antibacterial analysis was performed using the agar well diffusion and broth dilution techniques. Each of the
extracts tested in the present study displayed antibacterial activity on all
the bacterial strains tested. However, differences were observed between antibacterial
activities of the extracts. These differences could be due to the variations in
the chemical composition of these extracts.
the present investigation, chloroform, methanol, and water extracts of C. macrostachyus
stem bark were evaluated for examination of their antibacterial activity
against Gram-negative (E. coli) and
Gram-positive (S. aureus) bacteria,
which was regarded as important human pathogenic microorganisms. Antibacterial
activity of each plant extract was tested by agar well diffusion and broth dilution (MIC) methods. The
extracts from C. macrostachyus stem
bark persuaded growth inhibition against all the studied bacterial pathogens.
Our results illustrated that between the bacterial strains there was variation
in susceptibility to extracts. This may be due to the antibacterial effect of
the extract depends on the bacterial strain and the extraction solvent used to
extract the phytochemicals which contain antibacterial effect from the
this study, C. macrostachyus stem
bark extracted by methanol has shown the highest inhibition zone (17+1)
against S. aureus (standard)
and the lowest inhibition zone was seen in E. coli (clinical). It is
reported that Gram-positive bacteria should be more susceptible since they have
only an outer peptidoglycan layer which is an ineffective barrier (Lulekal et al., 2014; Karou et al., 2005). Gram-negative bacteria have
an outer phospholipidic membrane that makes the cell wall impermeable to
lipophilic solutes, whereas the porines contain a selective barrier to
hydrophilic solutes with an elimination limit of about 600 Da (Karou et
al., 2005). The
periplasmic space of Gram-negative bacteria also contains enzymes, which are able
to break strange molecules and become to be less susceptible to plant extracts
than the gram positive one. Numerous results
confirmed this explanation, thus some plant extracts were found to be more
active against Gram-positive bacteria than against Gram-negatives (Kelmanson et al., 2000; Masika and Afolayane, 2002).
The lowest inhibition zone was recorded against E. coli which is the clinical isolate; this may be due to
development of resistance in the clinical isolated.
extract of the C. macrostachyus stem
bark was the second strong extract for its antibacterial activity and this is
in agreement with Taye et al. (2011).
But C. macrostachyus water extract
had lower activity against the all bacteria tested. This indicates, in
comparison to water, the active ingredient which inhibits the growth of
bacteria may dissolve better in methanol. However, Sendeku et al. (2015) reported chloroform extract from C. macrostachyus leaves shows significant antimicrobial activity.
Furthermore, water extract from leaves of P. acerifolium had been reported
to have strong antimicrobial activity against several gram positive and gram
negative human pathogenic bacteria (Thatoi et
al., 2008) and as stated by Dabur et al., 2007, the water extracts of A.
nilotica, J. zeylanica, L. camera and S. asoca, were found to
be the most active against different bacteria as well as fungal pathogens. It
is clear that the effectiveness of the extracts largely depends on the type of
solvent used to extract the phenolic compound from plants. The organic extracts
provided more powerful antimicrobial activity as compared to the water
extracts. This observation clearly indicates that the existence of non-polar
residues in the extracts which have higher both bactericidal and bacteriostatic
abilities. Thatoi et al., 2008,
mentioned that most of the antibiotic compounds already identified in plants
are reportedly aromatic or saturated organic molecules which can easily
solubilized in organic solvents. Similar results showing that the alcoholic
extract having the best antimicrobial activity is also reported by Antarasen and AmlaBatra (2012) in
Melia azedarach leaf extracts
antimicrobial analysis using the MIC value is been used by many researchers.
In the present study the MIC value of the active C. macrostachyus stem bark extracts obtained were lower than the
MBC values suggesting that the extracts were bacteriostatic at lower concentration
but bactericidal at higher (Maji et al., 2010; Antarasen and Amlabatra,
2012). Minimum inhibitory concentration values of 62.5–500 mg/ml. However Jackie
et al. (2016) reported MIC value range
from 125-500mg/m of C. macrostachyus
ethanol extract against selected human pathogens.When testing methanol extracts
of C. macrostachyus leaves and roots
Wagate and colleagues found MICs from 15.6
to 250 mg/ml against three bacteria, E.
coli, Bacillus cereus, and Pseudomonas aeruginosa.
our investigation, it is concluded that the active antibacterial present in the
stem bark of C. macrostachyus were methanol
and chloroform-soluble. The active ingredients contained in extract of
chloroform are quite effective against standard strains of S. aureus and E. coli
along with activity against the remaining whereas the activity in methanol extract
showed efficacious results against all the tested organisms.Further studies
should be conducted with different extraction solvents and toxicity and
phytochemical analysis must be performed on these plants to use as sources and
templates for the synthesis of drugs to control disease-causing bacteria.
authors of this paper are thankful to the office of the vice president for research
and community service, University of Gondar for their modest financial
authors have not declared any conflict of interests.