antibacterial effect of C. macrostachyus stem bark was tested using the
agar well diffusion and broth dilution methods.
Each of the extracts tested in the present study displayed antibacterial
activity on all bacterial strains tested. Though, 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 study, chloroform, methanol, and water extracts of C. macrostachyus
stem bark were evaluated for their antibacterial activity against Gram-negative
(E. coli) and Gram-positive (S. aureus) bacteria, which are the major
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 medicinal plant.
this study, C. macrostachyus stem
bark extracted by methanol has shown the highest inhibition zone (17+1)
against S. aureus (standard)
and the lowest zone of inhibition was recorded in E. coli (clinical). It
is reported that Gram-positive bacteria are more susceptible to antibiotics since
they have only an outer peptidoglycan layer which, is an ineffective barrier (Lulekal
et al., 2014; Karou et
al., 2005). But 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
al., 2005). In addition to this periplasmic space of
Gram-negative bacteria contains enzymes, which are able to break strange
molecules and become to be less susceptible to plant extracts than the Gram-positive
ones. Several research findings supported this justification,
therefore extracts from some medicinal plants were found to be more effective
against Gram-positive bacteria than 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 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
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 was 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.