inhibition, ranging from 8–18 mm
against both Staphylococcus aureus and Pseudomonas
aeruginosa bacterial strains, compared to ethanolic
extracts with 6–13 mm. This result differs from what
is well-known from various studies (Udochukwu et al.
2015; Yu et al. 2014) where organic extracts showed a
greater or same activity than aqueous extracts. This
could be attributed to the chemical composition of
plants and variations in the ability of the solvent
to dissolve the grounded plant leaves, thus influencing the phytochemicals extracted. In related findings,
Oluwajobi et al. (2019) evaluated the antibacterial
and antifungal activities of aqueous and methanol leaf
extracts from Psidium guajava, Vernonia amygdalina,
and Azadiracta indica against different microbial isolates. The obtained range of zone of inhibition for
aqueous extracts against both bacteria and fungi was
greater than for methanol extracts. This was so due
to the presence of all the analysed phytochemicals
including tannins which were found in large quantities as opposed to methanol extracts where glycoside
and anthraquinone were found to be missing. Furthermore, Kadi et al. (2011) used the disc diffusion
test to evaluate the antibacterial activity of ethanolic
and aqueous extracts from Punica granatum L. bark
against different bacterial strains. The results showed
aqueous macerate extracts to have higher antibacterial activity than ethanolic macerate extracts. This is
agreement with the findings of Atef et al. (2019) where
water extracts of M. oleifera and M. recutita plants
demonstrated better activity against the selected sensitive isolates compared to ethanol extracts from both
plants.
The study also demonstrated that there was
higher activity against Staphylococcus aureus (Grampositive) bacteria for all plant extracts (aqueous and
ethanolic) compared to Pseudomonas aeruginosa
99
Staphylococcus aureus and Pseudomonas aeruginosa bacterial strains.
Minimum Inhibition
Concentration (mg/mL)
Plant
Bacteria
Extract
specie
specie
type
30
3
0.3
Datura Stramonium
Staphylococcus
Aqueous
+
−
−
Pseudomonas
Aqueous
+
−
−
Galinsoga Parviflora
Staphylococcus
Aqueous
−
−
−
Pseudomonas
Aqueous
−
−
−
Racinus Communis
Staphylococcus
Aqueous
+
+
−
Pseudomonas
Aqueous
+
+
−
Datura Stramonium
Staphylococcus
Ethanolic
+
−
−
Pseudomonas
Ethanolic
+
−
−
Galinsoga Parviflora
Staphylococcus
Ethanolic
+
−
−
Pseudomonas
Ethanolic
+
−
−
Racinus Communis
Staphylococcus
Ethanolic
+
−
−
Pseudomonas
Ethanolic
+
−
−
‘−’ No bacterial activity, ‘+’ Bacterial activity present
5 DISCUSSIONS
5.1 Antibacterial efficacy of aqueous and ethanolic
plant extracts
With the increasing search for suitable antimicrobial
agents that can replace the existing synthetic ones, natural resources like plants have been the major focus
since they have been proven to have phytochemical
properties that are capable of controlling the growth of
microorganisms without having any toxic effects and
they are eco-friendly (Akanmu, Bulama, Balogun, &
Musa 2019; Fg et al. 2016; Mansour, Saif, & Al-fakih
2017). In the present study, the antibacterial activity of different plant extracts was evaluated against
Gram-positive and Gram-negative bacterial strains. It
was indicated (Table 1) that all extracts inhibited bacterial growth, although with variation. This may be
attributed to the varying phytochemicals that could
have been contained within the extracts that are capable of imparting antibacterial activities via various
mechanisms. The findings done by Mansour et al.
(2017) on phytochemical screening of plant extracts
revealed that there are mainly five phytochemicals
(flavonoids, tannins, alkaloids, glycosides, and terpenoids) that are found naturally in most plants and
are well-known for their biological activities, which
include bactericidal, fungicidal action among others,
thus conferring the antibacterial activity of the analysed aqueous and ethanolic plant extracts. Also, more
studies have confirmed that in addition to the five
main phytochemicals responsible for bacterial activity against different bacterial strains, there are others
like phenols, lignins, saponins, and sterols that are
mainly found in plant leaves (Ali et al. 2017; Sayyed
& Shah 2014). All these compounds have been found
to have also pharmacological properties like antidiabetic activity, anti-inflammatory activity, antimicrobial activity, among others (Marwat, Khan, & Baloch
2017).
The current study further revealed that aqueous
extracts of all plants gave improved resistance, thus
a bigger zone of inhibition, ranging from 8–18 mm
against both Staphylococcus aureus and Pseudomonas
aeruginosa bacterial strains, compared to ethanolic
extracts with 6–13 mm. This result differs from what
is well-known from various studies (Udochukwu et al.
2015; Yu et al. 2014) where organic extracts showed a
greater or same activity than aqueous extracts. This
could be attributed to the chemical composition of
plants and variations in the ability of the solvent
to dissolve the grounded plant leaves, thus influencing the phytochemicals extracted. In related findings,
Oluwajobi et al. (2019) evaluated the antibacterial
and antifungal activities of aqueous and methanol leaf
extracts from Psidium guajava, Vernonia amygdalina,
and Azadiracta indica against different microbial isolates. The obtained range of zone of inhibition for
aqueous extracts against both bacteria and fungi was
greater than for methanol extracts. This was so due
to the presence of all the analysed phytochemicals
including tannins which were found in large quantities as opposed to methanol extracts where glycoside
and anthraquinone were found to be missing. Furthermore, Kadi et al. (2011) used the disc diffusion
test to evaluate the antibacterial activity of ethanolic
and aqueous extracts from Punica granatum L. bark
against different bacterial strains. The results showed
aqueous macerate extracts to have higher antibacterial activity than ethanolic macerate extracts. This is
agreement with the findings of Atef et al. (2019) where
water extracts of M. oleifera and M. recutita plants
demonstrated better activity against the selected sensitive isolates compared to ethanol extracts from both
plants.
The study also demonstrated that there was
higher activity against Staphylococcus aureus (Grampositive) bacteria for all plant extracts (aqueous and
ethanolic) compared to Pseudomonas aeruginosa
99