By Agbo, Ifeoma Chinyere
Studies on antibacterial activities and in vitro interactions of methanolic stem bark
extracts of S. micranthus and P. guajava against 35 multi-resistant Gram negative bacteria
was carried out. The plant materials were extracted and the phytochemical analyses of the
plant extracts were performed by standard procedures. The extracts were tested for
antibacterial activity using agar well diffusion method. The minimum inhibition
concentrations (MICs) of the plant extracts and antibiotic used against the test multi-resistant
bacteria were also determined by agar dilution technique. The interactions between the plant
extract and some standard antibiotic against the test bacteria were also evaluated by
checkerboard combination method. The Fractional Inhibitory Concentration (FIC) of the
extracts and antibiotics were determined and the effect of the interaction assessed by
calculating the Fractional Inhibition Concentration Index (FICI). The effects of ethylene
diamine tetra acetic acid (EDTA) and reserpine on the resistance of the test bacteria was
evaluated by disc diffusion method. The mean IZD produced by each antimicrobial agent in
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the presence and absence of EDTA and reserpine were compared using One-way Analysis of
Variance (ANOVA) at 5% probability level.
Phytochemical studies revealed that P. gu4ava contains carbohydrates, glycosides,
tannins and proteins as its major constituents while S. micranthus contains carbohydrates,
proteins and terpenoids as its major constituents. The results of the study showed that the
plant extracts have antibacterial activity against the multi-resistant Gram negative organisms.
Out of the 35 multi-resistant strains tested, 33 were sensitive to S. micranthus with inhibition
zone diameter (IZD) ranging from 10 to 14mm while 25 of the strains tested were sensitive to
P. guajava with IZD ranging from 10 to 20mm. The MIC of S. micranthus ranged fiom 2.5 to
lOmg/rnl while that of P. guajava ranged from 2.5 to 80mg/ml. The interaction between S.
micranthus and ampicillin showed synergism against E. coli (Eco 15) and Salmonella strains
and additive effect against Proteus species while combination of S. micranthw. and
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tetracycline resulted in synergistic and additive effects against E. coli, Proteus spp and
Salmonella gallimmm strains except SG4 which showed both indifferent and antagonistic
effects. The combination of P. guajava and ampicillin showed synergism against E. coli and
additive effect against Proteus. Synergism also resulted in the combination of P. guajava and
tetracycline against E. coli and additive effect against S. gallinarum. Synergistic effects were
also obtained in the combination of ampicillin and gentamicin against Salmonella and
Proteus species. The combination of P. guajava and S. micranthus resulted in synergistic
effect against E coli and Salmonella strains. In the presence of EDTA and reserpine there was
significant (P