In vitro antioxidant and antibacterial activity of Crude extracts of some freshwater cyanobacteria
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Date
2023
Journal Title
Journal ISSN
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Publisher
University of Zululand
Abstract
Commonly available antibiotics are increasingly becoming ineffective due to the
astronomic rise of antimicrobial resistance (AMR). As a result, there is a need for the
discovery of new antibiotics and antioxidants from natural products.
Cyanobacteria possess a myriad of significant secondary metabolites among which
potential antibacterial and antioxidant could be found. The aim of this study was to
exploit the potential metabolite reservoir of cyanobacteria towards the development of
novel antimicrobial compounds. Freshwater cyanobacteria, Cylindrospermum
alatosporum NR125682.1 and Loriellopsis cavenicola NR117881.1, utilized in this
study were isolated from Vulindlela area, KwaZulu-Natal, SA. They were propagated
on BG-11 media, identified, and characterized through 16S rRNA sequencing. The
cyanobacteria were sequentially extracted with hexane, dichloromethane (DCM) and
ethanol. The extracts were screened for their antioxidant capacity using DPPH, ABTS,
OH* radicals and metal chelating potential. The in silico molecular docking of the major
constituents of the extracts against β-lactamase was also evaluated.
The in vitro antibacterial potential of the extracts was evaluated using the broth microdilution
method against some selected gram-positive and gram-negative clinical
bacterial isolates. The effect of the extracts on the bacterial membranes was evaluated
using the lactate dehydrogenase assay. The efflux pump inhibitory potential was
investigated by measuring the percentage cytoplasmic accumulation of rhodamine.
Beta-lactamase inhibitory potential was investigated along with synergistic potential
when combined with erythromycin. The ability of the extracts to effect DNA damage
was also evaluated.
The crude extracts were moderate antioxidants, scavenging free radicals with IC50
range of 6-10 μg/ml and metal chelating efficiency IC50 values ranging from 44-72
μg/ml. Despite the encouraging (-6.6, -6.3 kJmol-1) binding affinity of some of the
phytochemicals in the extracts following molecular docking against beta-lactamase,
the in vitro inhibition of beta-lactamase indicates that all six extracts were poor
inhibitors of the enzyme with a high IC50 value of 5.6 mg/ml.
The ethanol crude extract of both isolates was the most efficient with a minimum MIC
value of 0.7 mg/ml against the tested resistant bacteria. The ethanol extract of
Loriellopsis cavenicola NR117881.1 effectively inhibited efflux pump activity, with up
to 60% rhodamine accumulation in the bacteria tested. The extracts effected cell
membrane damage on the tested bacteria. The extract also exhibited synergism when
combined with erythromycin against some of the tested bacteria. Only the DCM extract
of Loriellopsis cavenicola NR117881.1 effected DNA damage.
The various bioactivity exhibited by the extracts suggest potential for the development
of antibacterial and antioxidant active agents with multiple beneficial effects.
Description
A Thesis submitted to the Faculty of Science, Agriculture and Engineering in fulfilment of the requirements for the Degree of Master of Science in the Department of Biochemistry and Microbiology at the University of Zululand, South Africa [2023].