Antibacterial Efficacy of Mangrove Rhizophora mucronata Extracts on Aquatic Bacterial Pathogens
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Date
2013
Journal Title
Journal ISSN
Volume Title
Publisher
Uva Wellassa University of Sri Lanka
Abstract
Medicinal plants contain components of therapeutic value and are used as remedies for
human/animal diseases. They are environmentally friendly due to less toxicity and have
minimal health hazards (Opara and Wokocha, 2008). Mangrove plant extracts and its major
chemical classes displayed various levels of antibacterial, antifungal, antifouling, antiviral and
free radical scavenging effects due to their bioactive compounds (Bandaranayake, 2002).
Bacterial infections cause severe economic losses to the aquaculture industry which increased
the use of antimicrobial agents significantly as a treatment (Alderman and Michel, 1992).
Improper usage and presence of drug residues lead to the development of resistant strains of
pathogenic bacteria. Therefore, novel antibacterial compounds of natural products which
degrade easily need to be synthesized to overcome above consequences. Aim of this study was
to find out the antibacterial efficacy of Mangrove Rhizophora mucronata extracts on aquatic
bacterial pathogens, to be used as a remedy to treat fish diseases.
Methodology
Fresh matured leaves of six mangrove plant species (Avicennia marina, Lumnitzera racemosa,
Bruguiera sexangula, Acanthus ilicifolius, Excoecaria agallocha and Rhizophora mucronata)
were collected from mangrove reserve at Kadolkele, Negombo and were brought to the
laboratory for making extractions. Initially, preliminary trials were conducted for identification
of
most
suitable
species
with
antibacterial
properties
against
four
aquatic
pathogens
Listeria
monocytogenes) in vitro by well diffusion method. Upon identification of Rhizophora
mucronata having the highest inhibitory zone for tested bacteria, further analysis were
performed using various parts such as roots, barks, flowers and fruits of R. mucronata. The
solvent was extracted by mixing 8 g of each part of mangrove in powder form, with 125 ml of
95% methanol and evaporating methanol using rotary flash evaporator (model 519-00000-00-
3). Antibacterial efficacy was assessed against all four species of fish pathogens, using
was used as the
positive control against Rhizophora mucronata extractions of 350 mgml each. After 24 hour
incubation at 25
o
C, the diameters of the inhibitory zones were obtained and statistically
analyzed by using One way-ANOVA incorporated in Minitab version 16.
Results and Discussion
All six mangrove species showed antibacterial activity against Listeria monocytogenes,
Pseudomonas fluorescens, and Pseudomonas aeruginosa significantly (p<0.05) but insignificant
for Shigella flexneri (p>0.05). Highest inhibition zones were observed in Rhizophora
mucronata leaf extract against all bacteria examined for the study (Table 1). Rhizophora
mucronata extracts (root, bark, fruit and flower) also exhibited positive inhibition zones for all
the tested bacterial species cultured in vitro.
Root and bark extracts possessed higher antibacterial potential when compared to the fruit and
flower extracts. Rhizophora leaf extracts showed highest inhibition for Listeria monocytogenes
and Pseudomonas fluorescens while root and bark extracts were effective against Shigella
flexneri and Pseudomonas aeruginosa respectively (Figure 1). The overall mean comparative
evaluation on antibacterial efficacy of Rhizophora mucronata extracts displayed the highest in
leaves followed by the root, bark and fruit extracts. The minimum antibacterial activity was
observed in the flower extracts.
Description
Keywords
Aquaculture and Fisheries, Aquatic Plant, Aquatic Resources, Antibacterial, fish Industry, Environmental Science, Medicinal plants