Calorilvietric Investigation of the Action of Propolis on Bacterial Growth and Metabolism
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Date
1996-06
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Addis Ababa University
Abstract
Power-time (P-t) curves were established by growing Micrococcus /uteus in a flow
calorimetric system using different inoculum densities to see if inoculum size affects
calorimetric experiments. The P-t curves obtained for the lower inoculum densities used were
the same in several aspects except length of the calorimetric lag phase. Spectrophotometric
and polarographic experiments were done simultaneously with the calorimetric experiments
to see if results from the latter are true pictures of metabolic events in the fermenter or
experimental artifacts introduced due to separation of fermenter from the calorimeter. Results
from experiments with the different methods showed the same pattern indicating that
separation of fermenter from the calorimeter does not introduce error at the pumping rate used
(100 mL 11• 1). Extraction of propolis was done with 70% methanol as a solvent. The yield of
extraction was 21 % (w/w) for all propolis samples used. Addition of water to the ethanol
solution of extract of propolis (EEP) resulted in precipitation of the water insoluble
components and hence separation of the water soluble from the water insoluble components.
The proportion of water soluble components was very low in propolis sample 3 (prop3).
Calorimetric experiments with propolis were done by incorporating increasing
concentrations of tincture at different phases of the P-t cun•e and different propolis samples
at the mid exponential phase of the P-t curve for comparison of their effect. It was found that
effect of propolis can be detected at all phases of growth. However, comparison of
antibacterial activities for the different concentrations of propolis used was not possible at the
lag phase. Variation in activity was observed among the different propolis samples in their effect
on the drop of the P-t curve which is directly proportional to the amount of cells killed or
inactivated, and the time needed for the resumption of growth after the curve has fallen off
to a minimum value. Though incorporation of tincture resulted in a drop of the P-t curve
comparable to other propolis samples, growth was resumed sooner suggesting lower
inhibitory effect on the survivors. But propolis sample 2 (prop2) possesses higher killing and
inhibitory effect on the survivors.
For all propolis samples used the strength of antibacterial activity, based on drop of
the P-t curve and subsequent effect. could be ordered as follows: EEP > water insoluble
component > water soluble component. For some propolis samples the effect of EEP was
greater than even the sum of two of its components at a ce11ain concentration. It was therefore
deduced that the water soluble and insoluble components exhibit synergistic interactions in
EEP.
The calorimetric method was found out to be slightly less sensitive to detect effect of
lower concentrations of propolis than the agar well diffusion assay method. However, the
fom1er method had a very short assay time and clearly demonstrated that the mechanism of
action of propolis is bactericidic.
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Biology