Buwa-Komereng, L.V.Dubeni, Zimasa Busisiwe2026-08-072026-08-072024http://hdl.handle.net/20.500.11837/4292PhD thesisPoultry meat consumption has increased drastically over the last two decades in many countries. Among muscle foods, poultry and its products are more susceptible to microbial spoilage because of the diversity in nutrient composition. The cell-to-cell communication or quorum sensing (QS) leads to biofilm formation and causing other virulence factors which are extreme problems for food safety, biofilm related infectious diseases etc. Quorum sensing (QS) controls several functions between bacterial colonies and is regulated via signaling molecules called “autoinducers”. As the pathogens evolve and acquire resistance to a higher concentration of the drugs, the dosage of the drug may be increased to suppress the infection which on the other hand may cause undesirable side effects in the host. With the difficulty in treating recalcitrant infections and the growing resistance to antibiotics, new therapeutic modalities are becoming increasingly necessary. The interruption of bacterial quorum sensing (QS), or cell-cell communication is known to attenuate virulence, while limiting selective pressure toward resistance. Chemical preservatives used to increase the shelf-life of food are reported to have health issues associated with them. The misuse of antibiotics to treat infectious diseases in healthcare, animal husbandry, and agriculture has resulted in a vast increase in antibiotic resistance, hence the growing need for antibacterial compounds. With the difficulty in treating recalcitrant infections and the growing resistance to antibiotics, new therapeutic modalities are becoming increasingly necessary. Subsequently, interest in the application of naturally occurring preservatives in muscle foods has amplified. One possible source for the isolation of antibiotics is (medicinal) plants. Natural products are still a potential source of drug leads since they contain a wide array of structurally diverse compounds. This study was, therefore, aimed at evaluating the phytochemicals, antibacterial, antioxidant, anti-biofilm, anti quorum sensing activity and cytotoxicity potential of Moringa oleifera leaf extracts. Various phytochemicals were also characterized using nuclear magnetic resonance (NMR) and ultra-performance liquid chromatography-mass spectrometry (UPLC-MS respectively. This work evaluated qualitatively and qualitatively the phytochemicals present in Moringa oleifera leaf extracts (methanol, acetone, ethanol, aqueous) using various methods. The different concentrations (1, 0.75, 0.50, 0.25 mg/ml) of M. oleifera leaf extracts were evaluated for their antioxidants activity and various phytochemicals were also characterized using the 2,2-Diphenyl-1-picrylhydrazyl (DPPH) Radical Scavenging, Ferric Reducing/Antioxidant Power (FRAP), 2,2′-azino-bis(3-ethylbenzothiazoline6-sulfonic acid (ABTS) Free Radical Scavenging methods and Nuclear magnetic resonance (NMR) and Ultra-performance liquid chromatography-mass spectrometry(UPLC-MS), respectively. The gar, broth dilution method, and plate count method were used to determine the minimum inhibitory concentration (MIC), minimum bactericidal (MBC) and time kill kinetics of M. oleifera leaf extracts against bacterial strains (Vibrio cholerae, Klebsiella pneumoniae ATCC 4352, Pseudomonas aeruginosa ATTC 19, E. coli ATCC 8739 and S. aureus), respectively. While the antibiofilm and antiquorum inhibitory activity of the M. oleifera leaf extracts using two Salmonella enteritidis and the biomonitoring strain, Chromobacterium violaceum. The cytotoxicity potential of various concentrations of M. oleifera leaf extracts was also evaluated using Vero cells. The potential application of 1, 0.75, 0.50, 0.25% methanolic extract of M. oleifera extracts as natural preservatives of chicken meat was also evaluated using standardized methods (ISO methods) for the detection and enumeration of microorganisms studied. This was done by evaluating the survival and growth of Salmonella, Listeria monocytogenes, Escherichia coli, and aerobic count (APC) in raw ground chicken meat stored under 4 degrees Celsius and 25 degrees Celsius for four days. Our findings revealed the presence of phenols, flavonoids, alkaloids, terpenoids, tannins, and steroids in all extracts investigated. The total phenolic content ranged from 34.1 to 68.67 mg/g of the dry weight of extract expressed as gallic acid equivalents. The MIC value of the methanol and acetone extracts was the same for all the test organisms in the pool, 6.25mg/ml and 100 mg/ml respectively, whereas ethanol and water extracts displayed no antagonistic activity. The methanolic extract was found to be bactericidal with complete elimination of most of the test organisms within 2 hours of incubation. Average log reductions for the extract ranged between 0.7782 - 1.4771 log10 CFU at a 1X MIC concentration. A correlation was observed between the killing curves and the MIC of the leaf extract against the test organisms. The anti-biofilm activity results of the various M. oleifera leaf extracts tested, varied, with the water extracts having a good ABF activity (> 50% Inhibition) compared to the positive controls through the 24 hours. The Hexane extracts showed good activity at the end of the experiment whereas dichloromethane showed good activity on the T0 of the experiment. Other test extracts on the other hand (Methanol, Ethanol, and Acetone) showed no anti-biofilm activity ABF activity (0 % or less) against S. enteritidis throughout the experiment (T0-T24). With regards to the ant quorum sensing activity, the test text extracts exhibited varying levels of pigment inhibition at the tested concentrations and the quantitative estimation of violacein inhibition in the presence of test M. oleifera leaf extracts was also performed). The minimum inhibitory concentration (MIC) of the test extracts followed this trend; methanol, ethanol, dichloromethane, acetone, hexane, and aqueous ranging between (0.16-1.25 mg/ml). The minimum quorum-sensing inhibitory concentration (MQSIC), the lowest concentration indicated by bacterial growth and lack of violacein pigmentation followed this trend methanol, dichloromethane, hexane, ethanol, acetone, and aqueous, ranging between (0.04-0.16 mg/ml). The results regarding the antibacterial effects of the plant extracts on meat showed significant reductions. All treatments were efficient (P < 0.05) in suppressing and slowing the growth of test bacteria in meat at all temperatures (4 degrees Celsius and 25 degrees Celsius) tested. The concentration of 0.50% treatment showed the strongest (P < 0.05) antibacterial effect by eliminating E. coli in raw chicken breast meat during storage at 25 degrees Celsius of the storage period as compared to other treatments. Of all the treatments tested, 0.25% MOME treatment also showed the strongest antimicrobial effects against Listeria monocytogenes, in raw meat during storage at 4 degrees Celsius resulting in complete elimination whereas other treatments showed regrowth on the last day of incubation. This study demonstrates that M. oleifera could be a good natural antimicrobial treatment to suppress natural bacterial flora and foodborne pathogens in raw chicken meat. This study further demonstrates the potential of M. oleifera leaf as a promising source for the isolation of new antibiotic compounds.enMoringa oleiferaAntibacterial agentsQuorum sensing (Microbiology)Thesis